10CH1E Chemistry Revision by Chris Jurgens

reasons for high melting/boiling points

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- Metals tend to have high melting/boiling points compared to other substances as they have metallic bonds between their valence electrons.

- Metallic bonding is the strong attraction between the closely-packed, positively-charged metal ions and a 'sea' of delocalised electrons.

- The attraction between the positively-charged metal ions and the 'sea' of delocalised electron require the most energy to break apart, therefore a high amount of heat (measured in units of energy) is needed.

Properties of ionic compounds

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Bonding and non-bonding electrons

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In covalent bonding, electrons are shared between atoms. The specific electrons that are shared are called the bonding electrons, while the ones that are not are called non-bonding.

Shapes of covalent molecules

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-Trigonal pyramidal:
three bonds and a valence electron pair (EG: AMMONIA, NH3)
-Tetrahedral
four bonds, equal angles (EG: METHANE, CH4)
-Trigonal planar
three bonds, even angles, flat
-Bent
two bonds and a nonbonding valence electron pair 2D (EG: WATER, H2O)
-Linear
two + bonds, 2D (FLUORINE, F2 or CARBON DIOXIDE, CO2)

Non-metal and Non-metal

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Non-metal and Non-metal

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In a covalent

Non-metal and Non-metal

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In a covalent bond both atoms are non-metals. All atoms that make up the bond want to gain more electrons so they share them.

Intermolecular forces

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London dispersion forces - imbalances in the electron distribution will cause temporary dipoles that attract each other, therefore causing the bond. These forces are the weakest because the bonds are only temporary.
Dipole-dipole - In a dipole-dipole bond, one atom is more electronegative, which means it wants to gain electrons. This makes it more negatively charged, causing the positively charged atom to be attracted to the negatively charged one. This bond has the middle amount of strength out of the three forces.
Hydrogen bonding - When hydrogen bonds to atoms these three atoms that have a high electronegativity, oxygen, fluorine and nitrogen, the hydrogen atom acquires a large amount of positive charge. This is because the atoms that are more electronegative want to gain hydrogen's electrons and therefore make the hydrogen atom more positive. This bond is the strongest of the three intermolecular forces.

Using table of common ions

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Naming molecules (covalent bonding)

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Rule 1: The element with the lower group number is written first in the name; the element with the higher group number is written second in the name. Exception: when the compound contains oxygen and a halogen, the name of the halogen is the first word in the name.
Rule 2: If both elements are in the same group, the element with the higher period number is written first in the name.
Rule 3: The second element in the name is named as if it were an anion, by adding the suffix -ide to the name.
Rule 4: A prefix is used in front of each element name to indicate how many atoms of that element are present. Exception: if there is only one of the first element in the formula, the mono- prefix is dropped. e.g SO₃sulfur trioxide

metal and non

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Metal and non-metal (cation and anion)

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ANION (negatively charged ions)
- Non-metals GAIN electrons to attain a Noble Gas configuration. - They make negative ions (anions)
- Non-metals will have many valence electrons (usually 5 or more)
- They will gain electrons to either fill the outer shell OR bring it to 8 (octet rule).

CATION (positively charged ions)

- Metals LOSE electrons to attain a Noble Gas configuration.
- This creates positive ions called CATIONS.
- Metals have few valence electrons (usually 3 or less).

CATION AND ANION

- All atoms react to try and achieve a Noble Gas configuration.

- Noble gases have 2 ‘s’-shell and 6 ‘p’-shell electrons.

- Their 8 valence electrons makes them stable! (This is the OCTET RULE )

- Anions and Cations are held together by opposite charges (+ and −)

- Electrons are transferred to achieve noble gas configuration in both cation and anion.

Sing

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Single, double and triple Covalent bonds

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- Covalent bonds is sharing an electron between non-metal elements to gain a full outer shell

-Only occurs in non-metal elements
- Doesn't lose or gain electrons
- Sharing electrons only happen with the valence electrons
- When the atoms aren't bonding they're called "lone pairs" or "non-bonding"

2 ways to show a bonding pair:
Lewis structure: is shown with ":"
Structural form: is shown with "-"

SINGLE BOND SHARES 2 ELECTRONS, DOUBLE BOND SHARES 4 ELECTRONS. TRIPLE BOND SHARES 6 ELECTRONS. THERE ARE NO QUADRUPLE BONDS!

