Atomic Structure/ Fundamental Particles

AQA A Level Chemistry AS Physical

electron relative mass

1/1836

Z

atomic/ proton number

A

mass/ nucleon number

isotopes

atoms of the same element that contain the same number of protons and electrons but different number of neutrons, causing them to have different physical properties

nucleons

protons and neutrons held together in the nucleus by strong nuclear force

formula for number of electrons

e- = 2n2

atomic orbital

particular volume of space on an energy level

order of atomic orbitals

1s 2s 2p 3s 3p 4s 3d

factors that affect energy in energy levels

distance from nucleus, shielding, relative nuclear charge (number of protons)

transition metal atomic orbital rules

fills 4s before 3d, in ions remove electrons from 4s before 3d

chromium electron configuration

3d⁵4s¹

copper electron configuration

3d¹⁰4s¹

ionisation energy

the enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms

first ionisation energy

the enthalpy change when 1 electron is removed from a gaseous atom

second ionisation energy

the enthalpy change when a 2nd electron is removed from a 1+ ion

third ionisation energy

the enthalpy change when a 3rd electron is removed from a 2+ ion

why ionisation energy increases across a period

increased nuclear charge, decreased atomic radius, more outer electrons in same energy level

why ionisation energy decreases down a group

atomic radius increases, shielding increases

mass spectrometer

instrument that measures the mass of atoms and molecules to identify an element

Ar

relative atomic mass/ average mass of 1 atom relative to 1/12 mass of carbon-12 atom

Mr

relative molecular mass/ average mass of 1 molecule relative to 1/12 mass of carbon-12 atom

mass spectrometry process

1. vaporisation in a vacuum

2. ionisation into positive ions

3. acceleration to the same kinetic energy

4. drift over a fixed distance

5. detection at a negative plate

ionisation methods

electron spray and electron gun

electron gun process

gaseous sample is injected into a flight tube where electrons are being fired from a hot filament to a positive plate across the rube, these electrons knock an electron off the sample

electron spray

sample is dissolved in a volatile solvent and then forced through a needle while a high voltage is applied, causing the sample to gain a proton

electron gun equation

X(g) → X+(g) + e-

electron spray equation

X + H+ → XH+

mass spectrometer detection

lightest positive ions arrive first and gain electrons from the negative plate which causes a current to flow, the greater the abundance the greater the current generated

Aufbau Principle

electrons enter lowest energy orbital possible

Hund’s rule

electrons occupy orbitals alone and only pair when no empy orbitals are available in the same energy level

degenerate orbitals

orbitals in the same sub shell that have the same energy

why are chromium and copper exceptions to 4s rule?

these configurations are energetically stable