Groups 1,2, and 13-18 in the periodic table. They're called
main block elements because the outermost electron is in the s-
or p- orbitals. What that has to do with the term "main
block" is unclear to me, but hey, that's life.
The difference between the mass of an atom and the sum of the
masses of its individual components. Atoms usually weigh a
little less than if you added up the weights of all the
particles. This is because that extra mass was converted
into the energy which holds the atom together (see "binding
The amount of matter in an object. The more mass, the more
stuff is present.
A step-by-step sequence that shows how the products of a reaction
are made from the reagents. Mechanisms are very frequently
shown during organic chemistry.
The number of moles of solute per kilogram of solvent in a
solution. This is a unit of concentration that's not
anywhere near as handy or common as molarity.
The mass of one mole of particles.
The volume of one mole of a substance at STP. If you
believe that everything is an ideal gas, this is always 22.4
liters. Unfortunately, there's no such thing as an ideal
A unit of concentration equal to moles of solute divided by
liters of solution.
The number of moles of stuff in a mixture that are due to one of
The ratio of moles of what you've been given in a reaction to
what you want to find. Handy in stoichiometry.
6.02 x 1023
A compound held together by covalent bonds.
A formula that shows the correct quantity of all of the atoms in
An ion that has only one atom, like the chloride ion.
The reaction of an acid with a base to form water and a salt.
A location in an orbital where there's no probability of finding
A covalent bond where the electrons are shared equally between
the two atoms.
The boiling point of a substance at 1.00 atm.
The melting point of a substance at 1.00 atm.
The number of equivalents of a substance dissolved in a liter of
When many small atoms combine to form a large one. This
occurs during a thermonuclear reaction.
This is when the nucleus of an atom breaks into many parts.
Any reaction that involves a
change in the nucleus of an atom. Nuclear reactions take
loads of energy, which is why you don't see them much around the
A particle (such as proton or neutron) that's in the nucleus of
All atoms want to be like the nearest noble gas. (Well,
they all want to have the same number of valence electrons,
anyway). To do this, they either gain or lose electrons (to
form ionic compounds) or share electrons (to form covalent
Isomerism in which the isomers cause plane polarized light to
rotate in different directions.
This is where the electrons in an atom live.
compound that contains carbon (except carbon dioxide, carbon
monoxide, and carbonates)
The flow of a pure liquid into an area of high concentration
through a semi-permeable membrane.
The apparent charge on an atom.
When a substance loses electrons.
The pressure of one gas in a mixture. For example, if you
had a 50:50 mix of helium and hydrogen gases and the total
pressure was 2 atm, the partial pressure of hydrogen would be 1
No two electrons in an atom can have the same quantum numbers.
The actual yield divided by the theoretical yield, times 100.
A row (left to right) in the periodic table.
The properties of elements change with increasing atomic number
in a periodic way. That's why you can stick the elements
into a big chart and have the elements line up in nice families.
A chart which shows how the phase depends on various conditions
of temperature and pressure.
The state of a compound (solid, liquid, or gas)
A property which can be determined
without changing something chemically. If that doesn't make
sense, see the definition of "chemical change".
A double bond.
A covalent bond where one atom tries to grab the electrons from
the other one. This occurs because the electronegativities
of the two atoms aren't the same.
contains more than one atom.
A molecule containing many repeating units. Plastics are
polymers and are formed by free radical chain reactions.
An acid that can give up more than one hydronium ion.
Examples are sulfuric acid and phosphoric acid.
The energy something has because of where it is. Things
that are way up high have more potential energy than things that
are way down low because they have farther to fall.
A measurement of how repeatable a measurement is. The more
significant figures, the more precise the measurement.
The thing you make in a chemical reaction.
The branch of physical chemistry that describes how energy can
only exist at certain levels and makes generalizations about how
atoms behave from this assumption.
When a substance has an unstable nucleus that can fall apart,
it's referred to as radioactive.
The vapor pressure of a solution is directly proportional to the
mole fraction of the solvent.
