3.2 Periodic trends

Question 1

what are the 6 different physical periodic trends?

Answer 1

1. atomic radius
2. ionic radius
3. melting point
4. first ionisation energy
5. electronegativity
6. electron affinity

Question 2

explain the period trends in atomic radius across a period

Answer 2

decreases across a period because same shielding effect and higher nuclear charge pulls electrons inwawrds

Question 3

explain the periodic trend in atomic radius down a group

Answer 3

increases down a group because electrons are added in shells further from the nucleus with the same nuclear charge

Question 4

are anions or cations larger and why?

Answer 4

anions are larger because you are adding electrons instead of removing them

Question 5

explain the periodic trend in cationic radius across a period

Answer 5

decreases as cationic charge increases
because there are fewer electrons with a higher nuclear charge which pulls electrons closer

Question 6

explain the periodic trend in cationic radius down a group

Answer 6

increase down a group because atomic radius increases

Question 7

explain the periodic trend in anionic radius across a period

Answer 7

increases as anionic charge increases due to more electrons and lower nuclear charge attracting the electrons more weakly

Question 8

explain the periodic trend in anionic radius down a group

Answer 8

increases downs a group because atomic radius increases

Question 9

explain the periodic trend in ionisation energy across a period

Answer 9

increases due to the same shielding effect and higher nuclear charge attracting electrons more strongly, requiring more energy to remove an electron

Question 10

explain the periodic trend in ionisation energy down a group

Answer 10

decreases due to a higher shielding effect with the same nuclear charge attracting electrons less strongly requiring less energy to remove an electron

Question 11

define periodicity

Answer 11

repeating pattern or physical and chemical properties exhibited because of specific periodic trends

Question 12

what is an atomic radius?

Answer 12

distance from the nucleus to the valence electrons

Question 13

what is an ionic radius?

Answer 13

the distance from the nucleus to the outermost electron of a cation or anion

Question 14

what is electronegativity?

Answer 14

it is the relative measure of the attraction of an atom for the shared par of electrons

Question 15

define ionisation energy

Answer 15

energy required to remove one mole of electron from one mole of gaseous atoms

Question 16

define electron affinity

Answer 16

energy released when one mole of electrons is added to one mole of gaseous atoms

Question 17

explain the periodic trend in electron affinity down a group

Answer 17

decreases down the group because…
- increased shielding effect that outweighs the increase in nuclear charge
- so electrostatic attraction decreases
* note that fluorine does not fit the trend

Question 18

explain the periodic trend in electron affinity across a period

Answer 18

increases across a period because…
- increases in nuclear charge
- no change in shielding effect
- so the electrostatic attraction increases
* note that phosphorus does not fit the trend

Question 19

is the first electron affinity negative or positive and why? is this reaction favorable or not?

Answer 19

• it is negative
• as atoms generally want to gain electrons
• this reaction is favorable/ exothermic because its value is negative

Question 20

is the second electron affinity negative or positive and why? is this reaction favorable or not?

Answer 20

• it is positive
• as the negative ion created from the first electron affinity repels any additional electrons
• this reaction is less favorable/ endothermic because its value is positive

Question 21

describe the characteristics of the alkali metals

Answer 21

• soft very reactive metal elements
• down the group: reactivity increases and melting point decreases
• low melting and boiling point
• all react with oxygen and water

Question 22

what does alkali metal form when reacted with oxygen?

Answer 22

metal oxides

Question 23

what does alkali metal form when reacted with water?

Answer 23

form a metal hydroxide and hydrogen gas

Question 24

describe the characteristics of halogens

Answer 24

• diatomic non-metal elements
• down the group: reactivity decreases and melting point increases
• very low melting and boiling point
• all halogens reacts with alkali metals and halide solutions

Question 25

what does halogen form when reacted with alkali metal?

Answer 25

form white/ colourless neutral salts, which are soluble in water

Question 26

what does halogens form when reacted with halide solutions?

Answer 26

the more reactive halogen will displace the less reactive halogen

Question 27

how can the presence of halide ions be tested?

Answer 27

through the addition of silver nitrate solution

Question 28

how do you test for the presence of chloride ions and what are the observations?

Answer 28

• adding silver nitrate solution
• white precipitate will form

Question 29

how do you test for the presence of bromide ions and what are the observations?

Answer 29

• adding silver nitrate solution
• a cream precipitate will form

Question 30

how do you test for the presence of iodide ions and what are the observations?

Answer 30

• adding silver nitrate solution
• a yellow precipitate will form