3.2.1 - periodicity

Question 1

how are elements in the periodic table classified?

Answer 1

as s, p, d or f block, according to their position in the table (which is based on proton number)

Question 2

which areas of the periodic table table does each block cover?

Answer 2

s block - groups 1 and 2, and helium
d block - transition metals
p block - groups 3, 4, 5, 6, 7 and the noble gases (excluding helium)
f block - separate elements at the bottom

Question 3

what is the trend in elecronegativity for the period 3 elements from Na-Ar?

Answer 3

elecronegativity increases across the period because the nuclear charge increases, so the ability of the atom to attract the bonding pair of electrons in the covalent bond increases

Question 4

what is the trend in atomic radius for the period 3 elements from Na-Ar?

Answer 4

atomic radius decreases because the atoms of each element have one more proton than for the element before (nuclear charge increases), so the nucleus attracts the energy levels more strongly, so they are closer to the nucleus

Question 5

what is the trend in 1st IE for the period 3 elements from Na-Ar?

Answer 5

overall trend is that it increases because although the atomic radius and therefore shielding remains similar, the nuclear charge increases, so the nucleus attracts the outer electron more strongly
exceptions:
Al has lower 1st IE than Mg - outer electron removed from a higher energy 3p sub-level so it is less strongly attracted to nucleus
S has lower 1st IE than P - has paired electrons in a 3p orbital and they repel each other

Question 6

what is the trend in melting points for the period 3 elements from Na-Ar?

Answer 6

melting point increases from Na to Al- nuclear charge increases, so the strength of the metallic bonds increases because there is a greater attraction between the positive ions and delocalised electrons (and more delocalised electrons)
Si has highest melting point because it has a giant covalent structure where Si atoms are held to neighbouring atoms by 4 strong covalent bonds
melting point decreases overall from P to Ar, but increases from P to S (all have simple molecular structures)
S has largest molecules (S8), then P (P4), then Cl (Cl2), then Ar (single atom), so the van der Waals forces between molecules become smaller as the size of the molecule decreases
order from highest to lowest is Si, Al, Mg, S, Na, P, Cl, Ar - note that S has a higher melting point than Na, because its molecules are so large that he van der Waals forces between molecules are stronger than the metallic bonds present in Na