Chemistry Reference

Glossary
absolute zero - at -273.15 degrees Celsius or 0 kelvins, it is the lowest possible temperature in the universe. Although it can never be achieved, measurements within fractions of a kelvin have been made. Particles would attain a minimum amount of energy (and motion) at absolute zero.
acid (Arrhenius) - a compound that dissociates in water to produce H+ ions. HCl is an Arrhenius acid because it dissociates into H+ and Cl- ions.
alpha particle - a helium nucleus; a radioactive particle made of two protons and two neutrons. Alpha particles are not able to penetrate matter easily due to their large size.
acceleration - is a change in velocity (speed and direction) over a measured length of time. The ball rolling down the hill accelerated from rest to a fast speed in a matter of seconds.
alkali earth metal - a group two element. The alkali earth metals are found in minerals within the earth's crust.
alkali metal - a group one element, with the exception of hydrogen. The alkali metals are extremely reactive with water.
alkane - an organic molecule that only contains single bonds between carbon atoms. The names of alkanes such as propane and hexane end in the suffix -ane.
amorphous - describes a solid that does not have a crystalline structure. The particles in window glass or wax do not have a regular, repeating pattern so they are amorphous solids.
anion - a negatively charged particle. Chlorine gains an electron to make an anion with a -1 charge.
aqueous - soluble in water. Unlike oil, sugar and salt can make aqueous solutions.
atomic radius - the distance from the nucleus to the edge of the electron cloud of an atom. Due to the ambiguity involved in determining the edge of the electron cloud, the atomic radius is often determined by halving the distance between two contiguous atoms of the same element.
base (Arrhenius) - a compound that dissociates in water to produce OH- (hydroxide) ions. KOH is an Arrhenius base because it dissociates into K+ and OH- ions.
cation - a positively charged particle. Potassium loses an electron to make an cation with a +1 charge.
chalcogen - a group 16 element. Chalcogens have six valence electrons because their electron configurations end in s2p4.
chemical formula - sometimes called the molecular formula, it tells how many atoms of each element are present in a molecule of a particular compound. According to the chemical formula of water, H2O, there are two hydrogen atoms and one oxygen atom in each water molecule.
combustion - a chemical reaction where a hydrocarbon or organic compound reacts with oxygen in the presence of heat to produce either carbon dioxide, carbon monoxide, or carbon and water vapor. The combustion of fuels produces water, but you cannot see it since it is a gas.
covalent bond - when two elements of similar or the same electronegativty share electrons by forming a hybrid orbital. Carbon and hydrogen, two nonmetals, form a covalent bond to share electrons in an sp hybrid orbital.
current - in electricity, it refers to a flow of charge, usually through a metallic wire or via electrolytes in aqueous solution. Electric current often describes the flow of electrons in a copper wire.
density - is the ratio of mass to volume for a given substance. The density of aluminum is 2.70 g/mL.
dissociation - occurs when water molecules separate an ionic compound as it dissolves in water. The process takes place when the anion of the solute is attracted to the hydrogens in the water molecule and the cation of the solute is attracted to the oxygen in the water molecule. When potassium chloride dissociates in water, the potassium ion is attracted to the oxygen of the water molecule and the chloride is attracted to the hydrogens.
ductility - a physical property typically associated with metals that refers to a substance's ability to be drawn into a wire. Copper is used to make wire because it is ductile.
fission - in nuclear reactions, the term refers to the splitting of a nucleus (usually of large mass) into smaller nuclei, free neutrons, and energy. The fission of uranium-235 yields the smaller nuclei or barium and krypton and three neutrons.
fusion - in nuclear reactions, the term refers to the joining (fusing) of small nuclei into a larger nucleus, accompanied by the release of energy.  Fusion reactions are not easily reproducible on Earth due to the extreme temperatures required, yet it is the reaction that powers the sun and stars of the universe.
gas - the state of matter with greatest separation between particles, and thus the most entropy. They have an indefinite shape and volume. The particles in a gas are spread so far apart that the majority of the volume is empty space.
group - in chemistry, refers to the vertical columns of the periodic table. There are 18 groups, or families, stretching from left to right on the periodic table.
half-life - the time it takes for one-half of a radioactive isotope to undergo decay. A radioactive isotope that has a half-life of 6 hours and a mass of 10 g, will only have 2.5 g remaining after 12 hours.
halogen - a group 17 element. The halogens are extremely reactive since they only need one electron to attain an octet.
heterogeneous mixture - contains two or more unique substances that can be visually identified from one another. The different components can be separated easily. A salad is a heterogeneous mixture since the lettuce, tomatoes, and dressing are all very easy to identify as unique components.
homogeneous mixture - contains two or more unique substances than appear to be one uniform substance. It is not possible to see the different components visually. Solutions such as seawater are homogeneous mixtures because you differentiate between the salts and the water.
ion - a particle with unequal numbers of protons and electrons. A sodium ion has 11 protons and 10 electrons.
ionic bond - is formed when one element of low electronegativity gives electron(s) to an element of high electronegativity. They are also formed by the positive/negative attraction between polyatomic cations/metals and polyatomic anions/nonmetals. Since there is a large difference between the electronegativity of strontium and chlorine, strontium will give electrons to chlorine and form an ionic bond.
(nth) ionization energy - the energy needed to remove "n" electrons from an atom. The second ionization energy for magnesium is the energy needed to remove two electrons from a magnesium atom.
isotope - refers to one of many different variations in the number of neutrons (and therefore mass) within atoms of a given element. Two isotopes of carbon, carbon-12 and carbon-14 both have six protons, but carbon-12 atoms have six neutrons while carbon-14 atoms have eight neutrons.
Lewis dot diagram - is a graphical representation of the number of valence electrons for an element. Lewis dot diagrams are not useful for transition elements since they use electrons outside their valence for bonding.
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