Exam questions - electron config + ionisation

Question 1

State and explain the trend in the first ionisation energies of the elements in Group
2 from magnesium to barium.

Answer 1

decrease in ionisation energy because the ions get bigger
so there is weaker attraction of the lost electron to ion

Question 2

State the element in Period 3 that has the highest melting point.
Explain your answer

Answer 2

silicon
because it contains covalent bonding which is very strong and requires a lot of energy to break

Question 3

State the element in Period 3 that has the highest first ionisation energy.
Explain your answer.

Answer 3

Argon
has the largest nuclear charge and the same shielding/ number of shells

Question 4

Explain why nickel is ductile (can be stretched into wires).

Answer 4

layers of atoms can slide over eachother

Question 5

Explain why 4s subshell is filled prior to 3d but on ionization 4s electron are removed first?

Answer 5

filling of the orbitals is dependent on orbital energy while removal of electrons is dependent on orbital location

4s has a lower energy than 3d. So it gets filled up first. But 4s is farther away from the nucleus than 3d. So while removal of electrons, they are first removed from 4s. It is easier to remove electrons that are farther away from the nucleus.

Question 6

What is relative atomic mass ?

Answer 6

average mass of an atom of an element based on 1/12 mass of a C12 atom

Question 7

In a TOF mass spectrometer, each 84Kr+
ion is accelerated to a kinetic
energy of 4.83 × 10−16 J and the time of flight is 1.72 × 10−5 s

Calculate the length, in metres, of the TOF flight tube.
The Avogadro constant, L = 6.022 × 1023 mol−1

Answer 7

KE = 1/2mv^2

v^2 = KE/ 0.5m

mass of ion: 84/1000 div by 6.02 x 10^23 = 1.395 x 10^-25

div by 1000 because mass has to be in kilograms and div by AV const because the mass number 84 is the number of grams per mol, and you are trying to find mass in kg of one ion.

v^2 = 6924731
v = 83214
d = v x t
d = 83214 x 1.72 x 10 -5
d = 1.43 m

Question 8

Give two reasons why it is necessary to ionise the isotopes of chromium
before they can be analysed in a TOF mass spectrometer.

Answer 8

• ions can be accelerated by an electric field ( have to be charged particles to interact with electric field)
• ions create a current when hitting a detector

Question 9

Describe how the molecules are ionised using electrospray ionisation.

Answer 9

• molecules are dissolved in a volatile solvent
• injected into a needle which has a high voltage
• each molecule gains a proton

Question 10

Explain the pattern in the first ionisation energies of the elements from lithium to
neon.

Answer 10

1a. 1st IE increases
1b. More protons/increased nuclear charge
1c. Electrons in same energy level / shell
1d. No extra/similar shielding

2a. B lower than Be
2b. Outer electron in (2)p
2c. higher in energy than (2)sv

3a. O lower than N
3b. 2 electrons in (2)p need to pair
3c. pairing causes repulsion

Question 11

Why do isotopes have no difference in chemical properties ?

Answer 11

Same number of outer eleectrons