Question

ionization energy
3rd period elements
the data table represents the ionization energy for some elements in the 3rd period. it includes na, mg, si, p, cl, and ar.
consider the data below and your knowledge of subatomic particle interactions.

element sample | ie (kj/mole)
--- | ---
1 | 1520
2 | 1251
3 | 786
4 | 1011
5 | 496
6 | 737

which element sample represents si?

• element 3
• element 2
• element 6
• element 4

Explanation:

Step1: List known IE trends (3rd period)

Ionization energy (IE) generally increases left-to-right across a period, with exceptions: Mg > Al (full 3s orbital), P > S (half-full 3p orbitals). For 3rd period elements given: Na < Mg < Si < P < Cl < Ar (IE order, kJ/mol approx: Na=496, Mg=737, Si=786, P=1011, Cl=1251, Ar=1520).

Step2: Match Si to sample value

Si's IE is ~786 kJ/mol, which matches Sample 3.

Answer:

element 3