3.1.1 Atomic Structure

Question 1

Where are protons and neutrons found?

Answer 1

Protons and neutrons are found in the centre of the atom called the nucleus.

Question 2

What can protons and neutrons also be called?

Answer 2

Nucleons

Question 3

Where are electrons found?

Answer 3

Electrons surround the nucleus in shells/energy levels.

Question 4

What are the relative mass and relative charge of a proton?

Answer 4

Relative mass= 1
Relative charge= +1

Question 5

What are the relative mass and relative charge of a neutron?

Answer 5

Relative mass= 1
Relative charge= 0

Question 6

What are the relative mass and relative charge of an electron?

Answer 6

Relative mass= 1/1840
Relative charge= -1

Question 7

Define atomic number.

Answer 7

The number of protons in the nucleus.
Same amount of protons and electrons.

Question 8

Define mass number.

Answer 8

Sum of the number of protons and neutrons combined.

Question 9

What are cations?

Answer 9

Positive ions.
An atom that has lost electrons so there is more protons than electrons.
p>e-

Question 10

What are anions?

Answer 10

Negative ions.
An atom that has gained electrons so there is more electrons than protons.
p<e-

Question 11

Define isotope.

Answer 11

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons.

Question 12

Are the properties of isotopes of the same element the same or different?

Answer 12

Isotopes of the same element have the same chemical properties because they have the same electron configuration.

Question 13

What are the key differences between Thompson’s and Bohr’s models?

Answer 13

• The electrons are kept in the electron shells.
• There is a small positive nucleus with protons and neutrons.

Question 14

Define ionisation energy and give an example equation using the first ionisation energy of potassium (K)

Answer 14

Ionisation energy is the amount of energy needed to remove a mole of electrons from a mole of atoms in the gaseous state.
e.g. K(g) —> K+(g) + e-

Question 15

What are the three factors that will influence ionisation energy?

Answer 15

1. Nuclear charge (number of protons in the nucleus)
   Higher nuclear charge= stronger force of attraction between electron and nucleus= higher IE
2. Distance from nucleus
   If e- is closer to the nucelus= stronger force of attraction= higher IE
3. Shielding
   Less shielding= stronger force of attraction= higher IE

Question 16

Why is the second ionisation energy of B higher than the first?

Answer 16

The second electron is removed from an ion that already has a positive charge.

Question 17

EXAM QUESTION:
The following data shows the first seven successive IE energies of a period 3 element. State which element it is and explain your reasoning.

1st e- removed = 786.5 kJmol-1
2nd e- removed= 1577.1 kJmol-1
3rd e- removed= 3231.6 kJmol-1
4th e- removed= 4355.5 kJmol-1
5th e- removed= 16091.1 kJmol-1
6th e- removed= 19805.6 kJmol-1
7th e- removed= 23780.4 kJmol-1

Answer 17

Silicon
- The largest increase is between the 4th and 5th ionisation energies.
- The 5th electron is on the shell closest to the nucleus.
- The element must have 4 electrons in its outer shell.

Question 18

Why is Li a bigger atom than Be?

Answer 18

• Lithium has fewer protons so it can’t pull its electrons as closely.
• Both atoms have the same number of shells.
• They have the same shielding.
• Be has more protons.
• So it attracts the outermost electrons more strongly.

Question 19

Why is Li a bigger atom than He?

Answer 19

• Lithium has an extra electron shell and is further away from the nucleus.
• The outer electron is more shielded.
• The outer electron is less strongly attracted to the nucleus.

Question 20

Why is Li a bigger atom than F?

Answer 20

• F has more protons, so there is a stronger attraction.
• Both have the same number of shells.
• Same shielding,
• F has more protons so it attracts the outermost electrons more strongly.

Question 21

Why is Li+ a smaller ion than F-?

Answer 21

• Li+ atom only has one shell.
• Its electrons are closer to the nucleus and there is no shielding.
• So outer electrons are more strongly attracted.

Question 22

Define an orbital.

Answer 22

A region within an atom that can hold up to two electrons with opposite spins.

Question 23

Exceptions for electron configuration.

Answer 23

• Chromium = 1s2 2s2 2p6 3s2 3p6 4s1 3d5
• Copper= 1s2 2s2 2p6 3s2 3p6 4s1 3d10
• D block ions= First in, first out. Remove electrons from 4s subshell before 3d subshell.

Question 24

Explain the trend in 1st IE across period 2 elements.

Answer 24

1. General increase in IE across period 2.
2. Across period 2 there is a greater nuclear charge.
3. More protons, same shielding
4. So there is a greater attraction between the nucleus and outer shell.
5. The first e- from Be is removed from a 2s subshell. The first e- from B is removed from a 2p subshell. 2p subshell is higher in energy than 2s subshell therefore less energy is needed to remove an e- from B.
6. The first e- removed from N is from a 2p subshell and is unpaired. The first e- removed from O is from a 2p subshell but is from a paired orbital. O has a lower IE due to electron pair repulsion, therefore less energy is needed to remove electrons from O.

Question 25

How does IE change down a group?

Answer 25

1. Atoms get bigger, with more shells. 2. More shielding. 3. Weaker attraction from the nucleus to electrons in the outer shell. 4. IE decreases down the group.

Question 26

State and explain the trend in atomic radius down a group.

Answer 26

Down the group atomic radius increases because there are more shells so more shielding. So there is less attraction to the outermost electrons.

Question 27

Why does the atomic radius get smaller from right to left across a period?

Answer 27

The nuclear charge (proton number) increases. Greater attraction between electrons and nucleus. Same shielding.

Question 28

Stages of a TOF mass spectrometer.

Answer 28

1. Ionisation 2. Acceleration 3. Ion drift/Deflection 4. Detection

Question 29

What are the two methods of ionisation?

Answer 29

1. Electron impact 2. Electrospray ionisation

Question 30

Explain the method of electron impact ionisation.

Answer 30

1. Sample is vapourised. 2. High energy electrons from an electron gun are fired at it. 3. An electron is knocked off each particle, forming a positive ion. X(g) ---> X+(g) + e-

Question 31

Explain the method of electrospray ionisation.

Answer 31

1. Sample is dissolved in a volatile solvent. 2. Sample is injected through a fine hypodermic needle attached to the positive terminal of a high voltage power supply. 3. A proton is gained on each particle, forming a positive ion.

Question 32

Why are the sample particles ionised?

Answer 32

So they can be accelerated towards the negatively charged plate. So they generate a current when they gain an electron as they hit the detector.

Question 33

How are ions detected?

Answer 33

Each ion hits the detector. Ion gains an electron. Generates a current. Size of current is proportional to the abundance of the ion.

Question 34

Ar and KE formula

Answer 34

Ar= (mass 1 x abundance 1) + (mass 2 x abundance 2)/total abundance KE= 1/2 mv^2 v= d/t