# data[].attributes.attachment_link.description
By closing this popup and using MolView, you agree to the Terms of Use.

# data[].attributes.body
REFLECTION: https://docs.google.com/document/d/1w4zfyt7aMI4VuD4cxJx7FdSQv_HPlfS47oj8uoCxq0A/edit

UPDATED (ESSENTIAL):
https://docs.google.com/document/d/19R_j4r8bYmLGdnWClorVIdc_dgOqLEotJ97gjO9RZvs/edit#heading=h.c1dvu3p7ulgy

# data[].attributes.attachment_link.description
Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

# data[].attributes.attachment_link.description
Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

# data[].attributes.attachment_link.description
Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

# data[].attributes.attachment_link.title
Google Forms - create and analyze surveys, for free.

# data[].attributes.attachment_link.description
Create a new survey on your own or with others at the same time. Choose from a variety of survey types and analyze results in Google Forms. Free from Google.

# data[].attributes.attachment_link.readable_text
One of the biggest challenges facing students taking IB chemistry is coming up with a good Internal Assessment (IA) idea.
It's got to be something suitably demanding for diploma-level study, it's got to be something relevant to the chemistry syllabus, it's got to be something you can't just look up the answer to in a textbook, and crucially, it's got to be a topic the student is personally engaged with.

Many students are unsure how to relate the IB chemistry topics to a real-world situation or problem that they can investigate. To help with this, I've produced a list of chemistry IA ideas, together with some example Research Questions (RQ).

I've grouped them together according to the main experimental technique or measurement method.

A big fat disclaimer

This is a list of ideas only, intended as a source of inspiration for students who are stuck for an idea.

It is a starting point for further research, not a list of off-the-shelf projects you can select from and take to your teacher.
Please do not just copy directly from this list!
There are several reasons why you shouldn't do this:

Firstly, one of the internal assessment criteria is Personal Engagement. This is about how well you engage with the project and make it your own.

To achieve the maximum score "The evidence of personal engagement with the exploration is clear with significant independent thinking, initiative or creativity. The justification given for choosing the research question and/or the topic under investigation demonstrates personal significance, interest or curiosity. There is evidence of personal input and initiative in the designing, implementation or presentation of the investigation."

It should be clear from these guidelines that you need to choose your own project and completely own it.

Secondly, some of the projects below are just plain bad for reasons I've outlined in my post about research questions.

These reasons include:

The RQ is just a title

The RQ is unfocused and unclear - impossible to understand what the aims are

The RQ doesn't include any variables

Project is unimaginative

Project has obvious outcomes

Project is just a series of measurements or a synthesis, rather than an investigation

I've given a weaker and a stronger example research question for each category, but be aware that the stronger research question is not necessarily a good research question.

With that out of the way, here's the list:

# data[].attributes.attachment_link.title
IB Chemistry IA Ideas and Research Questions

# data[].attributes.attachment_link.description
50+ Chemistry IA Ideas with Research Question ExamplesOne of the biggest challenges facing students taking IB chemistry is coming up with a good Internal Assessment (IA) idea.It's got to be something suitably demanding for diploma-level study, it's got to be something relevant to the chemistry syllabus, it's got to be

# data[].attributes.attachment_link.readable_text
Fuel cells have to be supplied by an external source of fuel (e.g. hydrogen) and an oxidant e.g. oxygen or air.

The hydrogen or any other fuel is oxidised electrochemically inside the fuel cell to produce a potential difference i.e. a voltage capable of producing a working current.

The overall chemical reaction in a hydrogen fuel electrochemical cell involves the oxidation of hydrogen by oxygen to produce only water.

Hydrogen fuel cells offer an alternative to rechargeable cells and batteries.

A fuel cell will produce a potential difference ('voltage') and a workable electric current until one of the reactants is used up.

Hydrogen gas can be used as fuel .

It burns with a pale blue flame in air reacting with oxygen to be oxidised to form water.

A hydrogen-oxygen fuel cell is a non-polluting clean fuel since the only combustion product is water.

Fuel cells do not produce pollutants like carbon monoxide, sulfur dioxide and nitrogen oxides - gases you get from fossil fuel combustion in power stations or burnt road vehicles..

Cars powered by fuel cells would be quite an environmental advantage in cities, where electric cars are already beginning to be significantly used in developed countries.

Fuel cells could replace larger batteries which are not easily recycled and contain highly toxic metal compounds.

