Atomic Structure

Question 1

Relative sub-atomic particle values

Answer 1

Relative mass - proton = 1, neutron = 1, electron = 1/1840
Relative charge - proton = +1, neutron = 0, electron = -1.

Question 2

Structure of an atom

Answer 2

Most mass is concentrated in the centre where the nucleus is (small area compared to the whole atom).

Question 3

Protons

Answer 3

Protons are fixed in an element and identify which one it is.

Question 4

Neutrons

Answer 4

They change in each atom of an element to create isotopes.

Question 5

Electrons

Answer 5

They orbit the nucleus in electron shells.
Same number of protons and electrons (in a neutral atom).

Question 6

Isotope abundance equation

Answer 6

(isotope mass 1 x isotope abundance 1) + (isotope mass 2 x isotope abundance 2) /
total abundance

Question 7

Mass Spectrometry -
Electron Impact

Answer 7

The sample is vaporized and then an electron gun (a hot wire filament with a current that emits electrons) fires electrons at it. The high energy electrons knock off one electron when they collide with the particles. This forms +1 ions.

Question 8

Electron Impact equation

Answer 8

X(g) + e- —-> X+(g) + 2e-

Question 9

Mass Spectrometry -
Electrospray Ionisation

Answer 9

The sample is dissolved in a volatile (evaporates quickly) solvent (water or methane) and injected through a fine needle to create a fine mist. The tip of the needle is attached to the positive terminal of a high voltage power supply. The particles are ionised and gain a proton from the solvent as they leave the needle.

Question 10

Electrospray Ionisation equation

Answer 10

X(g) + H+ —–> XH+(g)

Question 11

Mass Spectrometry -
Acceleration

Answer 11

The positive ions are accelerated using an electric field so that they all have the same kinetic energy. Since all the particles have the same kinetic energy, the velocity depends on the mass of each particle. Lighter particles have a faster velocity, heavier particles have a slower velocity.

Question 14

Mass Spectrometry -
Ion Drift

Answer 14

The ions move through a region with no electric field. They drift through with the same speed as the acceleration so they will drift at different speeds according to their masses. The lighter ions travel faster and reach the detector quicker than the heavier ions.

Question 15

Mass Spectrometry -
Ion Detection

Answer 15

The positive ions hit the negatively charged plate and are discharged by gaining electrons from the plate. This generates a movement of electrons and a current is measured. The size of the current gives a measure of the number of ions hitting the plate.

Question 16

Mass Spectra

Answer 16

When using electron impact, some peaks may be lower m/z values due to fragments caused by the break up of molecular ions.

Question 17

First Ionisation Energy

Answer 17

The energy required to remove one electron from each atom of one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 18

Successive Ionisation Energies

Answer 18

A measure of the energy required to remove each electron in turn.
Li(g) –> Li+(g) + e- (first)
Li+(g) –> Li2+(g) + e- (second)
Li2+(g) –> Li3+(g) + e- (third)

Question 19

Jumps in ionisation energies

Answer 19

The big jumps occur when the shells become empty and the jump to start emptying the next one.

Question 20

Ionisation Energy

Answer 20

As each electron is removed there is less repulsion between the remaining electrons so they are drawn closer to the nucleus.
As the distance decreases to the nucleus, the electrons are held more strongly so more energy is required to remove them.

Question 21

Factors impacting ionisation energies

Answer 21

Atomic Radius
Shielding
Nuclear Charge

Question 22

Ionisation energy down the group

Answer 22

Atoms get bigger, shielding increases, therefore the attraction between the nucleus and the outer electron is weaker.

Question 23

Ionisation energy across the period

Answer 23

Increased nuclear charge (more protons), so atoms get smaller, therefore a stronger attraction between the nucleus and the outer electron.

Question 24

How do electrons fill orbitals?

Answer 24

The 2 electrons per subshell have tot have opposite spins (one clockwise and one anticlockwise).

Question 25

Kinetic energy equation

Answer 25

KE = 1/2mv^2
v = d/t
Therefore, t = d square root m/2KE

Question 26

What is a photon?

Answer 26

If an electron is in an excited state, it can return to a lower energy level and it loses energy. The amount of energy lost will be equal to the difference in the energy levels it moves between. The energy is released as a photon.

Question 27

The filling order of electrons

Answer 27

Orbitals are not filled in numerical order because the principal energy levels get closer together as you get further from the nucleus.

Question 28

Anomalies to the filling order

Answer 28

Cu - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10.
Cr - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5.