Atomic Structure

Question 1

How much of chlorine is Cl-35?

Answer 1

75%. The rest is Cl-37

Question 2

Define Ar

Answer 2

The mean mass of an atom of an element divided by one twelfth of the mass of a Carbon-12 atom.

Question 3

Define Mr

Answer 3

The average mass of the molecule divided by a twelfth of the mass of a Carbon-12 atom.

Question 4

How does a mass spectrometer work?

Answer 4

The compound (gas) is ionised and is accelerated to a constant kinetic energy to the detector by the electric field (positive ions attracted to negative plate). The drift stage is where is goes through a hole in the plate to the flight tube (vacuum so no collisions). The detector is negative so attracts the ions. The lightest ions will reach it first and so are detected first. They gain an electron so a current flows. The abundance is calculated by the size of the current flowing. The data is recorded on a mass spectrum.

Question 5

How much of bromine is Br-79?

Answer 5

50%. The rest is Br-81.

Question 6

How does ‘electron impact’ work in mass spectrometry?

Answer 6

An electron gun fires high energy electrons at the compound which knocks off one electron off each particle making them positive. This can create fragments where the compound splits, the compound must be a gas.

Question 7

How does ‘electrospray’ work in mass spectrometry?

Answer 7

The sample is dissolved in a volatile solvent and forced through a fine needle at high pressure which is connected to the positive terminal of a high voltage supply producing tiny positive droplets where each particle has gained a proton. This is injected into the spectrometer. The solvent evaporates in the vacuum. No fragments are created.

Question 8

Describe the arrangement of electrons in atoms

Answer 8

They are arranged in energy levels (shells). These have sub-levels (sub-shells). Each energy level/sub-level is made up of electron orbitals which can each hold two electrons.

Question 9

The s sub-level

Answer 9

1 orbital so maximum of 2 electrons.

Question 10

The p sub-level

Answer 10

3 orbitals so maximum of 6 electrons

Question 11

The d sub-level

Answer 11

5 orbitals so maximum of 10 electrons

Question 12

How do electrons fill orbitals

Answer 12

They fill up from the lowest energy level/sub-level upwards. Atomic orbitals of the same energy fill up singly before pairing starts as electrons repel each other. No orbital can hold more than two electrons.

Question 13

The order of sub levels

Answer 13

1s2s2p3s3p4s3d4p

Question 14

1st ionisation energy

Answer 14

Energy required to remove one electron from each atom in a mole of gaseous atoms producing a mole of 1+ gaseous atoms.

Question 15

What happens to the 1st ionisation energy as you go down a group of metals?

Answer 15

It decreases because the radius is larger and there is more shielding so the attraction from the nucleus to the outer electron shell is less so electrons are easier to lose.

Question 16

What is the general trend with the 1st ionisation energy as you go across (right) a period?

Answer 16

It increases because there are more protons so there is a stronger attraction between the nucleus and outer shell so the atoms are smaller (the nucleus attracts the shells inwards) and electrons are less easy to lose.

Question 17

The dip at group 3 for IE

Answer 17

Group 3 elements lose their first electron from a p orbital which has a higher energy than an s orbital (which group 2 elements lose the first electron from) so needs less energy to remove it.

Question 18

The dip at group 6 for IE

Answer 18

Group 6 elements lose the first electron from an orbital with 2 electrons in so there is electron to electron repulsion making it easier to lose one of them.

Question 19

Cr electron configuration

Answer 19

[Ar] 4s1 3d5

Question 20

Cu electron configuration

Answer 20

[Ar] 4s1 3d10

Question 21

Define isotope

Answer 21

Atoms with the same number of protons but different numbers of neutrons.

Question 22

How does the pattern for first ionisation energy of group 2 elements give evidence for the electron configuration in shells?

Answer 22

It decreases as you go down the group even though the nuclear charge increases. This suggests the outer electron is in a main level that gets further from the nucleus in each case and the inner electron shells shield the nuclear charge.

Question 23

How does the pattern for first ionisation energy of period 3 elements give evidence for the electron configuration in sub-shells?

Answer 23

There are dips at group 3 and 6 which goes against the expected trend of it increasing from left to right due to an increase in nuclear charge. They give evidence for s and p sub-shells respectively.

Question 24

How does the pattern for successive ionisation energies of group 3 elements give evidence for the electron configuration in shells?

Answer 24

There are some sharp increases in ionisation energy at specific ones. This suggests that the electrons lost before this ionisation with the sharp increase were in an energy level further from the nucleus than the one after the ionisation. You can use the jumps in successive ionisation energies to see how many electrons are in each energy level.