It would be an ideal fuel on this basis e.g. for motor vehicles, but that's not the only factor to consider!

It would be ideal if the hydrogen fuel could be manufactured by electrolysis of water e.g. using solar cells.

Hydrogen can be used to power fuel cells.

It all sounds wonderful BUT, still technological problems to solve for large scale manufacture and distribution of 'clean' hydrogen gas or use in generating electricity AND its rather an inflammable explosive gas!

See and fuel survey alternative fuels like biofuels

Fuel cells are 'battery systems' in which two reactants can be continuously fed in .

They must undergo an oxidation-reduction (redox) reaction.

The consequent redox chemistry produces a working current e.g. hydrogen, ethanol and hydrocarbons can be oxidised with oxygen in a fuel cell, rather than conventional combustion.

Fuel cells have the big advantage of not requiring charging up, as long as you keep on supplying the fuel and oxidant.

The motor vehicle industry is looking at fuel cell cars, but lately electric cars with better quality modern battery technology and convenient charging facilities seem to be more in the news.

Plus points in favour of using fuel cells in cars and other road vehicles - advantages

Fuel cells do not produce the usual pollutants like sulfur oxides (acid rain), nitrogen oxides and carbon monoxide (harmful gases from traffic pollution).

Unless an organic fuel like a hydrocarbon or an alcohol is used, there will be no greenhouses gases like carbon dioxide, because hydrogen combustion only produces harmless water.

Fuel cells could be used in countries with little oil and make them less dependant on costly imported oil.

Hydrogen-oxygen fuel cells create water and since the hydrogen will have to be made from abundant water supplies in the long run, it is effectively a renewable resource, unlike fossil fuels like petrol or diesel.

Fuel cells are much more efficient than fossil fuel power stations or costly chemical batteries etc. because the electrical energy is generated directly from the chemical reaction.

In fossil fuel power stations, motor vehicles, coal/gas fires etc. too much energy is lost as waste heat.

Fossil fuels are a finite supply, whereas if we can get hydrogen from water, and the air has lots of oxygen, there is effectively, if not practical at the moment, an infinite supply of fuel.

With a fuel cell there are fewer stages in producing the useful electrical energy, so there is less chance of losing useful energy e.g. waste heat, friction from moving parts etc.

Maybe in the long-run we can get rid of polluting fossil fuelled road vehicles and batteries containing harmful chemicals e.g. toxic metal compounds of cadmium.

Although current electric cars are improving in the design, the batteries are very costly can only be recharged a limiting number of times before requiring replacement. Batteries also store less energy than fuel cells (which still have to be 're-fuelled').

.AND fuel cells have found use in spacecraft (e.g. space shuttle), satellites and orbiting space stations.

Fuel cells can provide a convenient source of electrical power in the space industry.

Fuel cells can be made reasonably lightweight and compact saving both space and weight.

Hydrogen and oxygen may be used from the fuel tanks of spacecraft.

Fuel cells do not have moving parts which could go wrong.

The final product is water, which could be used as drinking water, reducing the initial payload in the spacecraft.

Since water is the only product from a hydrogen-oxygen fuel cell, there are no waste pollution products to deal with.

Issues over the use of fuel cells in transport systems or as a major energy resource - disadvantages

Fuel cells cannot be used for large-scale energy production, so conventional fossil fuel or nuclear power stations still have an important future.

Hydrogen is a gas and requires a much larger storage volume compared to fossil fuels like petrol.

Safe storage is an issue, especially as it would be stored under high pressure to decrease the storage space required.

There is no efficient means of mass producing hydrogen.

Efficient large scale technology is not yet developed to produce hydrogen on a large scale eg from electrolysis using solar power electricity - photovoltaic power system, wind turbines or hydroelectric power.

Although water is cheap and plentiful, it requires expensive electrical energy to electrolyse water to split it into hydrogen and oxygen.

Electrolysis of acidified water is expensive because electricity is expensive and much is still made from fossil fuels. You would need large scale electrolysis plants and then devise safe means of storing and delivering the hydrogen gas to where its needed.

Not only that, most electricity in the world is generated from burning fossil fuels!

Most hydrogen used in industry is made from fossil fuel hydrocarbons, which won't last forever. (see making hydrogen for the Haber Synthesis of ammonia).

Apart from the fact that the electrode catalysts are costly, disposing of used cells has its problems e.g. may contain toxic metal compounds.