Reasons for low melting/boiling points

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- Intermolecular bonds are much weaker than intramolecular bonds (within an atom).
- To melt these substances energy must be transferred during this process which overcomes the attractive forces allowing the molecules to move over each other (changing form - liquid) or moving away from each other (gas).
- The stronger the forces are between the intermolecular forces the higher the melting point. That is why simpler molecules melt more easily as they have weaker intermolecular bonds.

Properties of metals

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For most metals they have certain characteristics, they are solid at room temperature, they have a high melting point, they are good conductors of electricity and heat, they are malleable, they are ductile, they are strong and dense. In a pure metal the atoms are in tightly packed layers and form a lattice structure. SEA OF ELECTRONS SURROUND THE POSITIVE IONIC LATTICE.

Reasons why some molecules have a polarity and create a dipole:

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Within a covalent bond, the more electronegative atom will pull the electron density of the bond closer to itself, giving it a partial negative charge. This leaves the atom with a partial positive charge, which creates a dipole moment making one end permanently negative and the other positive.

Formation of ions

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Between a metal and non-metal. It is a give and take relationship. One is a lover(NON-METAL) and the other is a hater(METAL) which holds the bond together. Metals give while non-metals take in order to attain a noble gas configuration.THE OPPOSITELY CHARGED IONS ATTRACT TOGETHER. THIS IS A STRONG ATTRACTION WHICH IS WHY IONIC SUBSTANCES HAVE HIGH MELTING & BOILING POINTS.

metallic bonding between metal elements

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Bonds between metal elements.
both elements don't want electrons so they shift the electrons between the each atom, creating a bond. the electrons become delocalised (NOT HELD AT ONE POSITION) and the atom receives a motive charge.

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ANION

Properties of ionic compounds

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- They form crystals
- They have high melting and boiling points
- They have higher enthalpies of fusion and vaporisation than molecular compounds
- They're hard and brittle
- They conduct electricity when they are dissolved in water
- They're good insulators

Naming ionic compounds

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1) The number of Cations and Anions in an ionic compound must be equal/balanced to make an electrically neutral molecule (Net Charge must be ZERO)
2) Charges are not specified
3) The cation is written before the anion and undergoes no changes in its name.
4) The ending of the anion is removed and the suffix -ide is substituted.
Example: Mg₃P₂

For this ionic compound, the Magnesium is the cation and therefore has no changes in it's name; the anion is the Phosphorus and therefore the ending is removed and the suffix -ide is substituted. 
= Magnesium Phosphide

Valence electrons across the periodic table:

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GROUP 1 HAS 1 VALENCE ELECTRON, GROUP II HAS 2 AND SO FORTH....
EVERY ELEMENT IN A GROUP HAS THE SAME NUMBER OF VALENCE ELECTRONS, THAT IS WHY THEY REACT AS THEY DO AND EXPLAINS SIMILARITIES IN THEIR CHEMICAL REACTIONS.

Valence electrons across the periodic table

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- Increase across a period
-The amount of valence shell electrons is relevant to it's group number (ie. Hydrogen = Group 1, therefore = 1 valence electron)

Drawing Lewis structures and Valence structure

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Lewis structure
- Has dots for both bonding and non-bonding electrons
Valence structure:
- Lines represent bonding pairs
- Dots represent non bonding/lone pairs of an element

Delocalised Electrons

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Delocalised electrons in a metallic bond are electrons that are not associated with a single atom or a covalent bond. They move freely around the atoms creating a strong bond. They are responsible for many of the properties found in metals:

The high melting point is due to the strong attraction between the electrons
They conduct heat well because of the transfer of heat through the moving electrons
They are strong because the layers of metal ions are able to slide over each other

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chemical formula

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Simplest ratio of elements in an ionic compound is called the FORMULA UNIT or EMPIRICAL FORMULA
chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.
Example： C₆H₁₂O_6，C₅H₁₀O_5，C₂H₄O_2，CH₂O all have different molecular formulas but the same empirical formula: CH₂O.
formula unit is the lowest whole number ratio of ions represented in an ionic compound.

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