Question

Which of the following is most likely to be a covalently bonded, polar compound?

Question 6 options:

NaCl

NH 3

CCl 4

CH 4

Which of the following compounds is a molecule?
Question 7 options:

AlCl 3

H 2

NaCl

MgBr 2

Answer 1

Question 6

NH₃

• NaCl contains Na, a group 1 metal bonded to Cl, a group 17 halogen. The electronegativity difference between Na and Cl is so large that the two atoms become ions. NaCl would contain ionic bonds rather than covalent bonds.
• Both N and H are nonmetals and form covalent bonds. As a result, NH₃ is a covalently bonded compound. N-H bonds are polar. The shape of NH₃ molecules is asymmetric. Dipoles won't cancel out within the molecule. NH₃ is therefore polar.
• Molecules of CCl₄ and CH₄ are symmetrical. Dipoles within both molecules would cancel out. Their molecules will not be polar.

Question 7

H₂

A compound can be a molecule, a giant covalent crystal, or an ionic crystal. The exact type of the compound depends the difference between electronegativities of its atoms.

• A compound with two nonmetals elements (H, O, N, F, Cl, etc.) tend to be a molecule.
• A nonmetal element combine and a metal element tend to produce an ionic crystals.
• Group 14 metalloids (C and Si) tend to form giant covalent crystal.

All four compounds excepting for H₂ are ionic crystals.