More on h ydrogen's potential use in fuel and energy applications includes powering vehicles, running turbines or fuel cells to produce electricity, and generating heat and electricity for buildings and very convenient for remote and compact situations like the space shuttle.

Fuel cells were developed in the 1960s as part of the USA NASA's space exploration programme to provide electrical power.

Fuel cells were/are used in lunar landing vehicles, space stations orbiting the Earth etc.

They are more practical and robust than solar cell panels and definitely safer than small nuclear power units.

When hydrogen is the fuel, the product of its oxidation is water, so this is potentially a clean non-polluting and non-greenhouse gas? fuel.

Most fuel cells use hydrogen, but alcohols and hydrocarbons can be used.

A fuel cell works like a battery but does not run down or need recharging as long as the 'fuel' supply is there.

It will produce electricity and heat as long as fuel (hydrogen) is supplied.

Notes based on the DIAGRAMS and the CHEMISTRY of a hydrogen-oxygen fuel cell

A typical acid fuel cell (above) consists of two electrodes consisting of a negative electrode (or anode) and a positive electrode (or cathode) which are sandwiched around an electrolyte (conducting salt/acid/alkali solution of free ions).

Hydrogen (or other fuel) is fed to the (-) anode, and oxygen is fed to the (+) cathode.

The platinum catalyst activates the hydrogen atoms/molecules to separate into protons (H⁺) and electrons (e ⁻), which take different paths to the (+) cathode.

The electrons go through an external circuit, creating a flow of electricity e.g. to light a bulb.

The protons ( H⁺) migrate through the electrolyte and pass through the semi-permeable membrane to the cathode, where they and electrons reduce the oxygen to water.

In both acid or alkaline hydrogen-oxygen fuel cells, oxygen is the oxidising agent (oxidant, gets reduced) and hydrogen (fuel, gets oxidised) is the reducing agent.

The hydrogen is fed into the anode compartment and the oxygen into the cathode compartment.

The oxidation of the fuel (hydrogen) at the anode electrode provides electrons that flow round (via some device e.g. bulb, motor etc.) to the cathode electrode to effect the reduction of the oxygen.

So you have simultaneous oxidation and a reduction, therefore overall a redox reaction.

In an alkaline hydrogen-oxygen fuel cell, the construction is quite similar, but it is hydroxide ions (OH ⁻) that migrate in the potassium hydroxide solution electrolyte.

Each cell only produces a small voltage (typically 0.4 to 1.0V) so many cells have to be put together in series to give a bigger working voltage.

Note on reverse reaction water ==> hydrogen + oxygen

If there is spare electricity from another source available, you can run the fuel cell in reverse and electrolyse the water to make hydrogen and oxygen (acting as an electrolyser).

The two gases are stored, and when extra electricity or heat needed, the fuel cell can then be re-run using the stored gaseous fuel.

This is called a regenerative fuel cell system.

You can use solar energy from external panels on the space shuttle to do this, and use the fuel during the 'darkness of night'.

Chemical descriptions of hydrogen-oxygen fuel cell

In the electrode equations I have included the 'subscripted' state symbols (aq), (g) and (l) where appropriate.

Example 1.

This acid hydrogen-oxygen fuel cell uses costly platinum electrodes and an acid electrolyte such as phosphoric acid, H₃PO₄ (diagram on right for an acid hydrogen-oxygen fuel cell lighting a bulb)

The electrode equations for an acid hydrogen-oxygen fuel cell are ...

1. oxidation electrode half-equation, hydrogen atoms/molecules lose electrons

2H2(g) ==>4H⁺(aq) + 4e⁻ (half cell equation for the negativeanode electrode*)
or 2H2(g) - 4e⁻ ==> 4H⁺(aq)

electrode equation 1. has been doubled up to balance the electrons involved and so that 1. + 2. equals the overall 'normal' molecular equation for the hydrogen fuel consumption.

2. reduction electrode half-equation, oxygen atoms/molecules gain electrons

O2(g) + 4H⁺(aq) + 4e⁻ ==> 2H₂O(l) (half cell equation for the positive cathode electrode*)

Adding the two electrode equations 1 + 2 gives the overall equation, which is the same as the normal combustion equation, in a way its a sort of 'cooler' combustion without the flame!

2H2(g) + O2(g) ==> 2H₂O(l)

* Note the +ve and -ve electrode charges are reversed compared to electrolysis, because the system is operating in the opposite direction. But, as in electrolysis, you still get reduction at the cathode and oxidation at the anode.
Example 2.
You can also run a hydrogen-oxygen fuel cell with an alkaline electrolyte [e.g. potassium hydroxide solution, KOH(aq)], but still with costly electrodes

In the case of the alkaline hydrogen-oxygen fuel cell the different electrode equations are ...

