Chem 101 exam 3

Exothermic reaction

A reaction that releases heat to the surroundings; temperature of surroundings increases; ΔH < 0.

Endothermic reaction

A reaction that absorbs heat from the surroundings; temperature of surroundings decreases; ΔH > 0.

Potential energy (PE)

Stored energy in chemical bonds; on the y-axis of a reaction coordinate diagram.

Activation energy (Ea)

Minimum energy needed for reactants to reach the transition state and form products.

Exothermic reaction diagram

Products have lower potential energy than reactants; energy is released.

Endothermic reaction diagram

Products have higher potential energy than reactants; energy is absorbed.

Dalton’s atomic theory

Atoms are indivisible and combine in whole number ratios; atoms of each element are identical.

Thomson’s model

Discovered the electron; proposed the plum pudding model.

Rutherford’s model

Discovered the nucleus via gold foil experiment; atom is mostly empty space.

Bohr’s model

Electrons exist in quantized energy levels; explains line spectra.

Quantized energy levels

Electrons can only occupy specific allowed energy values.

Continuous energy

Energies vary smoothly; produces continuous spectrum.

Orbital

Region of space with high probability of finding an electron.

s orbital

Spherical orbital holding 2 electrons.

p orbital

Three dumbbell-shaped orbitals holding 6 electrons total.

d orbital

Five orbitals holding 10 electrons total.

f orbital

Seven orbitals holding 14 electrons total.

Aufbau principle

Electrons fill lowest-energy orbitals first.

Atomic radius trend (period)

Radius decreases left → right due to increased nuclear charge pulling electrons closer.

Atomic radius trend (group)

Radius increases going down due to more electron shells and shielding.

Ionization energy trend (period)

IE increases left → right as nuclear charge increases.

Ionization energy trend (group)

IE decreases down a group because electrons are farther and more shielded.

Electronegativity trend (period)

EN increases left → right due to increasing nuclear attraction.

Electronegativity trend (group)

EN decreases down a group as atoms get larger and attract electrons less.

Isoelectronic series

Atoms/ions with same number of electrons; more protons = smaller radius.

Resonance structures

Valid Lewis structures differing only in placement of electrons; atoms stay in same positions.

Example of resonance in CO2

CO2 has O=C=O and charge-separated resonance forms.

Nonpolar molecules (CO2, NF3, IF3, SF4, XeCl4)

CO2 and XeCl4 are nonpolar.

Molecule with no 180° bond angles

NF3.

Molecules capable of resonance from list

CO2 only.