Periodic trends and bonding models

Written by Dr. Ayesha Nadeem (Chemistry)

ECAT · Chemistry · 5 questions

Name: ____________________ Date: ____________

Which ionic compound has the highest lattice energy?
- A MgO
- B NaCl
- C KBr
- D NaBr
What is the bond order of the O2 molecule according to molecular orbital theory?
- A 2
- B 3
- C 2.5
- D 1
What is the shape of the ammonium ion, NH4+?
- A Linear
- B Square planar
- C Trigonal pyramidal
- D Tetrahedral
Which of these molecules has zero dipole moment?
- A NH3
- B CHCl3
- C H2O
- D CCl4
How many lone pairs of electrons are on the oxygen atom in a water molecule?
- A 1
- B 4
- C 3
- D 2

Answer key

1. A, 2. A, 3. D, 4. D, 5. D

Lattice energy is greatest for ions with high charges and small radii. MgO has 2+ and 2- ions.
O2 has 8 bonding and 4 antibonding electrons in the valence orbitals, so bond order = (8 - 4) / 2 = 2.
Nitrogen has four bond pairs and no lone pairs, giving a tetrahedral shape.
In CCl4 the four polar bonds are arranged symmetrically in a tetrahedron, so the dipoles cancel.
Oxygen has six valence electrons. Two are used in bonds and the remaining four form two lone pairs.