1. oxidation electrode half-equation, hydrogen atoms/molecules lose electrons, to give hydrogen ions which immediately combine with the hydroxide ions to form water.

2H2(g) + 4OH⁻(aq) - 4e⁻ ==> 4H₂O(l) (oxidation at theanode)
or 2H2(g) + 4OH⁻(aq) ==> 4H₂O(l) + 4e⁻

2. reduction electrode half-equation, oxygen atoms/molecules gain electrons and in combination with water molecules are reduced to hydroxide ions.

O2(g) + 2H₂O(l) + 4e- ==> 4OH⁻ (aq) (reduction at the cathode)

Again, the overall equation is same as the normal combustion equation by adding equations 1. and 2. together.

2H2(g) + O2(g) ==> 2H₂O(l)

Example 3 for more advanced level chemistry students

The diagram on the right shows the same arrangement for a fuel cell, as for hydrogen, but you can use an organic fuel like an alcohol e.g. ethanol ( C₂H₅OH) or methanol ( CH₃OH), which burn exothermally if ignited, but here made to release their chemical potential energy as electrical energy.

The overall cell reactions are ...

C₂H₅OH + 3O₂==> 2CO₂ + 3H₂O + energy

CH₃OH + ³/₂O₂==> CO₂ + 2H₂O + energy

For more details click on the Redox 3 link below

See also 10. Simple cells (batteries)

TOP OF PAGE

Other notes on ADVANCED chemistry pages:

Alkaline hydrogen-oxygen fuel cell is described in Equilibria Part 7 Redox Chemistry

and organic fuel cells are described in Redox Chemistry Part 3.
Electrolysis Quiz (GCSE 9-1 HT Level (harder) Electrolysis Quiz (GCSE 9-1 FT Level (easier)

# data[].attributes.attachment_link.title
hydrogen-oxygen fuel cells advantages disadvantages issues electrode equations how do they work? gcse chemistry KS4 science igcse O level revision notes

# data[].attributes.attachment_link.description
introduction to electrolysis explaining which liquids conduct and why can some liquids conduct electricity and others cannot? - electrolytes, electrodes, what happens on electrode surfaces, the products of electrolysis. There are tables of electrode reactions, descriptions of experimental methods of electrolysis and a summary table of the electrolysis products from many common melts or aqueous solutions that undergo electrolysis when a d.c.

# data[].attributes.attachment_link.title
Passive radiative cooling: New material can keep buildings cool without the use of power - TomoNews

# data[].attributes.attachment_link.readable_text
Choose from over 1,000 well tested, ready-to-use experiments designed to help you integrate probeware into your curriculum.

Search Experiments

Experiments from Vernier Lab Books

Select a lab book to see the included experiments.

# data[].attributes.attachment_link.description
Choose from over 1,000 well tested, ready-to-use experiments designed to help you integrate probeware into your curriculum. Search Experiments Select a lab book to see the included experiments.

# data[].attributes.headline
Effect of dish soap on skin. Why does this happen?

# data[].attributes.subject
Effect of dish soap on skin. Why does this happen?

# data[].attributes.headline
Muscle cramps, why we drink water and why there's acid

# data[].attributes.subject
Muscle cramps, why we drink water and why there's acid

# data[].attributes.body
https://www.youtube.com/watch?v=P3UCnFS8G-o

# data[].attributes.attachment_link.description
Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

# data[].attributes.attachment_link.description
Explaining the difference between absolute uncertainty, relative uncertainty and percentage uncertainty.

# data[].attributes.body
Terms:
- Flash photolysis
- Stopped-flow spectrophotometry
- Femtochemistry

Questions: How was the rate expression question created? constructed? or discovered?

