Inorganic Unit 2.1: Periodicity

Question 1

define periodicity

Answer 1

the pattern in properties across a row, which is repeated in each row

Question 2

how are elements classified as s, p or d block?

Answer 2

according to their proton number
& which orbitals the highest energy e-s are in

Question 3

what is the trend in atomic radius across a period & why?

Answer 3

atomic radius decreases across a period
increase in # of protons
same shielding
outer e- in same principle energy level
stronger attraction b/w outer shell e-s & nucleus, pulling the e-s in

Question 4

what is the general trend in 1st ionisation energy across a period & why?

Answer 4

of protons increases

general trend: ionisation energy increases across period
atomic radius decreases
same shielding
so stronger attraction b/w outer shell e-s & nucleus
it takes more energy to remove it

Question 5

what groups deviate from the general increase in IE across the period & why?

Answer 5

group 2–>3 dip
1IE of Al<Mg
Mg: 1s2 2s2 2p6 3s2
the outer e- in Mg is in an s orbital
al: 1s2 2s2 2p6 3s2 3p1
Al outer e- is in a p orbital
p orbital is higher in energy than s orbital
so less energy needed to remove the outer e- in Al

group 5–>6 dip
1IE of S<P
p: 1s2 2s2 2 p6 3s2 3p3
P outer e- is from an orbital with one e-
s: 1s2 2s2 2p6 3s2 3p4
S outer e- is from an orbital with 2 e-s paired up, which repel each other
so less energy is needed to remove outer e- in S

Question 6

what is the trend in electronegativity across a period & why?

Answer 6

electronegativity increases
bc increase in # of protons
atomic radius decreases
same shielding
so stronger attraction b/w nucleus & the 2e-s in covalent bond

Question 7

what is the trend in melting & boiling point across a period & why?
split into 4 parts

Answer 7

1. Na, Mg, Al (metals)
   higher mp & bp bc strong metallic bonding
   Al>Mg>Na bc from Na–>Al ion size decrease, positive charge of ion increases & # of delocalised e-s increases
2. Si
   highest mp & bp in period bc macromolecular/giant covalent structure
   lots of thermal energy is needed to break v many v strong covalent bonds
3. P4, S8, Cl2
   low mp & bp bc simple molecular strucures
   weak Van der Waal’s forces b/w molecules
   S8>P4>Cl2 bc S8 biggest & has most e-s so strongest VDWs b/w molecules
   decrease in # of e-s = weaker VDWs
4. Ar
   lowest mp & bp bc monatomic
   weakest VDW b/w atoms