A-LEVEL CHEMISTRY: 3.2.1: Periodicity (ChemRevise & PMT)

Question 1

periodicity:

Answer 1

periodicity is the repeating pattern of chemical or physical properties, across the periods

Question 2

elements are classified as…
what is this according to?

Answer 2

s, p, d, f blocks
according to which orbital the highest energy electrons are in

Question 3

as you go across a period, atomic radius…

Answer 3

decreases

Question 4

what is the general trend for atomic radius across a period? explain it: (4)

Answer 4

decreases

because:
-nuclear charge increases (more protons)

-same number of electron shells across a period, so similar shielding

-increased nuclear attraction pulls outermost electrons closer to the nucleus

Question 5

what is the general trend for first ionisation energy across a period?

Answer 5

increases

Question 6

what is the general trend for first ionisation energy across a period? explain: (5)

Answer 6

increases

because:
-nuclear charge increases (more protons)

-outermost electrons experience stronger nuclear attraction

-shielding remains similar

-so more energy is required to remove valent electrons

Question 7

what are the two exceptions to the general trend in first ionisation energy across period 3? (2)
explain them: (6)

Answer 7

• Al lower than Mg
  because:
  -Al valent electron is in p-orbital (higher energy)

-further away from the Nucleus

-so requires less energy to remove from the atom

• S lower than P
  because:
  -S valent electrons are paired in p-orbital

-so they naturally Repel each other

-so less energy is needed to remove from the atom

Question 8

explain the first exception in the trend for first ionisation energy across a period: (4)

Answer 8

-between Group 2 & 3, eg Al lower than Mg

because:
-Al valent electron is in p-orbital (higher energy)

-further away from the nucleus

-so requires less energy to remove from the atom

Question 9

explain the second exception in the trend for first ionisation energy across period 3. (4)

Answer 9

-S lower than P

because:
-S valent electrons are paired in p-orbital

-so they naturally repel each other

-so less energy is needed to remove from the atom

Question 10

as you go across a period, first ionisation energy…

Answer 10

GENERALLY increases

Question 11

explain the trend in melting & boiling points across period 3: (4)

Answer 11

-metals (groups 1-3) (Na, Mg, Al): MP & BP increase. stronger metallic bonds, as charge & number of delocalised electrons Increase

-silicon, Si (group 4): highest MP & BP, giant covalent structure

-simple molecular structures (Groups 5-7)(P, S, Cl) : MP & BP decrease, due to weak Van der Waals forces. CLUSTERS

-noble gases (group 8)(argon, Ar): lowest MP & BP. monatomic, weak Van der Waals Forces