Cliffs AP Chemistry, 3rd Edition

Samples: Free-Response Questions

1. The first three ionization energies (I 1 , I 2 , and I 3 ) for beryllium and neon are given in the
   following table:

(kJ/mole) I 1 I 2 I 3

Be 900 1757 14,840

Ne 2080 3963 6276

(a) Write the complete electron configuration for beryllium and for neon.

(b) Explain any trends or significant discrepancies found in the ionization energies for

beryllium and neon.

(c) If chlorine gas is passed into separate containers of heated beryllium and heated

neon, explain what compounds, if any, might be formed, and explain your answer in

terms of the electron configurations of these two elements.

(d) An unknown element, X, has the following three ionization energies:

(kJ/mole) I 1 I 2 I 3

X 419 3069 4600

On the basis of the ionization energies given, what is most likely to be the compound

produced when chlorine reacts with element X?

Answer

The outline format might work well in part (b).

1. Given: First three ionization energies of Be and Ne.
   (a) Restatement: Electron configuration of Be and Ne.
   Be: 1s^2 2s^2
   Ne: 1s^2 2s^2 2p^6

(b) Restatement: Significant trends/discrepancies in the first three ionization energies of

Be and Ne.

I. Note that in the case of both beryllium and neon, ionization energies increase as

one moves from I 1 to I 2 to I 3.

II. The general trend is for ionization energy to increase as one moves from left to

right across the periodic table and to decrease as one moves down; this is the in-

verse of the trend one finds in examining the atomic radius.

III. Note further that beryllium and neon are in the second period.

Part II: Specific Topics