The Top 79 Things You Need to Know
1. Qualitative data involves descriptions of things, while quantitative data involves
numbers.
2. The independent variable is the thing you change in an experiment, while the
dependent variable is the thing that happens as a result.
3. The SI base units are the meter, the kilogram, the second, the mole, the Pascal,
and Kelvin. Another important unit is called the liter (equal to 1 dm3).
4. Commonly used unit prefixes include mega (M: 1,000,000), kilo (k: 1,000), centi
(c: 0.01), and milli (m: 0.001).
5. Density = mass/volume.
6. Accuracy measures the trueness of a measurement and precision measures its
reproducibility.
7. Physical changes don’t change the chemical makeup of something, but chemical
changes (called “reactions”) do.
8. Homogeneous mixtures (“solutions”) have uniform composition, while
heterogeneous mixtures do not.
9. Common methods of separating mixtures include filtration, distillation,
crystallization, and chromatography.
10. Elements are materials that contain one type of atom, while compounds contain
one type of molecule.
11. Thompson’s cathode ray experiment discovered the electron and led to the plum
pudding model of the atom.
12. Rutherford’s gold foil experiment discovered the atomic nucleus.
13. The Bohr model of the atom sees electrons as “planets” around the nucleus (which
serves as the sun).
14. The number of protons in an atom is equal to the atomic number, the number of
neutrons is equal to (atomic mass – protons) and the number of electrons is equal
to (protons – charge of the atom).
15. Isotopes are forms of atoms that have different numbers of neutrons and, hence,
different weights.
16. Alpha radiation is when an atom gives off a 4He nucleus (called an alpha particle),
beta radiation is when an atom gives off an electron (called a beta particle),
gamma radiation is when an atom gives off energetic light, and positron emission
is when an atom gives off a positron (which is an electron with a positive instead of
a negative charge).
17. The lines given off in an atomic spectrum are due to the differences in energies
between the orbitals in an atom. All elements have a unique atomic spectrum, so
you can identify them by a process known as spectroscopy.
18. The electron configurations for each element can be found on the periodic table
provided to you on the SOL. It tells you where each of the electrons in the atom
can be found.
19. Mendeleev was the main guy who invented the modern periodic table. It’s
arranged in columns (called “groups” or “families”) that contain elements with
similar properties and rows (called “periods”) that contain elements whose outer
electrons have about the same amount of energy.
20. Important groups on the periodic table include: Alkali metals (group 1 – except
hydrogen, very reactive), alkaline earth metals (group 2, less reactive than the
alkali metals), transition metals (groups 3-12), halogens (group 17, very reactive
nonmetals), noble gases (group 18, unreactive), lanthanides and actinides (at the
bottom).
21. Metalloids have properties somewhere between those of metals and nonmetals.
22. Elements in the same group have similar properties because their electron
configurations are very similar.
23. Atomic radius decreases left to right across the periodic table and increases as you
move down the periodic table. Cations have smaller radii than neutral atoms and
anions have larger radii.
24. Ionization energy (the energy needed to pull off an electron) and electronegativity
(a measure of how much an atom grabs electrons from its neighbors) goes up as
you move across the periodic table and down as you go down a group.
25. The octet rule: All elements want to be like the nearest noble gas. Chemical
reactions occur so that this happens.
26. Ionic compounds are formed when one atom transfers its valence electrons to
another atom. They stick together like little magnets (an “ionic bond”).
27. Ionic compounds are hard, brittle, have high melting and boiling points, and
conduct electricity when dissolved/melted.
28. The properties of metals are due to their method of bonding, often known as the
“electron sea theory.” This theory states that the valence electrons in a metal can
move freely throughout the entire metal.
29. Covalent compounds are formed when two atoms share electrons (2 shared e - = 1
covalent bond)
30. Covalent compounds generally have low melting and boiling points and don’t
conduct electricity well.
31. Polar covalent bonds are covalent bonds in which one atom pulls the electrons
more tightly than another.
32. Chemical equations look like this: reactants  products. The law of conservation
of mass makes it necessary to balance these equations.
33. The main types of chemical reaction are: synthesis reaction (A + B  C),
combustion reactions (something + O2  CO2 + H2O), decomposition reactions (C
 A + B), single replacement reactions (A + BC  AC + B), double replacement
reactions (AB + CD  AD + CB) and acid-base reactions (HA + BOH  BA +
H2O).
34. 1 mole = 6.022 x 1023 things.
35. The empirical formula of a compound is the reduced molecular formula. For
example, the molecular formula C2H2 reduces to the empirical formula CH.
36. Hydrates are chemical compounds to which water molecules are loosely attached.
Heat can remove them.
37. The limiting reactant in a chemical process is the one that is used up first.
38. The theoretical yield is how much stuff stoichiometry predicts you should make in a
chemical reaction, while the actual yield is what you really made when you did the
experiment in the lab. Percent yield is a measure of how close the actual yield is
to the theoretical yield.
