AP Chemistry - Unit 2 Review

Answer explanation

Ionic substances will have high melting points due to their high lattice energy.

Tags

NGSS.HS-PS1-3

Which of the following molecules is nonpolar?

• HF

Answer explanation

Though the C-F bond will be very polar due to the difference in electronegativity, the symmetry of this molecule makes it nonpolar.

Which of the following substances will have the highest melting point? Hint - think about lattice energy and Coulomb's Law.

• NaCl

• NaF

Answer explanation

Magnesium has a larger charge (+2) compared to sodium (+1). The fluorine ion will be much smaller than chlorine, and therefore, the ions will be more tightly packed (and harder to separate) in MgF2.

Tags

NGSS.HS-PS1-3

NGSS.HS-PS2-4

Bronze is a(n) ______ alloy.

• Interstitial

• Intertwined

• Substitutional

• Substertial

Determine the formal charge on the central atom of the nitrate ion.

• +1

• 0

• -1

• -2

Answer explanation

To determine formal charge, remember:

valence - "dots" - "sticks"

valence electrons - lone pairs - (bonded electrons/2)

For this ion, nitrogen is the central atom:

5 valence - 0 lone pairs - 4 bonds = 1

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Phosphorus pentachloride will have which molecular geometry?

• Trigonal planar

• Trigonal pyramidal

• Trigonal bypyramidal

• Octahedral

Answer explanation

Memorize these geometries!

What is the bond hybridization of the central carbon in dichloromethane?

• sp

Answer explanation

To determine hybridization, count the total number of bonds and lone pairs on the central atom.

The carbon atom in CH2Cl2 has 4 bonds and no lone pairs; therefore, it has sp3 hybridization.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

How many pi bonds are in capsaicin?

• 24

• 23

• 4

• 5

Answer explanation

single bond - 1 sigma bond

double bonds - 1 sigma + 1 pi

triple bonds - 1 sigma + 2 pi

Tags

NGSS.HS-PS1-2

Draw a Lewis structure for C2H4.

Answer explanation

Keep practicing with Lewis structures. The more you do, the easier both this and geometry will be!

Which molecule will not have resonance structures?