Inorganic 1: Periodicity

Question 1

Label the different blocks of the periodic table.

Answer 1

Question 2

Why are scandium and zinc not transition metals?

Answer 2

Because they don’t form any compounds in which they have partly filled d-orbitals

Question 3

What are lanthanides?

Answer 3

Metals which are not often encountered
Tend to form +3 ions in their compounds

Question 4

What are actinides?

Answer 4

Radioactive metals
Only thorium and uranium occur naturally in the Earth’s crust in high quantities

Question 5

What block does helium fall into?

Answer 5

The s block
But is placed over the noble gases

Question 6

What is periodicity?

Answer 6

The patterns in properties of elements on the periodic table

Question 7

Describe the structures of sodium magnesium, and aluminium.

Answer 7

Forms giant metallic lattices
Positive metal ions in sea of delocalised electrons
Which form strong electrostatic forces of attraction

Question 8

Describe the structure of silicon.

Answer 8

Semi-metal
Macromolecular (giant covalent lattice)
Very high melting point due to many strong covalent bonds

Question 9

Describe the structures of phosphorus, sulfur, and chlorine.

Answer 9

Simple molecular non-metals
P4, S8, Cl2
Lower melting points than
Van der Waals intermolecular forces
S8 has highest melting point as it has the most electrons so strongest van der Waals

Question 10

Describe the structure of argon.

Answer 10

Noble gas
Monatomic
Low melting point

Question 11

Describe the trend in melting and boiling points of period 3 elements.

Answer 11

1) Melting point increases from sodium to aluminium
2) Charge on the positive ions increases, and more delocalised electrons are released
3) So electrostatic attraction between delocalised electrons and metal ion increases
4) So melting point increases

Question 12

Why is the melting point of silicon so high?

Answer 12

1) Silicon is a giant covalent lattice
2) So atoms are joined by many strong covalent bonds
3) Which require a large amount of energy to break

Question 13

Why are the melting points of phosphorous, sulfur and chlorine much lower than the other period 3 elements?

Answer 13

1) Because they are simple molecules, P4, S8, and Cl2
2) Melting point depends on the size of the van der Waal forces between molecules
3) Sulfur has the highest melting point because it has the most electrons, so strongest van der Waals

Question 14

Why does argon have a low melting point?

Answer 14

1) It is monatomic
2) Only has weak van der Waal forces
3) Which requires a smaller amount of energy to overcome

Question 15

Draw a graph to show the trend in melting points for period 3 elements.

Answer 15

Question 16

Describe the trend in atomic radius across a period.

Answer 16

1) Atomic radius decreases across a period
2) Nuclear charge increases as number of protons increases
3) Shielding remains the same, so force of attraction between nucleus and outer electron increases

Question 17

Describe the trend in atomic radius down a group.

Answer 17

1) Atomic radius increases down a group
2) Shielding increases as number of shells increases
3) So there is a weaker force of attraction between the nucleus and outer electrons

Question 18

Describe trend in first ionisation energy across a period.

Answer 18

1) Generally, there is an increase in first ionisation energy as nuclear charge increases as number of protons increases, and shielding remains the same
2) So there is a stronger force of attraction between the nucleus and outer electron
3) So it requires more energy to remove it
4) There is a decrease at group 3 because the outer electron is in a p orbital, whereas in group 2 it is in an s orbital
5) The p orbital is a higher energy level, so it takes less energy to remove
6) There is a decrease at group 6 because the outermost electron is paired in an orbital, whereas in group 5 it only singly occupies the orbital
7) Electron pair repulsion means that the outermost electron is repelled further so is easier to remove

Question 19

Why does first ionisation energy decrease down a group?

Answer 19

1) Shielding increases as number of shells increases
2) So there is a weaker force of attraction between the nucleus and the outermost electron
3) So it requires less energy to remove

Question 20

Define first ionisation energy.

Answer 20

The energy required to remove one mole of electrons from one mole of atoms in their gaseous state to produce one mole of 1+ ions
X(g) –> X+(g) + e-

Question 21

Define second ionisation energy.

Answer 21

The energy required to remove one mole of electrons from one mole of 1+ ions in their gaseous state to produce one mole of 2+ ions
X+(g) –> X2+(g) + e-

Question 22

Describe trend in successive ionisation energy.

Answer 22

1) Successive ionisation energy increases
2) As more electrons are removed, there is less shielding, so the force of attraction between the nucleus and the outermost electron increases
3) There is a sharp increase when the first electron is removed from a lower shell
4) Because the amount of shielding significantly decreases, and force of attraction between nucleus and outer electron gets stronger

Question 23

Define successive ionisation energy.

Answer 23

The energy required to remove each subsequent electron from an ion after one or more electrons have already been removed