# data[].attributes.body
Ozone Layer:
- Synthesis and breakdown of ozone layer and how it affects us.

# data[].attributes.body
ACID DEPOSITION
Explore the acidity of rivers and find the concentration needed to neutralize

# data[].attributes.body
controlling the pH of the blood

# data[].attributes.body
- Reversible Redox Reactions --> nickel-hydrogen batteries

# data[].attributes.body
Reversible Redox Reactions

# data[].attributes.body
Activity Series - trend and how it is formed?

# data[].attributes.headline
10 March 2020 - oxidation states; how it relates to different colours of metal salts

# data[].attributes.subject
10 March 2020 - oxidation states; how it relates to different colours of metal salts

# data[].attributes.body
The change in oxidation states and how it relates to a change in colour, how does this happen?

From website:
Due to UV absorption of the molecules within the electron. Orgel Diagram and Tanabe-Sugano diagram

# data[].attributes.body
PLANNING DOC:https://docs.google.com/document/d/1vwjeD9V2nJV7aVzIMuL6wKBtQmGLAZhyFa8DygJ0Mug/edit

FOLDER:https://drive.google.com/drive/folders/1wOpCfpGKXaVaQGHOkiTu94wDbpO9oqF2

RUBRIC:https://drive.google.com/open?id=1q0kkk7vVHJGv1ROJYg0HsQm-szYj75e1

# data[].attributes.attachment_link.readable_text
Let's remind ourselves a little bit of what we already know about orbitals and I've gone over this early on in the regular chemistry playlist. Let's say that this is the nucleus of our atom, super small, and around that we have our first orbital, the 1s orbital. The 1s orbital, you can kind of just view it as a cloud around the nucleus. So you have your 1s orbital and it can fit two electrons, so the first electron will go into the 1s orbital and then the second electron will also go into the 1s orbital. For example, hydrogen has only one electron, so it would go into 1s. Helium has one more, so that will also go into the 1s orbital. After that is filled, then you move onto the 2s orbital. The 2s orbital, you can view it as a shell around the 1s orbital, and all of these, you can't really view it in our conventional way of thinking. You can kind of view it as a probability cloud of where you might find the electrons. But for visualization purposes, just imagine it's kind of a shell cloud around the 1s orbital. So imagine that it's kind of a fuzzy shell around the 1s orbital, so it's around the 1s orbital, and your next electron will go there. Then the fourth electron will also go there, and I drew these arrows upward and downward because the first electron that goes into the 1s orbital has one spin and then the next electron to go into 1s orbital will have the opposite spin, and so they keep pairing up in that way. They have opposite spins. Now, if we keep adding electrons, now we move to the 2p orbitals. Actually, you can view it as there are three 2p orbitals and each of them can hold two electrons, so it can hold a total of six electrons in the 2p orbitals. Let me draw them for you just so you can visualize it. So if we were to label our axis here, so think in three dimensions. So imagine that that right there is the x-axis. Let me do this in different colors. Let's say that this right here is our y-axis and then we have a z-axis. I'll do that in blue. Let's say we have a z-axis just like that. You actually have a p orbital that goes along each of those axes. So you could have your two-- let me do it in the same color. So you have your 2p sub x orbital, and so what that'll look like is a dumbbell shape that's going in the x-direction. So let me try my best attempt at drawing this. It's a dumbbell shape that goes in the x-direction, in kind of both directions, and it's actually symmetric. I'm drawing this end bigger than that end so it looks like it's coming out at you a little bit, but let me draw it a little bit better than that. I can do a better job. And maybe it comes out like that. Remember, these are really just probability clouds, but it's helpful to kind of visualize them as maybe a little bit more things that we would see in our world, but I think probability cloud is the best way to think about it. So that is the 2px orbital, and then I haven't talked about how they get filled yet, but then you also have your 2py orbital, which'll go in this axis, but same idea, kind of a dumbbell shape in the y-direction, going in both along the y-axis, going in that direction and in that direction. Then, of course, so let me do this 2py, and then you also have your 2pz, and that goes in the z-direction up like that and then downwards like that. So when you keep adding electrons, the first-- so far, we've added four electrons. If you add a fifth electron, you would expect it to go into the 2px orbital right there. So even though this 2px orbital can fit two electrons, the first one goes there. The very next one won't go into that one. It actually wants to separate itself within the p orbital, so the very next electron that you add won't go into 2px, it'll go into 2py. And then the one after that won't go into 2py or 2px, it'll go into 2pz. They try to separate themselves. Then if you