ATOM , PERIODIC TABLE, PERIODICITY, BONDING - GR10 by Lizelle Swanepoel

HISTORY OF THE ATOM

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The Story of the Atom

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450 B.C. Democritus & Leuciippus of Miletus

They introduces the idea of “atomos” as uncuttable particles.

1803 John Dalton - “Billiard Ball Model”

He re-introduces “atomos” as the term atom; atoms being the smallest particles of matter.

1872 Dimitri Mendeleev - Devised the first Periodic Table

He drew up the first periodic table.

1896 Becquerel, Marie Curie and Pierre Curie - discovered radioactivity

Henry Becquerel and the Curies discovered elements that give off a mysterious radiation. They investigated radioactivity of elements. Unstable elements with an unbalanced number of neutrons to protons are radioactive and can undergo alpha-, beta- and gamma radiation.

1897 J.J. Thomson - Plum Pudding Model

He discovered the electron with cathode ray tubes.

1911 Ernest Rutherford (together with his post-grad students Marsden and
Geiger) - The Nuclear Model

He discovers the nucleus and protons at the centres of atoms, which he calls the nucleus. He says that the nucleus is filled with positive protons and electrons randomly orbiting the nucleus.

1913 Niels Bohr - The Planetary Model

He proposes a Planetary Model for the atom, where electrons move around the nucleus in fixed orbits named energy levels (like planets orbit around the sun).

1913 Louis de Broglie - electron is both wave and particle

1926 Werner Heisenberg & Erwin Schrödinger - The Quantum mechanical model

Heisenberg and Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position, called an orbital. This atomic model is known as the quantum mechanical model of the atom.

1932 James Chadwick - Discovered the neutron

Today - THE STANDARD MODEL
- We know the structure of atoms from smashing atoms together in the LHC (particle accelerator) at CERN and in other big labs across the globe.
- We know that electrons are always in motion around the nucleus.

- Electrons are fundamental particles,

i.e. they cannot be broken into any smaller particles

- Protons and neutrons vibrate within the nucleus.

- Protons and neutrons are not fundamental particles, i.e. they

are made up of smaller particles

- Quarks vibrate within the protons and neutrons.

- Quarks are fundamental particles.

DEMOCRITUS

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JOHN DALTON

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JJ THOMSON

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THOMSON, RUTHERFORD & CHADWICK

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Discoverers of the electron, proton and neutron:

NIELS BOHR

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ERWIN SCHRODINGER

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WERNER HEISENBERG

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TIMELINE SUMMARY

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PROPERTIES OF THE SUB-ATOMIC PARTICLES

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Size of the atom is incredibly small - in range of picometers or 10^-12 m magnitude.
Mass is very small - 1 amu = 1,66 x 10^-27kg
1 H-atom has mas of 1 amu.

Relative atomic mass:

Carbon-12 is used as standard.
All other atoms' mass is based on their mass relative to C-12.
1 H-atom has mass of a twelveth that of C-12
1 Mg atom has mass twice that of C-12

ATOMIC NUMBER AND MASS NUMBER

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Atomic mass

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ISOTOPES

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Isotopes = atoms of an element that have the same number of protons, but differing numbers of neutrons in their nuclei.

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Do a calculation using isotopes to determine the relative atomic mass of an element

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Electron configuration - How electrons fill up energy levels

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Electrons occupy different energy levels in an atom, with specific energy
We say their energy is QUANTISED.
electrons can absorb specific amounts of energy to go from ground state to excited state
they then drop back to lower energy levels after and release specific amounts of energy, emitted as EM radiation of a specific colour
Atomic line spectra are a result of quantisation of energy - specific colours for each unique element
Energy levels shown by principle quantum number n - n = 1,2,3,4 etc
Electrons demonstrates inherent angular momentum = Spin
Electrons have up or down spin:
- Up-spin = 1/2
  Down spin = -1/2
Each E-level holds a maximum of 2n²electrons
Within E-levels electrons occupy areas called orbitals
s, p, d, f orbitals - we will only focus on s and p-orbitals
Each orbital holds 2 electrons at most
s-orb has lower energy than p-orbitals etc
Electrons are assigned to orbitals according to the Aufbau principle
Rules electrons obey to build up an atom:
- Aufbau principal
- Pauli’s Exclusion Principle
- Hund’s Rule (The "empty bus seat rule")

ENERGY LEVEL DIAGRAMS

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Rules that electrons obey to build up an atom

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Aufbau principal = build UP from bottom to top, from lowest energy.
Pauli’s Exclusion Principle = no two electrons in an orbital can have the same spin.
Hund’s Rule = p-orbitals are singly occupied before pairing up. (Empty Bus Seat Rule)

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Order of filling orbitals

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Identify the mistake and rule violated:

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Identify the mistake and rule violated:

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Identify the mistake and rule violated:

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s,p,d,f-blocks in periodic table

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A block of the periodic table is a set of chemical elements having their differentiating electrons predominately in the same type of atomic orbital. ... Each block is named after its characteristic orbital their electrons fill up to: s-block; p-block; d-block; and f-block

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Give definitions of: 1. ORBITAL, 2. ENERGY LEVEL DIAGRAM, 3. HUND'S RULE, 4. THE PAULI EXCLUSION PRINCIPLE

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VALENCY & CORE ELECTRONS

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DEF:

VALENCY = the number of electrons an atom must lose or gain to achieve a filled outermost energy level, to attain its most stable state.

