Trends in the Periodic Table

Question 1

Boiling temperature ………………..across a period

explain

Answer 1

• increases from group 1 to 4, then decreases from group 5 to 8
• boiling temp. increases across the three metals because of increasing strength in metallic bonding. this is because of the increasing number of electrons which form the ‘sea of delocalised electrons’. the charge on the metal ion also increases so the electrons are more closely attracted to the cations
• silicon’s boiling temp. is so high because of its giant covalent structure
• the other simple molecular structure have only weak van der Waals forces of attrcation between them, so have lower boiling temps.

Question 2

melting temperature ………………..across a period

explain

Question 3

the trend for atomic radius across a period is

explain

Answer 3

• a decrease
• though each member has an extra electron, the increasing nuclear charge counters this effect more and attracts the outer electrons even more, meaning the atomic radius decreases across a period, with exception of the noble gas, which is measured using the Van der Waals radius, so is not comparable to the metallic and covalent radii used for the metals and covalent radii used for the non-metals

Question 4

the trend in electronegativity across a period is

explain

Answer 4

• an increase in electronegativity from group 1 to 7
• this is because of the atomic radii decreasing, with the increase in nuclear charge increasing the atom’s ability to attract a pair of bonding electrons

Question 5

the trend in atomic radius down a groups is

explain

Answer 5

• increase

- each member has an extra shell of electrons, so the atomic radius increases

Question 6

the trend in thermal stability of compounds down a group is

explain

Answer 6

• an increase
• this is because the metallic radius increases, meaning the polarising effect of the ions decreases down the group. the decreasing charge density means the bonds in the compound are less distorted, so the bonds are not weakened in the same way as with the smaller ions higher up the group

Question 7

the trend in electrical conductivity………from groups 1 to 3

Answer 7

• increases

- this is because the number of electrons which make up the sea of delocalised electrons increases

Question 8

the trend in ionisation energies across a period is

explain

Answer 8

• increase, with slight variations, with dips at groups 3 and 6
• the general trend is because of the decreasing atomic radius and increasing nuclear charge across a period, but the number of shielding electrons staying the same, meaning the highest energy electrons is closer to the nucleus for each member, so is of lower energy than the previous member

Question 9

the trend in ionisation energies down a groups is

explain

Answer 9

• decrease
• the increase in nuclear charge is offset by the increase in shielding from the inner electrons against the outer electrons. the extra shell means the outer electrons have a higher energy, so the ionisation energy is reduced

Question 10

the trend in the size of atoms, anions and cations in terms of relative sizes are:

Answer 10

• positive ion is always smaller than the atom

- negative ion is always larger than the atom

Question 11

the trend in melting and boiling points down group 1 and 2 is
expain

Answer 11

• a decrease
• this is because the atomic radii increases down the group, so the free (delocalised) electrons experience a lower attraction tot he nucleus, so the bonding in the giant metallic lattice is weaker
• magnesium has an anomalously low melting and boiling point due to its lattice structure being different to that of other group 2 members

Question 12

the trend in melting and boiling points down group 7 is

explain

Answer 12

• an increase
• this is because these elements form diatomic molecules, so have van der Waals forces of attraction between the molecules (London forces), and the boiling points increase down the group because each new member have more electrons available to create a more contrasting dipole, so greater dipoles are created down the group and the force of attraction between molecules increases, increasing the amount of energy required to change state.

Question 13

the trend in reactivity with water down group 2 is
we can observe this by
explain

Answer 13

• increasing reactivity down the group
• increasing effervescence down the group, with calcium reacting vigorously
• the ionisation energy decreases down the group, so the required activation energy for the reaction to take place also decreases
• berylliium does not react with water because losing two electrons would make it small and have a high charge density, making it unstable, so does not react with water

Question 14

the solubility of the group 2 hydroxides………….down the group

Answer 14

-increases in solubility, magnesium hydroxide being insoluble, calcium hydroxide sparingly soluble and barium hydroxide soluble

Question 15

the solubility of the group 2 sulfates ……….down the group

Answer 15

• decreases

- barium sulfate’s low solubility is used in testing for sulfate ions in solution

Question 16

the reactivity of group 2 metals…………….down the group when reacting with dilute acids
the solubility of the salts produced………….down the group

Answer 16

• increase
• the lower ionisation energy down the group
• decrease in solubility of the salt produced

Question 17

the trend in electronegativity down group 7 is

explain

Answer 17

• decrease
• this is because the atomic radii increase down the group, the bonding pair is further and further away from the pull of the nucleus, so the ability to attract a pair of bonding electrons decreases

Question 18

the trend in first ionisation energy (electron affinity) down group 7 is
explain

Answer 18

• decrease, but fluorine being lower than chlorine
• this is because the atomic radii increases down the group, so the nucleus exerts a weaker force of attraction on the outer most electron.
• fluorine is the odd one out as its very small radius means it has a high electron density, sot he pull of the nucleus is slightly offset by the repulsion between the closely packed electrons. this means its first ionisation energy is lower than chlorine’s

Question 19

the trend in reactivity down Group 7 is

explain

Answer 19

• decrease
• same as for decreasing electronegativity down the group. the increasing atomic radii down the group means the atom is less able to attract a pair of bonding electrons, so therefore is less reactive

Question 20

the trend for the oxidising power of halogen atoms down the group is

Answer 20

• decrease down the group
• therefore chlorine can oxidise bromine and iodine, but iodine cannot oxidise bromine nor chlorine
• the halogens form halide ions in solution attached to water molecules,

Question 21

• the trend for the reducing power of halide ions down the group is:
• the experiment to observe this is:
• explanation is:

Answer 21

• increase down the group
• experiment with concentrated sulfuric acid acting as an acid and as an oxidising agent
• the fluoride or chloride ions are not strong enough reducing agents to reduce sulfuric acid, so a hydrogen halide forms when the sulfuric acid produced ah H+ ion to form a hydrogen halide
• for bromide and iodide ions, this is different, with their stronger reducing power meaning they form a halogen gas