The slowest step in a chemical reaction.
A mathematical expression for the speed of a reaction as a
function of concentration. A hint: It's usually true
that things go faster if you have more stuff in the first place.
A reaction that has both an oxidation and reduction.
When more than one valid Lewis structure can be drawn for a
molecule, these structures are said to be resonance structures.
Resonance structures arise from the fact that the electrons are
A reaction in which the products can make reagents, as well as
the reagents making products.
mean square velocity
The square root of the average of the squares of the individual
velocities of the gas particles in a mixture. To put it in
a way that a normal human can understand, it's the average of how
fast the particles in a gas are going (assuming you ignore the
direction they're traveling in).
An ionic compound.
When the maximum amount of solute is dissolved in a liquid
law of thermodynamics:
Whenever you do something, the universe gets more random.
A substance that conducts electricity poorly at room temperature,
but has increasing conductivity at higher temperatures.
Metalloids are usually good semiconductors.
The outer electrons aren't pulled very tightly by the nucleus
because the inner electrons repel them. This repulsion is
called the shielding effect, and can be used to explain lots of
bond: A real
fancy way of saying "single bond"
The number of digits in a number that tell you useful
information. For example, when you weigh yourself on a
bathroom scale, it says something like 150 pounds rather than
150.32843737 pounds. Why? Because the thing can only
weigh accurately to the nearest pound. Any other digits
that are on this number don't mean anything, because they're
probably wrong anyway.
reaction (a.k.a. single
When one unbonded element replaces an element in a chemical
compound. These are frequently redox reactions.
A measurement of how much of a solute can dissolve in a liquid.
this value indicates the degree to which a compound dissociates
in water. The higher the solubility product constant, the
more soluble the compound.
The solid that gets dissolved in a solution.
The liquid that dissolves the solid in a solution.
The amount of heat required to increase the temperature of one
gram of a substance by one degree.
The ions in a reaction that don't react.
A change that occurs by itself. All exothermic reactions
are spontaneous. However, this doesn't mean that all
exothermic reactions are fast. The combustion of gasoline
is spontaneous, but not very fast unless you add a little
atmosphere and 273 K.
This is the idea that the functional groups on big molecules get
in the way of a chemical reaction, making it go slower.
Imagine a fat guy trying to get into a Honda Prelude - that's
The art of figuring how much stuff you'll make in a chemical
reaction from the amount of each reagent you start with.
See standard temperature and pressure.
acid: An acid
that fully dissociates in water
The force that holds the nucleus together. As the name
suggests, this force is strong.
See Lewis structure.
When a solid can change directly into a gas. Dry ice does
When you cool something below its normal freezing point
When more solute is dissolved in a liquid than is theoretically
possible. This doesn't happen much, as you might imagine.
A measurement of how much the molecules on a liquid tend to like
to stick to each other. If something has a high surface
tension, it likes to bead up.
A mixture that looks homogeneous when you stir it, but where the
solids settle out when you stop. Mud is a very short-lived
suspension, while peanut butter is a very long-lived suspension.
When you make a big molecule from two or more smaller ones.
Everything you're talking about at the moment.
A measurement of the average kinetic energy of the particles in a
The amount of product which should be made in a chemical reaction
if everything goes perfectly.
The study of energy
law o' thermodynamics:
The randomness of a system at 0 K is zero.
When the concentration of an acid or base is determined by
The temperature and pressure at which all three states of a
substance can exist in equilibrium.
The simplest part of a crystal that can be repeated over and over
to make the whole thing.
When you haven't yet dissolved all of the solute that's possible
to dissolve in a liquid.
two electrons that aren't involved in chemical bonding.
Also frequently referred to as a "lone pair".
The outermost electrons in an atom.
The pressure of a substance that's present above it's liquid.
For example, you can tell that ammonia has a high vapor pressure
because the smell of it is very strong above liquid ammonia.
When you boil a liquid.
A substance with a high vapor pressure.
A theory for predicting molecular shapes that assumes that
electrons like to be as far from each other as possible.