add another electron, if you add-- let's see, we've added one, two, three, four, five, six, seven. If you add an eighth electron, that will then go into the 2px orbital, so the eighth electron would go there, but it would have the opposite spin. So this is just a little bit of review with a little bit of visualization. Now, given what we just reviewed, let's think about what's happening with carbon. Carbon has six electrons. Its electron configuration, it is 1s2, two electrons in the 1s orbital. Then 2s2, then 2p2, right? It only has two left, because it has a total of six electrons. Two go here, then there, then two are left to fill the p orbitals. If you go based on what we just drew and what we just talked about here, what you would expect for carbon-- let me just draw it out the way I did this. So you have your 1s orbital, your 2s orbital, and then you have your 2px orbital, your 2py orbital, and then you have your 2pz orbital. If you just go straight from the electron configuration, you would expect carbon, so the 1s orbital fills first, so that's our first electron, our second electron, our third electron. Then we go to our 2s orbital, That fills next, third electron, then fourth electron. Then you would expect maybe your fifth electron to go in the 2px. We could have said 2py or 2z. It just depends on how you label the axis. But you would have your fifth electron go into one of the p orbitals, and then you would expect your sixth to go into another. So you would expect that to be kind of the configuration for carbon. And if we were to draw it-- let me draw our axes. That is our y-axis and then this is our x-axis. Let me draw it a little bit better than that. So that is the x-axis and, of course, you have your z-axis. You have to think in three dimensions a little bit. Then you have your z-axis, just like that. So first we fill the 1s orbital, so if our nucleus is sitting here, our 1s orbital gets filled with two electrons. You can imagine that as a little cloud around the nucleus. Then we fill the 2s orbital and that would be a cloud around that, kind of a shell around that. Then we would put one electron in the 2px orbital, so one electron would start kind of jumping around or moving around, depending how you want to think about it, in that orbital over there, 2px. Then you'd have the next electron jumping around or moving around in the 2py orbital, so it would be moving around like this. If you went just off of this, you would say, you know what? These guys, this guy over here and that guy over there is lonely. He's looking for a opposite spin partner. This would be the only places that bonds would form. You would expect some type of bonding to form with the x-orbitals or the y-orbitals. Now, that's what you would expect if you just straight-up kind of stayed with this model of how things fill and how orbitals look. The reality of carbon, and I guess the simplest reality of carbon, is if you look at a methane molecule, is very different than what you would expect here. First of all, what you would expect here is that carbon would probably-- maybe it would form two bonds. But we know carbon forms four bonds and it wants to pretend like it has eight electrons. Frankly, almost every atom wants to pretend like it has eight electrons. So in order for that to happen, you have to think about a different reality. This isn't really what's happening when carbon bonds, so not what happens when carbon bonds. What's really happening when carbon bonds, and this will kind of go into the discussion of sp3 hybridization, but what you're going to see is it's not that complicated of a topic. It sounds very daunting, but it's actually pretty straightforward. What really happens when carbon bonds, because it wants to form four bonds with things, is its configuration, you could imagine, looks more like this. So you have 1s. We have two electrons there. Then you have your 2s, 2px, 2py and 2pz. Now what you can imagine is it wants to form four bonds. It has four electrons that are willing to pair up with electrons from other molecules. In the case of methane, that other molecule is a hydrogen. So what you could imagine is that the electrons actually-- maybe the hydrogen brings this electron right here into a higher energy state and puts it into 2z. That's one way to visualize it. So this other guy here maybe ends up over there, and then these two guys are over there and over there. Now, all of a sudden, it looks like you have four lonely guys and they are ready to bond, and that's actually more accurate of how carbon bonds. It likes to bond with four other people. Now, it's a little bit arbitrary which electron ends up in each of these things, and even if you had this type of bonding, you would expect things to bond along the x, y, and z axis. The reality is, the reality of carbon, is that these four electrons in its second shell don't look like they're in just-- the first one doesn't look like it's just in the s orbital and then the p and y and z for the other three. They all look like they're a little bit in the s and a little bit in the p orbitals. Let