Unit 1: Section 1 - Atomic Structure

The average mass of an atom of an element on a scale where an atom of carbon-12 is 12 (an average, so not usually a whole number)

The number of protons and neutrons

Protons - +1 1 Neutrons - 0 1 Electrons - -1 1/2000

Mass number - A Atomic number - Z

The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12 (usually a whole number)

The average mass of a molecule on a scale where an atom of carbon-12 is 12

Relative atomic mass, relative molecular mass, relative isotopic abundance and to identify elements

• Ionisation • Acceleration • Ion drift • Detection

• Electrospray ionisation • Electron impact ionisation

• The sample is dissolved and pushed through a small nozzle at high pressure • A high voltage is applied to it, causing each particle to gain an H+ ion

• 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

• Electric field accelerates positively charged ions • All have the same kinetic energy • Lighter ions travel faster than heavier ions

The ions enter a region with no electric field, so they just drift through it (lighter ions will drift through faster than heavier ions)

• Because lighter ions travel at higher speeds in the drift region, they reach the detector in less time than heavier ions. • The detector detects charged particles, an electrical current is produced in the detector when a charged particle hits it • A mass spectrum is produced

• mass/charge against abundance (often as a percentage) • If the sample is an element, each line will represent a different isotope of that element • If the spectrum was produced using electrospray ionisation, then you have to take away one from the m/z ratio to get the relative mass of each isotope

• For each peak read the % relative isotopic abundance from the y- axis and the relative isotopic mass from the x-axis, and multiply them together to get the total mass for each isotope • Add up these totals • Divide by 100 (percentages were used) • If the relative abundance is not given as a percentage, divide by the sum of the relative abundances instead of 100

They donate one of their 4s electrons to the 3d sub-shell, because they favour a more stable full or half filled d sub-shell

When they become ions, they lose their 4s electrons before their 3d electrons

The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions - endothermic

X(g) → e− + X+(g)

• You must use the gas state symbol because ionisation energies are measured for gaseous atoms • Always refer to 1 mole of atoms rather than 1 singular atom • The lower the ionisation energy, the easier it is to form an ion

• Nuclear charge - the more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons • Distance from nucleus - weaker attraction the further away the electrons are • Shielding - as the number of energy levels between the outer electrons and the nucleus increases, the outer electrons are less attraction towards the nucleus

The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ions to form 1 mole of gaseous 2+ ions

• Within each shell, successive ionisation energies increase, this is because electrons are being removed from an increasingly positive ion - there’s less repulsion amongst the remaining electrons, so they’re held more strongly by the nucleus • The big jumps in ionisation energy happen when a new shell is broken into as an electron is being removed from a shell closer to the nucleus