Chemistry Bonding, Intermolecular Forces, Phase Changes, and Hydrocarbons

What determines bond polarity?

Difference in electronegativity between bonded atoms.

What is a nonpolar covalent bond?

Bond between atoms with similar electronegativity (e.g., H-H, C-C).

What is a polar covalent bond?

Bond between different nonmetals with unequal electron sharing (e.g., O-H).

What is an ionic bond?

Electron transfer between a metal and a nonmetal (e.g., NaCl).

When is a molecule polar?

When it has polar bonds AND an asymmetrical geometry.

Why is CO₂ nonpolar?

Linear geometry causes bond dipoles to cancel.

Why is NH₃ polar?

Trigonal pyramidal shape creates a net dipole.

What is the order of intermolecular forces from weak to strong?

London dispersion < dipole-dipole < hydrogen bonding < ion-dipole.

What are London dispersion forces?

Temporary dipoles present in all particles; strength increases with molecular size.

What are dipole-dipole forces?

Attractions between permanent dipoles in polar molecules.

What is hydrogen bonding?

Strong dipole-dipole attraction when H is bonded to N, O, or F.

Do C-H bonds allow hydrogen bonding?

No; hydrogen bonding requires H bonded to N, O, or F.

What properties increase with stronger intermolecular forces?

Boiling point, melting point, specific heat.

What happens to temperature during a phase change?

Temperature remains constant.

What is the equation for heat when temperature changes?

q = mcΔT.

What is the equation for heat during a phase change?

q = mΔH.

What is the difference between melting and freezing?

Melting absorbs heat; freezing releases heat.

What is the difference between vaporization and condensation?

Vaporization absorbs heat; condensation releases heat.

Why is ΔH_vap larger than ΔH_fus?

More energy is required to separate molecules into gas.

What does a sloped line on a heating curve indicate?

Temperature is changing; use q = mcΔT.

What does a flat line on a heating curve indicate?

Phase change; use q = mΔH.

What does a phase diagram show?

Stable phases of a substance as a function of temperature and pressure.

What is the triple point?

Point where solid, liquid, and gas coexist.

What is the critical point?

End of the liquid-gas boundary; beyond it is a supercritical fluid.

What is the normal boiling point?

Temperature where liquid and gas are in equilibrium at 1 atm.

What is the effect of increasing pressure on phase?

Favors condensed phases (solid or liquid).

What is unique about water's phase diagram?

Solid-liquid line slopes left because ice is less dense than liquid water.

What is an alkane?

Saturated hydrocarbon with only single bonds.

What is the general formula for alkanes?

CₙH₂ₙ₊₂.

What is an alkene?

Unsaturated hydrocarbon with one C=C double bond.

What is the general formula for alkenes?

CₙH₂ₙ.

What is an alkyne?

Unsaturated hydrocarbon with one C≡C triple bond.

What is the general formula for alkynes?

CₙH₂ₙ₋₂.

What is the general formula for cycloalkanes?

CₙH₂ₙ.

What is an aromatic hydrocarbon?

Benzene and its derivatives only.

Stronger intermolecular force means?

Higher boiling point

Higher melting point

Higher specific heat

Lower vapor pressure

Lower volatility

endothermic phase changes

melting, vaporization, sublimation

exothermic phase changes

freezing, condensation, deposition