3.1 The periodic table

Question 1

What is periodicity?

Answer 1

Periodicity is the trend in properties that is repeated across each period.

Question 2

What do elements in the same group have in common?

Answer 2

They have:
- the same number of outer shell e-
- the same type of orbitals
- similar properties

Question 3

How is abbreviating the electron configuration of some elements useful?

Answer 3

It allows us to clearly see which sub-shell the outer e- are in and where the element can be found in the periodic table.

Question 4

What is the electron configuration of Na?

Answer 4

1s2. 2s2. 2p6. 3s1.
or [Ne]3s1

Question 5

What is first ionisation energy?

Answer 5

The first ionisation energy of an element is the energy required to remove 1 electron from each atom in 1 mole of the gaseous element to form 1 mole of gaseous 1+ ions.

Question 6

What is the equation for the first I.E. of Na?

Answer 6

Na(g) -> Na+(g) + e-

Question 7

What is I.E. measured in?

Answer 7

kJmol-1

Question 8

What are the factors that affect I.E.?

Answer 8

1. atomic radius - larger atomic radius = smaller nuclear attraction = smaller I.E.
2. nuclear charge - higher nuclear charge = greater nuclear attraction = greater I.E.
3. electron shielding - inner shells of e- repel outer e- (all -) - more inner shells = greater shielding effect = smaller nuclear attraction = smaller I.E.

Question 9

What is successive ionisation energy?

Answer 9

Successive ionisation energy is the energy required to remove each e- in turn from an ion in 1 mole of gaseous ions (ion x+) to form 1 mole of gaseous ions (ion (x+1)+)

Question 10

Explain why each successive I.E. is greater than the one before

Answer 10

• As each e- is removed, there is less repulsion between remaining e- and each shell will be drawn in closer to the nucleus
• due to the positive charge of the nucleus beginning to outweigh the negative charge of the e-.
• As the distance between the nucleus and each e- decreases, the nuclear attraction increases, so more energy is needed to remove each successive e-.

Question 11

How does successive I.E. support the Bohr model?

Answer 11

Successive I.E.’s provide evidence for shells as once all the e- from the outer shell have been removed, e- from the next shell begin to be removed. This requires a larger amount of energy as there is a smaller distance and less electron shielding, so there is a stronger attraction between the nucleus and outer e-, so we will see a bigger jump in I.E. indicating a different shell closer to the nucleus.

Question 12

Why is the I.E. of each noble gas the highest in the period?

Answer 12

These atoms have a full outer shell of electrons and a high positive attraction from the nucleus so more energy is needed to remove an electron.

Question 13

Explain the trend in I.E. going across a period

Answer 13

• nuclear charge (no. of protons in nucleus) increases, so there is a higher nuclear attraction on the outer e-
• atomic radii decreases as increased nuclear charge pulls e- inwards, decreasing the distance between the nucleus and outer e-, causing there to be a higher nuclear attraction on the outer e-
• same no. of inner shells, so electron shielding stays the same
• as the attraction between the nucleus and outer e- increases, more energy needed to remove an e-
• I.E. increases across a period

Question 14

Why is there a decrease in I.E. between Mg (gr 2) and Al (gr 13)?

Answer 14

• gr 13 elements have their outer e- in a p-orbital whereas gr 2 elements have theirs in an s-orbital
• p-orbitals have slightly higher energy than s-orbitals so the outer shell is further from the nucleus
• therefore the nuclear attraction on the outer e- is slightly weaker so the I.E. is lower

Question 15

Why is there a decrease in I.E. between N (gr 15) and O (gr 16)

Answer 15

• both gr 15 and gr 16 elements have their outer e- in a p-orbital
• however, for gr 15 elements, each p-orbital only contains a single e-
• in gr 16, the outermost e- is spin paired with another e- in the orbital
• so the e- experience some repulsion, making the first outer e- slightly easier to remove so the I.E. is lower

Question 16

Explain the large decrease in 1st I.E. between the end of one period and the start of the next.

Answer 16

• at the start of another period, another shell has been added which is further from the nucleus
• this leads to an increase in the distance between the nucleus and the outer shell and an increase in electron shielding
• this causes the nuclear attraction on the outer e- to decrease
• so less energy is needed to remove an e-
• therefore the I.E. is much lower

Question 17

Explain the trend in I.E. going down a group

Answer 17

• no. of shells increases, atomic radii increases/distance between nucleus and outer shell increases, so weaker nuclear attraction on outer e-
• more inner shells, shielding effect increases, so weaker nuclear attraction
• no. of protons/nuclear charge increases however the resulting increased attraction is outweighed by the increases in distance and shielding
• as the attraction between the nucleus and outer e- decreases, less energy needed to remove an e-
• so I.E. decreases going down a group

Question 18

Describe the structure of a giant metallic lattice

Answer 18

• positively charged metal ions are held in fixed positions in regular arrangement
• the negatively charged outer e- are delocalised and are spread throughout the structure and are shared between all the atoms in the structure
• the delocalised e- are free to move
• over the whole structure, the charges must balance
• the metal is held together by the strong attractions between the positive metal ions and the negative delocalised e-

Question 19

Explain why metals have high melting and boiling points

Answer 19

• e- are free to move through the structure but the positive metal ions stay in fixed positions
• the electrostatic attraction between the negative delocalised e- and the positive metal ions is very strong
• a lot of energy is required to overcome the strong metallic bonds and dislodge the ions from their rigid positions in the lattice

Question 20

Explain why metals are good electrical conductors

Answer 20

• delocalised e- can move freely and carry charge through the structure

Question 21

Explain why metals are both ductile and malleable

Answer 21

• the delocalised e- are able to move so the layers of atoms are able to slide over each other easily

Question 22

How do elements change moving across periods 2 and 3?

Answer 22

• metals to non-metals
• solids to gases

Question 23

Why is Si harder to classify as a metal/non-metal?

Answer 23

It is shiny like metals, but is brittle.
It conducts electricity, but very poorly.

It is an ‘in-between’ element, usually classified as a semi-metal/metalloid.

Question 24

What happens to the melting points of elements between gr 1 and gr 14?

Answer 24

Between gr 1 and 14, melting points increase steadily because the elements have giant structures.

For each successive group, if an element has a giant metallic lattice, the nuclear charge increases across the period as well as the no. of outer e-, resulting in a stronger attraction.

If the element has a giant covalent lattice, each successive group has more e- which form covalent bonds.

Question 25

What happens to the melting points of elements between gr 14 and gr 15?

Answer 25

Between gr 14 and gr 15, there is a sharp decrease in melting point because the elements have simple molecular structures. Molecules are held together by weak intermolecular forces.

Question 26

What happens to the melting points of elements between gr 15 and gr 18?

Answer 26

Between gr 15 and gr 18, the melting points remain relatively low as the elements have simple molecular structures.

Question 27

Briefly describe the trend in boiling points across periods 2 and 3

Answer 27

Boiling point…
- increases steadily up to gr 14
- decreases sharply between gr 14 and 15
- slays low from gr 15-18

Question 28

Describe the structure and bonding of diamond

Answer 28

Diamond forms a giant covalent lattice where each carbon atom bonds to 4 other carbon atoms making it extremely strong,

Question 29

Describe the structure and bonding of graphene

Answer 29

Graphene forms a 2D giant covalent lattice, one carbon atom thick, of interlocking hexagonal carbon rings. It is extremely strong, light and can conduct electricity.