Chemistry Vocabulary

One of the things that chemistry students at all levels have problems with is vocabulary.  Unfortunately, many chemistry books and teachers like to talk in great big words rather than saying what they mean in common English.  Why?  Because they were forced to talk like this when they were students and they feel it's The Right Thing To Do.  Maybe it is.  Who am I to say it's wrong?  Wait a minute... it's my website and I can say whatever I want.  It's wrong to talk like that.

In any case, if you're reading a book or your teacher is making you use the big words, it doesn't do much good to go up to him/her/it and say "Mr. Guch says it's wrong to use big words."  For one thing, it'll make both of us look like morons.  For another thing, it won't make anybody speak nicer.  As a result, you're just going to have to get used to it.  I have, however, included a list of vocabulary words below that chemistry students commonly have problems with.

If you're a college student or grad student looking for a vocabulary list with more involved terms on it, click HERE to see my Even Bigger Vocabulary List. If you just don't feel like seeing vocabulary words right now, head back to my main website by clicking HERE.
 

Mr. Guch's Great Big Vocabulary List

Due to my recent work to update this site, some of the terms in the vocabulary list have been improved and expanded on the new version of this site. As a result, words starting with letters A-D and those starting with E-H are on new pages. However, if you want to see the other terms, just scroll down for a second (though they'll soon be replaced with new awesomeness, too!)

Terms starting with A-D

Terms starting with E-H

Terms starting with I-L


  • main-block elements:  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.

  • mass defect:  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 energy")

  • mass:  The amount of matter in an object.  The more mass, the more stuff is present.

  • mechanism:  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.

  • molality:  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.

  • molar mass:  The mass of one mole of particles. 

  • molar volume:  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 gas.

  • molarity:  A unit of concentration equal to moles of solute divided by liters of solution.

  • mole fraction:  The number of moles of stuff in a mixture that are due to one of the compouds. 

  • mole ratio:  The ratio of moles of what you've been given in a reaction to what you want to find.  Handy in stoichiometry.

  • mole:  6.02 x 1023 things.

  • molecular compound:  A compound held together by covalent bonds.

  • molecular formula:  A formula that shows the correct quantity of all of the atoms in a molecule.

  • monatomic ion:  An ion that has only one atom, like the chloride ion.

  • neutralization reaction:  The reaction of an acid with a base to form water and a salt.

  • node:  A location in an orbital where there's no probability of finding an electron.

  • nonpolar covalent bond:  A covalent bond where the electrons are shared equally between the two atoms.

  • normal boiling point:  The boiling point of a substance at 1.00 atm.

  • normal melting point:  The melting point of a substance at 1.00 atm.

  • normality:  The number of equivalents of a substance dissolved in a liter of solution.

  • nuclar fusion:  When many small atoms combine to form a large one.  This occurs during a thermonuclear reaction.

  • nuclear fission:  This is when the nucleus of an atom breaks into many parts.

  • nuclear reaction:  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 lab.

  • nucleon:  A particle (such as proton or neutron) that's in the nucleus of an atom.

  • octet rule:  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 compounds).

  • optical isomerism:  Isomerism in which the isomers cause plane polarized light to rotate in different directions.

  • orbital:  This is where the electrons in an atom live.

  • organic compound:  A compound that contains carbon (except carbon dioxide, carbon monoxide, and carbonates)

  • osmosis:  The flow of a pure liquid into an area of high concentration through a semi-permeable membrane.

  • oxidation number:  The apparent charge on an atom.

  • oxidation:  When a substance loses electrons.

  • partial pressure:  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 atm.

  • Pauli exclusion principle:  No two electrons in an atom can have the same quantum numbers.

  • percent yield:  The actual yield divided by the theoretical yield, times 100.

  • period:  A row (left to right) in the periodic table.

  • periodic law:  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.

  • pH:  -log[H+]

  • phase diagram:  A chart which shows how the phase depends on various conditions of temperature and pressure.

  • phase:  The state of a compound (solid, liquid, or gas)

  • physical property:  A property which can be determined without changing something chemically.  If that doesn't make sense, see the definition of "chemical change".

  • pi-bond:  A double bond.

  • polar covalent 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.

  • polyatomic:  contains more than one atom.

  • polymer:  A molecule containing many repeating units.  Plastics are polymers and are formed by free radical chain reactions.

