chemistry - unit 1 - section 1 : atomic structure

nucleus

most of the mass of an atom and very small. Contains protons and neutrons

electrons

orbits the nucleus in shells and take up most of the space of an atom

protons relative charge

+1

protons relative mass

1

neutrons relative charge

0

neutrons relative mass

1

electrons relative charge

-1

electrons relative mass

1/2000

definition of ions

ions have a different number of electrons and protons

isotope definition

elements with the same number of protons but a different number of neutrons

elements with same atomic number different atomic mass

1803 John Dalton

atoms are spheres and each elements is made from different spheres

1897 J.J Thomson

discovered the electron. the atom wasn’t solid and was made up of other particles. the plum pudding model was developed.

plum pudding model: an atom is a sphere of positive charge with negatively charged electrons in it.

1909 Ernest Rutherford

Discovered the nucleus. Also discovered that the nucleus was a very small and positively charged. He also concluded the atom was mainly empty space made up a negative ‘cloud’.

Gold Leaf Experiment (1909)

positive alpha particles fired at thin gold leaf. most went through the gold leaf (mainly empty space). small number deflected back (they hit a small positive nucleus)

1913 Niels Bohr

discovered a problem with rutherford’s model. the cloud of electrons could collapse into the positive nucleus. He proposed electrons were in fixed energy shells

the experimental proof (1913)

when EM radiation is absorbed, electrons move between shells. They emit this radiation when electrons move down to lower energy shells.

Atomic Model Today

electrons don’t have the same energy in shells. we have subshells. this explains ionisation trends

TOF mass spectrometry - vaporisation

the sample is vapourised so it can travel through the TOF mass spectrometer

TOF mass spectrometry - ionisation

the sample is pushed through the nozzle making a high pressure jet. a high voltage is passed through causing the loss of an electron. A gaseous positively charged sample is produced. we call this electrospray ionisation.

TOF mass spectrometry - acceleration

the positive ions are passed through an electric field. particles with lower mass/charge (m/z) ratio will accelerate quicker

TOF mass spectrometry - ion drift

particles travel through with a constant speed and kinetic energy. they drift through and particles with lower mass/charge (m/z) ratios travel faster

TOF mass spectrometry - detection

ions are detected as electrical current is made when particle hits the plate. particles with lower m/z reach the detector first as they travel fastest

definition of relative atomic mass

the average mass of an atom of an element in comparison to 1/12th mass of a carbon 12 atom

definition of relative molecular mass

the average mass of a molecule in comparison to 1/12th mass of a carbon-12 atom

definition of relative isotopic mass

the average mass of an an atom of an isotope of an element in comparison to 1/12th mass of a carbon-12 atom

m/z (mass/charge) in isotopes in mass spectra

the mass of an isotope divided by charge. asmost have just a +1 charge this is the same as the isotopic mass

m/z (mass/charge) in molecules in mass spectra

m/z is the mass of a fragment divided by charge. as most have just a +1 charge this is the same as there fragment mass

M+ (molecular ion) peak in mass spectra

the peak shows the fragments that hasn’t been broken up. the whole thing has been ionised and the whole molecule has gone through. the value is the same as the relative molecular mass of a molecule

electron configuration: 4 subshells

s - has 1 orbital = 2 electrons

p - has 3 orbitals = 6 electrons

d- has 5 orbitals = 10 electrons

f - has 7 orbitals = 14 electrons

chromium electronic configuration

1s2 2s2 2p6 3s2 3p6 3d5 4s1

copper electronic configuration

1s2 2s2 2p6 3s2 3p6 4s1 3d10

definition of ionisation energy

the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state

is ionisation endothermic?

ionisation requires energy so they are always an endothermic reaction processes and have a positive value

shielding

the more electron shells between the positive nucleus and negative electron that is being removed the less energy is required. there is a weaker attraction

atomic size

the bigger the atom the further away the outer electrons are from the nucleus. the attractive force between nucleus and outer electrons reduces - easier to remove electrons

nuclear charge

the more protons in the nucleus the bigger the attraction between nucleus and outer electrons. this means more energy required to remove the electron

definition of successive ionisation

the removal of more than 1 electron from the same atom

1st ionisation trends - groups

• ionisation energy decreases as we go down a group

• the atomic radius increases as we go down the group. outer electrons further from the nucleus. attractive force is weaker. energy required to remove an electron decreases.

• shielding increases as we go down the group. more shells between nucleus and outer shell. attractive force is weaker. energy required to remove an electron decreases

1st ionisation trends - periods

• as we go across the period there is an increasing no. of protons in the nucleus. this increases the nuclear attraction

• shielding is similar and distance from nucleus marginally decreases

• more energy required to remove an outer electron. ionisation energy increases

exceptions in 1st ionisation energy - periods

1. magnesium outer electrons fill 3s subshell. aluminium outer electrons fill 3p subshell. 3p subshell electrons are higher in energy which make it further from the nucleus so aluminium loses electrons easily

2. sulfur outer electron pair with another electron in same 3p subshell. when 2nd electron added to an orbital slight repulsion between two negatively charged electrons making 2nd electrons easier to remove