CHEM 101 Exam Review: Atomic Structure, Bonding, Gases and States of Matter

Terms in this set (35)

1. Photon energy formula and what each symbol meansE = h·v = h·c/λ. E is the photon energy in J, h is Planck's constant (6.626 x 10^-34 J·s), v is the frequency in s^-1, c is the speed of light (3.00 x 10^8 m/s) and λ is the wavelength in m.
2. What key observation of the photoelectric effect supports the particle nature of light?Electrons are ejected only when the light's frequency is above a threshold, no matter how intense it is. Raising the intensity raises the number of electrons, not their kinetic energy.
3. de Broglie wavelength formulaλ = h/(m·v), where m is the mass in kg and v is the velocity in m/s. It is only significant for very small particles such as electrons.
4. Energy levels of the hydrogen atom in the Bohr modelE_n = -2.18 x 10^-18 J (1/n^2). When an electron drops from a higher n to a lower n, a photon is emitted whose energy equals the difference between the two levels.
5. List the four quantum numbers and their allowed values.n = 1, 2, 3... (shell and size); l = 0 to n-1 (subshell shape: s, p, d, f); ml = -l to +l (orbital orientation); ms = +1/2 or -1/2 (electron spin).
6. How many orbitals and how many electrons can the n = 3 shell hold?It has n^2 = 9 orbitals (one 3s, three 3p and five 3d), so it can hold 2n^2 = 18 electrons.
7. Aufbau principle, Pauli exclusion principle and Hund's ruleAufbau: fill the lowest-energy orbitals first. Pauli: no two electrons in an atom share all four quantum numbers, so each orbital holds at most 2 electrons of opposite spin. Hund: in degenerate orbitals, electrons occupy separate orbitals with parallel spins before pairing.
8. Write the electron configurations of Fe and Fe3+.Fe: [Ar] 4s2 3d6. Fe3+: [Ar] 3d5. Transition metals lose their 4s electrons before their 3d electrons.
9. Which two common first-row transition metals have exceptional electron configurations?Cr is [Ar] 4s1 3d5 and Cu is [Ar] 4s1 3d10. A half-filled or filled d subshell gives them extra stability.
10. What is effective nuclear charge, and how does it change across a period?Zeff = Z - S: the nuclear charge an electron actually feels after shielding by inner electrons. It increases across a period because protons are added while shielding by same-shell electrons is weak.
11. Periodic trend in atomic radiusRadius decreases from left to right across a period (higher Zeff pulls the electrons in) and increases going down a group (electrons occupy higher shells).
12. Periodic trend in first ionization energy, and the main exceptionsIt generally increases across a period and decreases down a group. Exceptions: group 13 is lower than group 2 (for example B < Be, because a p electron is removed) and group 16 is lower than group 15 (O < N, because of pairing repulsion).
13. Rank O2-, F-, Na+ and Mg2+ by size.O2- > F- > Na+ > Mg2+. They are isoelectronic (10 electrons each), so the ion with the most protons pulls the electrons in most tightly and is smallest.
14. How does electronegativity difference predict bond type?Little or no difference (under about 0.4) gives a nonpolar covalent bond. A moderate difference gives a polar covalent bond. A large difference (roughly above 1.7 to 2) gives a mostly ionic bond. The cutoffs are approximate.
15. Formal charge formulaFormal charge = (valence electrons) - (nonbonding electrons) - (1/2)(bonding electrons). The best Lewis structure keeps formal charges near zero, with any negative charge on the more electronegative atom.
16. What are resonance structures?Two or more valid Lewis structures that differ only in where the electrons are placed. The real molecule is a hybrid of them; for example, both O-O bonds in ozone are identical, with a bond order of 1.5.
17. Which atoms can have an expanded octet?Atoms from period 3 and below, such as P, S, Cl and Xe, which can hold more than 8 valence electrons (for example PCl5, SF6 and XeF4). Period 2 atoms such as C, N and O cannot.
18. VSEPR: geometry of a molecule with 4 electron domains, 2 of them lone pairs (for example H2O)The electron-domain geometry is tetrahedral and the molecular shape is bent. The angle is about 104.5°, smaller than 109.5° because lone pairs repel more strongly.
19. What is the molecular shape of SF4?Seesaw. S has 5 electron domains (trigonal bipyramidal) with one lone pair, which sits in an equatorial position.
20. What is the molecular shape of XeF4?Square planar. Xe has 6 electron domains (octahedral) with two lone pairs placed opposite each other.
21. Why is CO2 nonpolar even though its C=O bonds are polar?It is linear, so the two equal bond dipoles point in opposite directions and cancel, giving no net dipole moment.
22. How do you match hybridization to electron domains, and what are sigma and pi bonds?2 domains: sp; 3: sp2; 4: sp3. A single bond is one sigma bond. A double bond is one sigma and one pi bond. A triple bond is one sigma and two pi bonds.
23. Molecular orbital bond order, and why O2 is paramagneticBond order = (bonding electrons - antibonding electrons)/2. O2 has a bond order of 2 and two unpaired electrons in degenerate pi* orbitals, so it is attracted to a magnetic field.
24. Ideal gas law and the units to usePV = nRT. Use R = 0.08206 L·atm/(mol·K) with P in atm and V in L, or R = 8.314 J/(mol·K) with SI units. T must always be in kelvin.
25. What is the pressure of 2.00 mol of an ideal gas at 300 K in a 10.0 L container?P = nRT/V = (2.00)(0.08206)(300)/10.0 = 4.92 atm.
26. Dalton's law of partial pressuresP_total = P1 + P2 + ... The partial pressure of each gas equals its mole fraction times the total pressure: P_i = x_i · P_total.
27. Kinetic molecular theory: what does temperature tell you about gas particles?Average kinetic energy is proportional to absolute temperature. Root-mean-square speed is u_rms = sqrt(3RT/M), where R = 8.314 J/(mol·K) and M is the molar mass in kg/mol, so lighter gases move faster.
28. Graham's law of effusionrate1/rate2 = sqrt(M2/M1). For example, H2 (2 g/mol) effuses about 4 times faster than O2 (32 g/mol), because sqrt(32/2) = 4.
29. When do real gases deviate most from ideal behaviour, and what do the van der Waals constants represent?At high pressure and low temperature. The constant a corrects for attractions between molecules (which lower the pressure) and b corrects for the volume the molecules themselves occupy.
30. Name the main intermolecular forces from generally weakest to strongest.London dispersion forces (present in all molecules), dipole-dipole forces (polar molecules) and hydrogen bonding (H bonded to N, O or F interacting with a lone pair on N, O or F). Ion-dipole forces are stronger still.
31. Why do boiling points increase going down the noble gases from He to Xe?Larger atoms have bigger, more polarizable electron clouds, so London dispersion forces get stronger and more energy is needed to separate the atoms.
32. Phase diagram: what are the triple point and the critical point?At the triple point, solid, liquid and gas coexist in equilibrium. Above the critical temperature and pressure, liquid and gas can no longer be told apart and the substance is a supercritical fluid.
33. When does a liquid boil?When its vapour pressure equals the external pressure. That is why water boils below 100 °C at high altitude, where the air pressure is lower.
34. Four types of solids and an example of eachIonic (NaCl: brittle, high melting point), molecular (ice, dry ice: low melting point), covalent network (diamond, quartz: very hard, very high melting point) and metallic (Cu: conductive, malleable).
35. Why are alkali metals so reactive?They have a single ns1 valence electron and a very low first ionization energy, so they readily form +1 ions. They react with water to form a hydroxide and H2 gas, and reactivity increases down the group.