  • polyprotic acid:  An acid that can give up more than one hydronium ion.  Examples are sulfuric acid and phosphoric acid.

  • potential energy:  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.

  • precision:  A measurement of how repeatable a measurement is.  The more significant figures, the more precise the measurement.

  • pressure:  Force/area

  • product:  The thing you make in a chemical reaction.

  • quantum theory:  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.

  • radioactive:  When a substance has an unstable nucleus that can fall apart, it's referred to as radioactive.

  • Raoult's Law:  The vapor pressure of a solution is directly proportional to the mole fraction of the solvent.

  • rate determining step:  The slowest step in a chemical reaction.

  • rate law:  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.

  • redox reaction:  A reaction that has both an oxidation and reduction.

  • resonance structure:  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 delocalized.

  • reversible reaction:  A reaction in which the products can make reagents, as well as the reagents making products.

  • root mean square velocity (RMS 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).

  • salt:  An ionic compound.

  • saturated:  When the maximum amount of solute is dissolved in a liquid

  • Second law of thermodynamics:  Whenever you do something, the universe gets more random.

  • semiconductor:  A substance that conducts electricity poorly at room temperature, but has increasing conductivity at higher temperatures.  Metalloids are usually good semiconductors.

  • shielding effect:  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 neat-o stuff.

  • sigma bond:  A real fancy way of saying "single bond"

  • significant figure:  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.

  • single-displacement reaction (a.k.a. single replacement reaction):  When one unbonded element replaces an element in a chemical compound.  These are frequently redox reactions.

  • solubility:  A measurement of how much of a solute can dissolve in a liquid.

  • solubility product constant:  Abbreviated Ksp, this value indicates the degree to which a compound dissociates in water.  The higher the solubility product constant, the more soluble the compound.

  • solute:  The solid that gets dissolved in a solution.

  • solvent:  The liquid that dissolves the solid in a solution.

  • specific heat capacity:  The amount of heat required to increase the temperature of one gram of a substance by one degree.

  • spectator ions:  The ions in a reaction that don't react.

  • spontaneous change:  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 energy. 

  • standard temperature and pressure:  One atmosphere and 273 K.

  • steric hindrance:  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 steric hindrance.

  • stoichiometry:  The art of figuring how much stuff you'll make in a chemical reaction from the amount of each reagent you start with.

  • STP:  See standard temperature and pressure.

  • strong acid:  An acid that fully dissociates in water

  • strong nuclear force:  The force that holds the nucleus together.  As the name suggests, this force is strong.

  • structural formula:  See Lewis structure.

  • sublimation:  When a solid can change directly into a gas.  Dry ice does this.

  • supercooling:  When you cool something below its normal freezing point

  • supersaturated:  When more solute is dissolved in a liquid than is theoretically possible.  This doesn't happen much, as you might imagine.

  • surface tension:  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. 

  • suspension:  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.

  • synthesis:  When you make a big molecule from two or more smaller ones.

  • system:  Everything you're talking about at the moment.

  • temperature:  A measurement of the average kinetic energy of the particles in a system.

  • theoretical yield:  The amount of product which should be made in a chemical reaction if everything goes perfectly.

  • thermodynamics:  The study of energy

  • Third law o' thermodynamics:  The randomness of a system at 0 K is zero.

  • titration:  When the concentration of an acid or base is determined by neutralizing it.

  • transition state:  See "activated complex"

  • triple point:  The temperature and pressure at which all three states of a substance can exist in equilibrium.

  • unit cell:  The simplest part of a crystal that can be repeated over and over to make the whole thing.

  • unsaturated:  When you haven't yet dissolved all of the solute that's possible to dissolve in a liquid.

  • unshared electron pair:  two electrons that aren't involved in chemical bonding.  Also frequently referred to as a "lone pair".

  • valence electron:  The outermost electrons in an atom.

  • vapor pressure:  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. 

  • vaporization:  When you boil a liquid.

  • volatile:  A substance with a high vapor pressure.

  • VSEPR:  A theory for predicting molecular shapes that assumes that electrons like to be as far from each other as possible. 

Questions?  Comments?  Philosophical rants about how vocabulary defines us, rather than the other way around?  Email me at misterguch@chemfiesta.com