me make that clear. So instead of this being a 2s, what it really looks like for carbon is that this looks like a 2sp3 orbital. This looks like a 2sp3 orbital, that looks like a 2sp3 orbital, that looks like a 2sp3 orbital. They all look like they're kind of in the same orbital. This special type of-- it sounds very fancy. This sp3 hybridized orbital, what it actually looks like is something that's in between an s and a p orbital. It has a 25% s nature and a 75% p nature. You can imagine it as being a mixture of these four things. That's the behavior that carbon has. So when you mix them all, instead of having an s orbital, so if this is a nucleus and we do a cross-section, an s orbital looks like that and the p orbital looks something like that in cross-section. So this is a an s and that is a p. When they get mixed up, the orbital looks like this. An sp3 orbital looks something like this. This is a hybridized sp3 orbital. Hybrid just means a combination of two things. A hybrid car is a combination of gas and electric. A hybridized orbital is a combination of s and p. Hybridized sp3 orbitals are the orbitals when carbon bonds with things like hydrogen or really when it bonds with anything. So if you looked at a molecule of methane, and people talk about sp3 hybridized orbitals, all they're saying is that you have a carbon in the center. Let's say that's the carbon nucleus right there. And instead of having one s and three p orbitals, it has four sp3 orbitals. So let me try my best at drawing the four sp3 orbitals. Let's say this is the big lobe that is kind of pointing near us, and then it has a small lobe in the back. Then you have another one that has a big lobe like that and a small lobe in the back. Then you have one that's going back behind the page, so let me draw that. You can kind of imagine a three-legged stool, and then its small lobe will come out like that. And then you have one where the big lobe is pointing straight up, and it has a small lobe going down. You can imagine it as kind of a three-legged stool. One of them is behind like that and it's pointing straight up, So a three-legged stool with something-- it's kind of like a tripod, I guess is the best way to think about it. So that's the carbon nucleus in the center and then you have the hydrogens, so that's our carbon right there. Then you have your hydrogens. You have a hydrogen here. A hydrogen just has one electron in the 1s orbital, so the hydrogen has a 1s orbital. You have a hydrogen here that just has a 1s orbital. It has a hydrogen here, 1s orbital, hydrogen here, 1s orbital. So this is how the hydrogen orbital and the carbon orbitals get mixed. The hydrogens 1s orbital bonds with-- well, each of the hydrogen's 1s orbital bonds with each of the carbon's sp3 orbitals. Just so you get a little bit more notation, so when people talk about hybridized sp3 orbitals, all they're saying is, look, carbon doesn't bond. Once carbon-- this right here is a molecule of methane, right? This is CH4, or methane, and it doesn't bond like you would expect if you just want with straight vanilla s and p orbitals. If you just went with straight vanilla s and p orbitals, the bonds would form. Maybe the hydrogen might be there and there, and if it had four hydrogens, maybe there and there, depending on how you want to think about it. But the reality is it doesn't look like that. It looks more like a tripod. It has a tetrahedral shape. The best way that that can be explained, I guess the shape of the structure, is if you have four equally-- four of the same types of orbital shapes, and those four types of orbital shapes are hybrids between s's and p's. One other piece of notation to know, sometimes people think it's a very fancy term, but when you have a bond between two molecules, where the orbitals are kind of pointing at each other, so you can imagine right here, this hydrogen orbital is pointing in that direction. This sp3 orbital is pointing that direction, and they're overlapping right around here. This is called a sigma bond, where the overlap is along the same axis as if you connected the two molecules. Over here, you connect the two molecules, the overlap is on that same axis. This is the strongest form of covalent bonds, and this'll be a good basis for discussion maybe in the next video when we talk a little bit about pi bonds. The big takeaway of this video is to just understand what does it mean? What is an sp3 hybridized orbital? Nothing fancy, just a combination of s and p orbitals. It has 25% s character, 75% p character, which makes sense. It's what exists when carbon forms bonds, especially in the case of methane. That's what describes it's tetrahedral structure. That's why we have an angle between the various branches of a 109.5 degrees, which some teachers might want you know, so it's useful to know. If you take this angle right here, 109.5, that's the same thing as that angle, or if you were to go behind it, that angle right there, 109.5 degrees, explained by sp3 hybridization. The bonds themselves are sigma bonds. The overlap is along the axis connecting the hydrogen.