CORE ELECTRONS = the electrons found below the outermost energy level in an atom.

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BONDING - TYPES OF CHEMICAL BONDS

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COVALENT BOND
- A bond that is formed by the overlapping of shells and the sharing of electrons (usually between non-metals).
IONIC BOND
- A bond that is formed by electrostatic attraction between positive and negative ions in a crystal lattice (usually between metal and non-metal).
METALLIC BONDING
- A bond that is formed between positive cations and delocalised electrons in metal crystal structures

METALLIC BONDS

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Metals are made up of a "sea" of delocalised electrons surrounding positive kernels (cations).

THE PERIODIC TABLE OF ELEMENTS

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MECHANISM FOR IONIC BONDING

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MECHANISM FOR COVALENT BONDING

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METALLIC BONDS

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DEFINITIONS

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Intramolecular Bond:

a bond which occurs between atoms within molecules.

Covalent bond:

a bond which occurs due to sharing of at least one pair of electrons by two nonmetal atoms.

Non-polar covalent (pure covalent):

an equal sharing of electrons.

Polar covalent:

an unequal sharing of electrons leading to a dipole forming (as a result of electronegativity difference)

Ionic bond:

a bond which occurs due to a transfer of electrons and subsequent electrostatic attraction.

Metallic bonding:

a bond between positive kernels and a sea of delocalised electrons.

STRUCTURE OF IONIC COMPOUNDS

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FORMATION OF SALTS

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BONDING - PHYSICS SONG

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ACAPELLA SCIENCE

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Worksheet

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Worksheet

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Worksheet

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Worksheet

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EXERCISE

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Do the Aufbau diagrams for the first 20 elements. Use your notes and the diagrams in there to do it on.

WHERE DO ELECTRONS LIVE IN THE ENERGY LEVELS?

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IN ORBITALS.

Shapes of orbitals

The Schrödinger Wave Equation is used to calculate the outside surface of a region of space in which there is a high probability of finding an electron – we can thus visualise the shapes of the orbitals:

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DEFINITIONS

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PERIODIC TABLE & REACTIONS - ADDITIONAL EXERCISES

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PERIODICITY

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PERIODICITY - TRENDS IN THE PERIODIC TABLE

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We look at these trends:

Reactivity
BP and MP
Density
Atom radius
Ion radius
Ionisation energy
Electron affinity
Electronegativity

REACTIVITY

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Reactivity = How quickly an atom can attain a full outermost energy level.

Reactivity increases down a group; for non-metals reactivity decreases down a group.
Nonmetal reactivity decreases down a group, because the nonmetal nucleus' ability to gain more valence electrons weakens due to more nuclear shielding.
Metal reactivity increases down a group. The most reactive metals are those that can lose their valence electrons most easily.

ORDER OF FILLING ORBITALS USING THE AUFBAU PRINCIPLE

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From left to right, from lowest to higher period numbers.
E.g.
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s,4d.....

PERIODIC TRENDS (PERIODICITY)

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IONISATION ENERGY TREND

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DEF:
The amount of energy required to remove an electron from a gaseous atom to form a cation.

Ionisation Energies (IE) for period 1, 2, 3, 4 elements up to Ca

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Ionization Energy Chemistry
Question

Q1. Ionization energy depends upon:

(a) Effect of the arrangement of electrons

(b) Penetration effect of the electrons

(c ) Screening effect of inner electrons

(d) All of the above

Q2. Which of the following elements has the lowest ionization energy?

(a) Barium

(b) Magnesium

(c ) Calcium

(d) Chromium

Q3. Which of the following elements has the highest first ionization energy?

(a) Lithium

(b) Fluorine

(c ) Sodium

(d) None of the above

Electron affinity

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DEF:
The energy change when an electron is added to a gaseous atom to form an anion.
(A measure of ability of an atom to accept an electron)

Outlier:

Chlorine has a higher electron affinity than Fluorine.
That is because although fluorine wants to attract electrons in a bonded pair more easily than chlorine, once it has the electron all to itself (gains an electron) the repulsive forces in the small size of the fluoride ion comes into effect.

ELECTRONEGATIVY

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DEF:
The ability of an atom in a compound to attract bonding electron pairs.

ANIMATION OF IE, EA, EN:

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GIANT STRUCTURES - SAND, DIAMOND, GRAPHITE

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Sand = SiO₂

DIAMOND

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A giant molecule of extremes: high melting point, extreme hardness, and impossible to dissolve.

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DIAMOND VS. GRAPHITE

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GRAPHITE

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Delocalised electrons allow graphite to conduct electricity.

In graphite, each carbon atom uses just 3 of its valence electrons
to form 3 single covalent bonds with 3 other carbon atoms.
The remaining electron is delocalised
and can move about freely through the crystal lattice.
The covalent bonds within each layer are strong,
BUT we can easily overcome the weak intermolecular forces of attraction between layers by applying a small force.
Therefore, graphite is slippery.
Used in lubricants in cars and in pencil "leads".

Noble Gas Configuration

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A noble gas configuration = elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons.

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REACTION OF METAL WITH OXYGEN

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Reactivity - Gr1

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PT😂

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Notes Answers - p3

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