IB Chemistry melting point periodic trends

Practice Question Solving
1

Which of the following statements are correct?
I. The melting points decrease from Li → Cs for the alkali metals.
II. The melting points increase from F → I for the halogens.
III. The melting points decrease from Na → Ar for the period 3 elements.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III

hi
the correct answer is A)
i understand II) F is a gas and I is a solid so the melting point increases down

for I) i thought the opposite, Cs is bigger so has more surface area to have weak IMF keeping the compound solid so it has a higher melting point

for III) i tohught the opposite, Ar is a gas so the melting point is much lower

what is wrong with my reasoning??

2

I. Down group I Melting & Boiling decrease (Larger Radii)
II. Down group 7 Melting & Boiling increase (Greater IMF)
III. Across Periodic Table Melting & Boiling Increase

1 & II Correct

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3

hey
I)as you go down group one the atomic radius increases (inner core electron increases) because inner core electron increase this causes repulsive forces between electrons and push valance electron further so the attraction decreases .
II)melting point across period 3 varies it increase than decrease .
memorizing the trend could save you alot of time.

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