Atomic structure

All atoms of one element are the same and are different from the atoms of another element- atoms are tiny and invisible

The electron

Thomson

The atom is a sphere of positive charge with evenly distributed negative charges

That most of the mass of an atom is concentrated in the positive nucleus with negative electrons orbiting it

Electrons orbit the nucleus at specific distances

Atom consists of a small, dense, central nucleus surrounded by orbiting electrons in electron shells
The nucleus consists of protons + neutrons

1/1840

A

Sum of protons and neutrons in an atom

Z

Number of protons in an atom

Average mass of an atom relative to 1/12 the mass of carbon-12

Atoms of the same element with the same atomic number but a different number of neutrons resulting in a different mass number

Identical- Proton number and electron configuration is the same

Different- different mass numbers

Identifies different isotopes to find the overall atomic mass

Ionisation -> Acceleration to constant KE -> Ion drift -> Ion detection -> Data analysis

- sample needs to be ionised to form positive ions
- allows sample to be accelerated + detected

- electron impact
- electro-spray

The sample is vaporised and an 'electron gun' is used to fire high energy electrons at it. This knocks one electron off each particle, so they become +1 ions.

X+(g) + e- -> X+(g) + 2e-
X(g) -> X+(g) + e-

Substances with low formula mass where the +1 ion is known as a molecular ion

Molecular ion breaks down into fragments

Electron impact ionisation

Samples is dissolved in a volatile solvent and injected through a hypodermic needle to give a fine mist
Tip of needle is attached to a positive terminal of a high voltage power supply
Each molecule gains a proton from solvent as they leave the needle

X(g) + H+ -> XH+ (g)

Substances with a higher Mr

Ions are accelerated using an electric field to the same kinetic energy

Its mass

Ions seperate depending on velocity as they travel towards a negatively charged plate

Less- higher velocity

- Positive ions hit a negatively charged electric plate
- Positive ions gain electrons from the plate
- Generates a movement of electrons and hence an electric current
- Size of electric current gives a measure of the number of ions hitting the plate (abundance)
- Computer uses the data to produce a mass spectrum
-> mass to charge ratio + abundance

The bigger the molecule the more fragments there are

A smaller peak next to the M+ peak caused by the presence of C13 and H2 isotopes in the molecule

Fixed amounts called quanta

principal energy levels

Energy required to remove one mole of electrons from one mole of gaseous atoms

- Atomic radius
- Shielding
- Nuclear charge

Ionisation energy decreases as electrostatic attraction between outer electron and nucleus decreases: increased shielding + atomic radius

Ionisation energy increases as attraction between nucleus and outer electron increases: nuclear charge increases whilst number of shells remains constant

s- 2
p- 6
d- 10
f- 14

Regions of space where an electron is likely to be found

spherical

dumbell

s-1
p-3
d-5
f-7

1- 2
2- 8
3- 18
4- 32

The lowest energy sub levels are occupied first

groups 1 and 2

groups 3-7 + 0

transition metals

lanthanides and actinides

Remove from highest energy level first

Remove from 4s before removing from 3d

- In group 2 the electron is removed from an s sub shell
- In group 3 the electron is removed form a p sub shell
- The p subshell is higher energy than the s sub shell so less energy is required to remove the electron

A property called spin that can be 'up' or 'down'

Opposite spin

Single electrons occupy all empty orbitals before they start to form pairs in orbitals

Repulsion between them due to their negative charges

- In group 5 the electron is removed from a singly occupied p orbital
- In group 6 the electron is removed from a p orbital containing 2 electrons
- There is electron electron repulsion in group 6, making the electron easier to remove

- In each case the 4s orbital only contains 1 electron
- This is because the 4s and 3d subshells lie very close together in energy
- 3d being half full or full is a lower energy arrangement