3.1.1 Atomic Structure

Atomic Structure

Definition of relative atomic mass:

The average mass of an element compared to 1/12th of a carbon-12 atom.

Definition of Isotopes:

A variation of an element that has the same number of protons but different number of neutrons

Subatomic Particles

Particle	Charge	Mass (u)	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	-1	1/1840	Shells

Atomic Models

1. John Dalton - Invisible sphere

2. JJ Thompson - Plum Pudding

3. Ernest Rutherford - Nuclear model

4. Niels Bohr - Bohr model

5. Erwin Schrödinger - Shrodingers’ model

Electron arrangement:

1. Shells

2. Sub-shells

3. Orbitals

4 types of sub-shells

S,P,D,F

Rules for orbitals:

1. Orbitals of lower energy filled first

2. Sub orbitals off the same energy fill singly first then double up

3. 2 electrons in each orbital

Definition of Ionisation energy(kJmol-1):

The energy required to remove one mole of an electron from one mole of a gaseous atom.

Formula for Ionisation energy:

Element(g) → Element⁺(g) + e^-

Formula for ionisation energy electron impact:

Element(g)+ e^-→ Element⁺(g) + 2e^-

Formula for ionisation energies electrospray:

Element(g)+ H⁺(g) → ElementH(g)

Successive Ionisation Energies:

1. Endothermic reaction to overcome electrostatic attraction

2. Each IE is larger than the last as there is stronger electrostatic attraction closer to the nucleus

Trends in the periodic table (Down the group):

1. IE decreases

2. Greater shielding

3. Weaker electrostatic attraction

4. Nuclear charge increases (no. of protons)

Trends in the periodic table (Across a period):

1. IE Increases

2. Shielding stays the same

3. Stronger electrostatic attraction

4. Nuclear charge increases (no. of protons)

Stages of Mass spectroscopy:

1. Ionisation - Electron impact (fired from an electron needle)/ Electrospray (Has to be vapourised in water or methanol first)

2. Acceleration - Electric fiield

3. Separation of charged ions - Enter the flight tube (ion drift)

4. Detection - Ions hit the plate, calculating TOF

TOF Formulas:

v = d/t and E_k = ½ mv²