39. The kinetic molecular theory explains the behavior of gases and assumes that gas
molecules are infinitely small, constantly move in random directions until they hit
something, only change direction when they collide with something, lose no energy
when they hit other things (this is called an “elastic collision”), and have energies
proportional to their temperature (in Kelvin).
40. Barometers are used to measure gas pressure.
41. Dalton’s law of partial pressures: Ptot = P1 + P2 + …
42. Intermolecular forces are weak attractions between covalent molecules. London
dispersion forces are caused by temporary dipoles on nonpolar molecules, dipoledipole forces are caused by permanent dipoles on polar molecules, and hydrogen
bonds are attractions between the H atom on one molecule and the O, F, or N
atom on another.
43. Unit cells are the repeating patterns that make up crystal structures.
44. The melting point and freezing point of a compound are the same.
45. The phase transitions in a chemical compound are: melting  freezing, boiling 
condensing, sublimation  deposition. You can track the temperatures of each on
a phase diagram.
46. The triple point of a phase diagram shows where all three phases of matter are at
equilibrium. The critical point indicates the temperature at which the distinction
between a gas and liquid is lost.
PV
PV
47. The combined gas law: 1 1  2 2
T1
T2
48. The ideal gas law: PV = nRT.
49. All gases have the same volume under the same conditions of temperature,
pressure, and temperature. At STP (00 C and 1 atm), this is equal to 22.4 L.
50. Like dissolves like (polar solvents dissolve polar solutes, nonpolar solvents
dissolve nonpolar solutes, polar solvents don’t dissolve nonpolar solutes (or viceversa).
51. Unsaturated solutions can still dissolve more solute, saturated solutions have
dissolved the maximum possible quantity of solute, and supersaturated solutions
have dissolved more solute than they really should (so are unstable).
52. Gases increase in solubility as temperature decreases, solids increase in solubility
as temperature increases.
53. Molarity (M) = moles of solute / L of solution; molality (m) = moles of solute / kg of
solvent.
54. In dilutions, M1V1 = M2V2
55. When you dissolve stuff in a liquid, it causes the melting point to go down and the
boiling point to go up. The more stuff you dissolve, the bigger then change.
56. Electrolytes are liquids that conduct electricity.
57. Suspensions are mixtures where stuff eventually settles to the bottom, colloids are
mixtures that contain two phases where nothing eventually settles (due to
Brownian motion), and solutions are homogenous mixtures in which it’s impossible
to tell by inspection that anything’s dissolved at all.
58. Energy is never created or destroyed, but can change from one form to another.
When thermal energy moves around, this is called heat. Temperature is used to
measure the kinetic energies of particles in motion.
59. The specific heat of a material is the amount of energy required to heat 1 gram of it
by 10 C.
60. Calorimeters are devices used to measure the energy changes during chemical
reactions.
61. Enthalpy is the heat content of a system. If ∆H is positive a reaction is
endothermic, if it is negative is exothermic.
62. Hess’s Law says that the overall energy change from a series of reactions is equal
to the sum of the totals of each individual energy change.
63. Entropy is a measure of randomness.
64. Gibbs free energy is a thermodynamic quantity that measures whether a process is
spontaneous. If ∆G is negative a reaction is spontaneous and if it’s positive it’s
not.
65. The activation energy of a reaction is the amount of energy needed for it to occur.
Catalysts speed up reaction rates by lowering the activation energies of chemical
reactions.
66. Chemical reactions can be sped up by using more reactive reagents, by increasing
reactant concentration, by grinding up the reactants, by raising the temperature, or
by using catalysts.
67. Equilibria occur when a reaction can go both forwards and backwards. At
equilibrium, the rate of the forward reaction is the same as the rate of the reverse
reaction. Though the concentrations of product and reactant don’t change,
equilibrium is a dynamic process (i.e. the reactions are still occurring).
68. Le Châtlier’s principle: If you mess with an equilibrium, the equilibrium will shift to
undo whatever it is you did.
69. Arrhenius acids give off H+ ions and Arrhenius bases give off OH- ions. BrønstedLowry acids give off H+ ions and Brønsted-Lowry bases absorb them.
70. Water can be either an acid or a base: H2O  H+ + OH-.
71. pH = -log[H+]. pOH = -log[OH-]. pH + pOH = 14.
72. Indicators are compounds that are one color in acid and another color in base.
Well known ones are litmus (red in acid, blue in base) and phenolphthalein
(colorless in acid, pink in base).
73. Acidic solutions have a pH < 7, neutral solutions have a pH = 7.00000, and basic
solutions have a pH > 7.
74. Titrations are used to find the concentrations of acids and bases. The equation
used is M1V1 = M2V2.
75. Buffers are chemicals that keep the pH of a concentration from changing much
when acid or base are added.
76. Oxidation is when an atom loses electrons, while reduction is when an atom gains
them. LEO says GER.
77. Redox reactions are reactions in which one element is oxidized and another is
reduced.
78. Organic compounds contain carbon and hydrogen. They may also contain smaller
amounts of other elements.
79. Nuclear fusion is when small nuclei combine to form bigger ones and nuclear
fission is when a large nucleus breaks apart to form two smaller ones. Both create
lots of energy.