# data[].attributes.attachment_link.title
sp3 hybridized orbitals and sigma bonds (video) | Khan Academy

# data[].attributes.attachment_link.description
Let's remind ourselves a little bit of what we already know about orbitals and I've gone over this early on in the regular chemistry playlist. Let's say that this is the nucleus of our atom, super small, and around that we have our first orbital, the 1s orbital.

# data[].attributes.attachment_link.readable_text
If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# data[].attributes.attachment_link.title
Conjugated systems and pericyclic reactions | Khan Academy

# data[].attributes.attachment_link.description
Molecules with conjugation can undergo some interesting and useful reactions! We will be learning about the Diels-Alder reaction, including how to predict the stereochemistry and regiochemistry of the product based on the diene and dienophile.

# data[].attributes.body
Electrochemical Cells:
- electrolysis --> Which factors affect the rate of electrolysis in electroplating cells?
- Is the rate of purification of copper affected by voltage?

# data[].attributes.attachment_link.title
Second Law of Thermodynamics - Sixty Symbols

# data[].attributes.attachment_link.description
Professor Mike Merrifield discusses aspects of the Second Law of Thermodynamics. Referencing the work of Kelvin and Clausius, among others! Professor Merrifield is the Head of the School of Physics and Astronomy at the University of Nottingham.

# data[].attributes.attachment_link.readable_text
The Heisenberg uncertainty principle argues that all atoms in a molecule are constantly in motion (otherwise we would know position and momentum accurately). For molecules, they exhibit three general types of motions: translations (external), rotations (internal) and vibrations (internal). A diatomic molecule contains only a single motion., while polyatomic molecules exhibit more complex vibrations, known as normal modes.

Calculate Number of Vibrational Modes

Degree of freedom is the number of variables required to describe the motion of a particle completely. For an atom moving in 3-dimensional space, three coordinates are adequate so its degree of freedom is three. Its motion is purely translational. If we have a molecule made of N atoms (or ions), the degree of freedom becomes 3N, because each atom has 3 degrees of freedom. Furthermore, since these atoms are bonded together, all motions are not translational; some become rotational, some others vibration. For non-linear molecules, all rotational motions can be described in terms of rotations around 3 axes, the rotational degree of freedom is 3 and the remaining 3N-6 degrees of freedom constitute vibrational motion. For a linear molecule however, rotation around its own axis is no rotation because it leave the molecule unchanged. So there are only 2 rotational degrees of freedom for any linear molecule leaving 3N-5 degrees of freedom for vibration.

The degrees of vibrational modes for linear molecules can be calculated using the formula:

\[3N-5 \label{1}\]

The degrees of freedom for nonlinear molecules can be calculated using the formula:

\[3N-6 \label{2}\]

\(n\) is equal to the number of atoms within the molecule of interest. The following procedure should be followed when trying to calculate the number of vibrational modes:

1. Determine if the molecule is linear or nonlinear (i.e. Draw out molecule using VSEPR). If linear, use Equation \ref{1}. If nonlinear, use Equation \ref{2}

2. Calculate how many atoms are in your molecule. This is your \(N\) value.

3. Plug in your \(N\) value and solve.

Example \(\PageIndex{1}\): Carbon dioxide

How many vibrational modes are there in the linear \(CO_2\) molecule ?

Answer

There are a total of \(3\) atoms in this molecule. It is a linear molecule so we use Equation \ref{1}. There are \[3(3)-5 = 4 \nonumber\] vibrational modes in \(CO_2\).

Would CO ₂ and SO ₂ have a different number for degrees of vibrational freedom? Following the procedure above, it is clear that CO ₂ is a linear molecule while SO ₂ is nonlinear. SO ₂ contains a lone pair which causes the molecule to be bent in shape, whereas, CO ₂ has no lone pairs. It is key to have an understanding of how the molecule is shaped. Therefore, CO ₂ has 4 vibrational modes and SO ₂ has 3 modes of freedom.

Would CO ₂ and SO ₂ have a different number for degrees of vibrational freedom? Following the procedure above, it is clear that CO ₂ is a linear molecule while SO ₂ is nonlinear. SO ₂ contains a lone pair which causes the molecule to be bent in shape, whereas, CO ₂ has no lone pairs. It is key to have an understanding of how the molecule is shaped. Therefore, CO ₂ has 4 vibrational modes and SO ₂ has 3 modes of freedom.

References

1. Harris, Daniel C., and Michael D. Bertolucci. Symmetry and Spectroscopy: an Introduction to Vibrational and Electronic Spectroscopy. New York: Dover Publications, 1989. Print.

2. Housecroft, Catherine E., and Alan G. Sharpe. Inorganic Chemistry. Harlow: Pearson Education, 2008. Print.

# data[].attributes.attachment_link.title
Number of Vibrational Modes in a Molecule

# data[].attributes.attachment_link.description
The Heisenberg uncertainty principle argues that all atoms in a molecule are constantly in motion (otherwise we would know position and momentum accurately). For molecules, they exhibit three general types of motions: translations (external), rotations (internal) and vibrations (internal). A diatomic molecule contains only a single motion., while polyatomic molecules exhibit more complex vibrations, known as normal modes.

# data[].attributes.attachment_link.description
Start studying Option B - Biochemistry. Learn vocabulary, terms, and more with flashcards, games, and other study tools.