The Periodic Table (incl. Group 2 and Group 17)

Question 1

What is a group

Answer 1

Vertical column of elements in the Periodic Table, where elements within the same group have the same outer electron configuration and hence similar chemical properties

Question 2

What is a period

Answer 2

A horizontal row of elements in the Periodic Table, where elements within the same period have the same number of electron shells.

Question 3

What is screening effect

Answer 3

The partial decrease in electrostatic attraction between the nucleus and its valence electrons due to repulsive forces from other electrons present

Question 4

What is nuclear charge

Answer 4

Electrostatic attraction between the protons in the nucleus of an atom and the surrounding electrons.

Question 5

What is screening effect?

Answer 5

The partial decrease in electrostatic attraction between the nucleus and its valence electrons due to repulsive forces from other electrons present.

Question 6

What is electronegativity?

Answer 6

Ability of an atom in a molecule to attract bonding electrons in a covalent bond towards itself.

Question 7

What are the exceptions in increase in first ionisation energy across the period, and why?

Answer 7

Mg and Al
3s2 vs 3s2 3p1
Smaller amount of energy is required to remove the 3p electron in Al, although it is of higher energy than the 3s electron of Mg

P and S
3p3 vs 3p4
Interelectronic repulsion between the paired 3p electrons in S
Smaller amount of energy required to remove the paired 3p electron in S than the unpaired 3p electron in P.

Question 8

How does melting point change across a period?

Answer 8

Melting point of elements generally increases across a period (across the giant metallic substances) until a maximum is reached at Group 14 (giant molecular substances, metalloids) and then decreases across the period (simple molecular substances)

Question 9

Why does melting point of metals increase across period?

Answer 9

1. The number of delocalized valence electrons increases across the period
2. The cationic charge of ions increases
3. Cationic radius decreases down period

Question 10

Why does the melting point of simple molecular substances increase across period?

Answer 10

Strength of id-id interactions increases with increasing size of electron cloud (Ar < Cl2 < P4 < S8)

Question 11

How does electrical conductivity change across a period?

Answer 11

Electrical conductivity generally increases through the metals, then decreases through the metalloids and non-metals

Question 12

How to find the highest O.N. of an element

Answer 12

By the maximum number of valence electrons gained, lost or shared to achieve an electronic configuration of ns2 np6.

Question 13

How does the maximum O.S. vary across a period?

Answer 13

The maximum O.S. increases across a period until a maximum is reached

Question 14

How does ionic and covalent character of oxides and chlorides change across a period, and why?

Answer 14

As electronegativity difference between O/Cl and the element decreases across the period, ionic character decreases, and covalent character increases.

Question 15

Why is AlCl3 (simple molecular with ionic character) predominantly covalent compared to Al2O3?

Answer 15

The high charge density of Al3+ polarises the large electron cloud of the Cl- ion, hence making AlCl3 covalent. Also because of the smaller E.N. difference.

Question 16

Why does the thermal stability of Group 2 carbonates increase down the group?

Answer 16

1) The larger the size of the anion, the easier it is to be distorted and more polarisable. (Size of CO32- remains constant)
2) The charge density of cation (polarisability) Depends on charge and ionic radius. If it has high polarising power, the distortion weakens the C–O bonds within the carbonate ion, making it less stable.

Question 17

Why does oxidising power off Group 17 Elements (halogens) decrease down the group?

Answer 17

Ability to attract bonding electrons, and hence electronegativity, decreases down the group. Thus oxidising power of halogens decreases down the group.
*Can also refer to Standard Electrode Potential

Question 18

When halogens that are higher in group 17 oxidise aqueous halide ions that are lower in the group what reaction is it also called?

Answer 18

Displacement reaction

Question 19

How does the stability of Group 17 hydrides change down the group, and why?

Answer 19

It decreases, because bond energy decreases, and thus covalent bond strength decreases, causing thermal stability to decrease.

Question 20

Why are chromium and copper exceptions in the filling up of subshells with electrons?

Answer 20

For chromium, the half-filled d subshell is found to be more stable than 3d4 4s2 config.

For copper, the fully-filled d subshell is found to be more stable than the 3d9 4s2 config.