Chem 101L: IMF and Molecular Modeling

What does a line represent in a Lewis structure?

A line represents a 2-electron covalent bond.

How are nonbonding electrons shown in Lewis structures?

As dots on the atom.

How do you determine total valence electrons for a Lewis structure of an ion?

Add valence electrons of all atoms, subtract charge for cations, add electrons for anions.

What is the octet rule?

Atoms are most stable when they have 8 electrons around them (except H, which can only have 2).

What is a condensed structural formula?

A shorthand notation showing grouped atoms without full Lewis structure detail.

In line structures, where are carbons located?

At line ends and bends.

In line structures, when are hydrogens shown?

Only when bonded to non-carbon atoms; otherwise implied.

What determines VSEPR shape

The number of electron domains (bonding + lone pairs) on the central atom.

Shape of: 4 electron domains, 0 lone pairs?

Tetrahedral.

Shape of: 4 electron domains, 1 lone pair?

Trigonal pyramidal.

Shape of: 3 electron domains, 1 lone pair?

Bent.

Shape of: 2 electron domains?

Linear.

How do lone pairs affect bond angles?

Lone pairs compress bond angles (repel more strongly than bonds).

What suffix indicates single carbon–carbon bonds?

–ane (alkane).

What suffix indicates a carbon–carbon double bond?

–ene (alkene).

What suffix indicates a carbon–carbon triple bond?

–yne (alkyne).

What suffix indicates an alcohol?

–ol.

What does the prefix cyclo- mean?

The molecule forms a ring.

What are structural isomers?

Molecules with the same formula, but different structures.

What are the 5 major types of IMFs?

• Electrostatic interactions

• Ion–dipole

• Dipole–dipole

• Hydrogen bonding

• London dispersion (induced dipole)

What molecules can participate in hydrogen bonding?

Molecules with H bonded to N, O, or F.

Are intermolecular forces stronger or weaker than covalent bonds?

Much weaker.

What type of IMF is present in nonpolar molecules?

London dispersion forces.

How does molecular size affect London dispersion forces?

More electrons → stronger dispersion forces.

How does branching affect dispersion forces?

More branching → weaker dispersion forces (less surface contact).

What is vaporization?

Transition from liquid to gas, requiring energy input

Is vaporization endothermic or exothermic?

Endothermic (requires energy).

What is ΔHvap (enthalpy of vaporization)?

The minimum energy required for a molecule to escape from liquid to gas.

What is the equation for kinetic energy?

KE = ½ m v²

What effect does strong IMF have on ΔHvap?

Stronger IMF → higher ΔHvap → slower evaporation.

What is evaporative cooling?

High-energy molecules leave → average KE decreases → temperature drops.

What distribution describes molecular velocities?

The Maxwell–Boltzmann distribution.

What does hybridization influence?

Bond angles and molecular geometry.

Do double and triple bonds count as 1 or multiple electron domains in VSEPR?

They count as one domain.

What factors can affect measured vs. predicted bond angles?

• Lone pairs
• Branching
• Atom size
• Hybridization

What do molecular models help visualize?

3D geometry, bond angles, and relationships between structure and IMF strength.