Atomic Structure

Question 1

Define Isotopes

Answer 1

Isotopes are atoms with the same number of protons, but different numbers of neutrons

Question 2

What are the chemical and physical properties like with isotopes?

Answer 2

Similar chemical but different physical properties

Question 3

What does m/z stand for?

Answer 3

Mass/charge

Question 4

Describe the four steps for how positive ions are formed during electron impact

Answer 4

1. A Vaporised sample is injected at low pressure
2. An electron gun fires high energy electrons at the sample
3. This Knocks out an outer electron
4. Forming positive ions with different charges, e.g. Ti(g) => Ti*(g) + e-

Question 5

Describe the five steps of electro-spray ionisation

Answer 5

1. The sample is dissolved in a volatile, polar solvent
2. It is then injected through a fine hypodermic needle giving a fine mist or aerosol.
3. The tip of needle has high voltage
4. At the tip of the needle the sample molecule, M, gains a proton, H+, from the solvent forming MH+
5. M(g) + H* => MH*(g)
6. The solvent evaporates away, while the MH* ions move towards the negative plate

Question 6

What is the kinetic energy like with particles in the TOF spectrometer?

Answer 6

The same

Question 7

What is the equation for measuring the kinetic energy in TOF spectrometry?

Answer 7

KE= ½ m v2

Question 8

Rearrange the kinetic energy equation to make velocity ‘v’ the subject of the formula

Answer 8

v = (square root of) 2KE / m

Question 9

Which type of particles move faster through the flight tube?

Answer 9

Smaller particles

Question 10

Write the combined equation for the kinetic energy of a particle travelling through a flight tube

Answer 10

t = distance x (square root of) m / 2KE

Question 11

Write the equation for working out the relative atomic mass

Answer 11

Sum(isotopic mass x relative abundance)/ total relative abundance

Question 12

Br has two isotopes 79 and 81. It forms 3 peaks: 158, 160 and 162. How was each of these 3 peaks formed?

Answer 12

158= 79 + 79    
160=  79 + 81  or 81+ 79   
162= 81 + 81

Question 13

Br has two isotopes- 79 and 81. Why is the abundance at 160 double that of 158 and 162?

Answer 13

13. Can either be 79 + 81 or 81+ 79

Question 14

The mass of a molecule is 521.1 for MH+. Electro spray ionisation was used. What is the Mr of the molecule?

Answer 14

520

Question 15

How many electrons does s,p,d and f sub energies hold?

Answer 15

2
6
10
14

Question 16

How many electrons does an orbital hold?

Answer 16

2

Question 17

Write the sub levels for an atom ending with 5p (i.e. 1s,2s etc). You don’t need to include the number of electrons

Answer 17

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p

Question 18

What is the rough outline of the periodic table. Label: S-block, d-block, p-block and f-block?

Answer 18

S on left, d in middle, p on right, f at the bottom

Question 19

Define first ionisation energy

Answer 19

The first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge

Question 20

Write the first ionisation energy of Hydrogen including state symbols

Answer 20

H(g) => H*(g) + e-

Question 21

Write the second ionisation energy of Titanium including state symbols

Answer 21

Ti(g) => T2(g) + e-

Question 22

What are the 3 factors affects ionisation energy?

Answer 22

Attraction of the nucleus
Distance of the electrons from the nucleus
Shielding

Question 23

There is a large jump in ionisation energies between 4 electrons removed and 5. What does this mean for the group number?

Answer 23

It must be Group 4

Question 24

In a spin box, how many arrows are there?

Answer 24

2 (one up and one down)

Question 25

Why has Helium the largest first ionisation energy?

Answer 25

It’s first electron is in the first shell closest to the nucleus and there are no shielding effects from inner shells.
He has a bigger first ionisation energy than H as it has one more proton.

Question 26

Why do first ionisation energies decrease down a group?

Answer 26

As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 27

Why is there a general increase in first ionisation energy across a period

Answer 27

As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater.

Question 28

Why has Na a much lower first ionisation energy than Neon?

Answer 28

This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. This means there will be a weaker nuclear attraction and So Na’s outer electron is easier to remove and has a lower ionisation energy.

Question 29

Why is there a small drop from Mg to Al?

Answer 29

Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p sub-shell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons.

Question 30

Why is there a small drop from P to S?

Answer 30

With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.