CHEM 119 Exam Review: Atomic Structure, Bonding, Stoichiometry and Equilibrium

Terms in this set (30)

1. What do the atomic number and mass number represent?Atomic number (Z) is the number of protons. Mass number (A) is protons plus neutrons.
2. Isotopes vs ionsIsotopes have the same number of protons but different numbers of neutrons. Ions have gained or lost electrons and carry a net charge.
3. Relationship between wavelength, frequency and energy of lightc = lambda x nu and E = h x nu, where c is the speed of light, lambda the wavelength, nu the frequency, and h Planck's constant. Shorter wavelength means higher energy.
4. List the four quantum numbers and what each describes.n: energy level and size. l: subshell shape (0 = s, 1 = p, 2 = d, 3 = f). ml: orbital orientation (-l to +l). ms: electron spin (+1/2 or -1/2).
5. State the Pauli exclusion principle and Hund's rule.Pauli: no two electrons in an atom share all four quantum numbers, so an orbital holds at most 2 electrons of opposite spin. Hund: electrons fill degenerate orbitals singly with parallel spins before pairing.
6. Write the ground-state electron configuration of oxygen.1s2 2s2 2p4.
7. How do atomic radius and first ionization energy trend on the periodic table?Atomic radius decreases across a period and increases down a group. Ionization energy increases across a period and decreases down a group.
8. Why does atomic radius decrease across a period?Effective nuclear charge increases as protons are added while electrons enter the same shell, so electrons are pulled closer.
9. Ionic vs covalent bondsIonic bonds form from electrostatic attraction between ions after electron transfer (usually metal plus nonmetal). Covalent bonds share electron pairs between nonmetals.
10. How do you calculate formal charge?Formal charge = valence electrons - nonbonding electrons - (bonding electrons / 2). The best Lewis structure minimizes formal charges.
11. Give the VSEPR geometry for 4 electron domains with 0, 1 and 2 lone pairs.0 lone pairs: tetrahedral (CH4, 109.5 degrees). 1 lone pair: trigonal pyramidal (NH3). 2 lone pairs: bent (H2O).
12. Why is CO2 nonpolar even though C=O bonds are polar?CO2 is linear, so the two equal bond dipoles point in opposite directions and cancel.
13. What hybridization goes with 2, 3 and 4 electron domains?2 domains: sp (linear). 3 domains: sp2 (trigonal planar). 4 domains: sp3 (tetrahedral).
14. Sigma vs pi bondsA sigma bond results from head-on orbital overlap; every single bond is one sigma. A pi bond results from side-by-side p-orbital overlap; a double bond is 1 sigma + 1 pi, a triple bond is 1 sigma + 2 pi.
15. How many moles are in 36.0 g of water (molar mass 18.0 g/mol)?36.0 g / 18.0 g/mol = 2.00 mol.
16. What is a limiting reactant?The reactant that is completely used up first, which determines the maximum amount of product that can form.
17. How is percent yield calculated?Percent yield = (actual yield / theoretical yield) x 100.
18. Define molarity and give a dilution formula.Molarity M = moles of solute / liters of solution. Dilution: M1V1 = M2V2.
19. How much 6.0 M HCl is needed to make 500 mL of 1.5 M HCl?V1 = (1.5 M x 500 mL) / 6.0 M = 125 mL, diluted to 500 mL.
20. Ideal gas law and the meaning of each symbolPV = nRT. P: pressure, V: volume, n: moles, R: gas constant (0.08206 L atm / mol K), T: temperature in kelvin.
21. State Dalton's law of partial pressures.The total pressure of a gas mixture equals the sum of the partial pressures of each gas; each partial pressure = mole fraction x total pressure.
22. Rank the intermolecular forces from weakest to strongest (typical).London dispersion < dipole-dipole < hydrogen bonding. Ion-dipole forces are stronger still and occur in ionic solutions.
23. What is required for hydrogen bonding?An H atom covalently bonded to N, O or F, attracted to a lone pair on another N, O or F.
24. Write the equilibrium constant expression for aA + bB <-> cC + dD.K = [C]^c [D]^d / ([A]^a [B]^b). Pure solids and liquids are omitted.
25. Q vs K: how do you predict the direction of a reaction?If Q < K the reaction shifts forward toward products. If Q > K it shifts toward reactants. If Q = K it is at equilibrium.
26. State Le Chatelier's principle with an example.A system at equilibrium shifts to counteract a disturbance. Adding a reactant shifts the equilibrium toward products.
27. Bronsted-Lowry acid vs baseAn acid is a proton (H+) donor; a base is a proton acceptor. Removing H+ from an acid gives its conjugate base.
28. What is the pH of a 0.010 M HCl solution?HCl is a strong acid, so [H+] = 0.010 M and pH = -log(0.010) = 2.00.
29. Relationship between pH, pOH and Kw at 25 CKw = [H+][OH-] = 1.0 x 10^-14, so pH + pOH = 14.00.
30. Strong vs weak acidsStrong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4) ionize completely in water. Weak acids ionize only partially and are described by Ka.