Glossary of Terms

• ### Absolute zero

This is the temperature at which molecular motion ceases. It is the lowest theoretical temperature, but scientists in laboratories have never reached this temperature. The closest is reached to within a thousandth of a degree above absolute zero. Absolute zero is determined to be 273.15 degrees below zero on the Celsius scale.

• ### Accuracy

The closeness of a measurement to the true value.

• ### Acids

A substance that produces hydrogen ions (H+) in water.

• ### Acidic solution

An aqueous solution in which
 [H+] > [OH-]

• ### Activity series of metals

The arrangement of metals in order of decreasing activity. Thus, each element in the series displaces any element below it from its salt or acid.

• ### Alkali metals

All the Group IA elements (except hydrogen) in the periodic table.

• ### Alkaline earth metals

All the Group IIA elements in the periodic table.

• ### Angstrom

An angstrom is a unit of length.

 1 angstrom (Å) = 10-10 meter

• ### Anhydrous salt

A salt that has no water of hydration. For example, CuSO4 is the anhydrous salt of CuSO4· 5H2O (copper (II) sulfate pentahydrate).

• ### Anion

A negatively charged ion.

• ### Atom

An electrically neutral particle that is made up of the fundamental particles of matter. An atom is the smallest particle of matter that characterizes an element.

• ### Aqueous solution

A solution obtained by dissolving a compound in a solvent, specifically water. Any other solvent used does not result in an aqueous solution.

• ### Atomic mass

Atomic mass of an element is the mass of the naturally occurring mixture of isotopes of the element. It has the units of:

 amu / atom grams / mole

The formula to calculate atomic mass from isotopic data is:

 atomic mass = (the fraction of isotope 1)(mass of isotope 1) + (the fraction of isotope 2)(mass of isotope 2) + (the fraction of isotope 3)(mass of isotope 3) + ...

• ### Atomic Mass Unit (amu)

An atomic mass unit is used to express the masses of individual atoms. It is defined as 1/12 of the mass of a carbon-12 (12C) atom.

 1 amu = 1.67 x 10-24 g

• ### Atomic number

Atomic number is the number of protons in the nucleus of the atom. For an electrically neutral atom, this is also the number of electrons outside the nucleus.

• ### Atomic orbitals

An atomic orbital describes the electron charge density or the probability of finding an electron in an atom. The several kinds of orbitals (s, p, d, f, ...)differ in the shapes of the electron clouds they describe.

• ### Avogadro's number

The number of particles in exactly 12 grams of 12C is 6.022137 x 1023, or 1 mole.

• ### Bases

Any substance that releases hydroxide (OH-) ions when dissolved in water.

• ### Niels Bohr

In 1913, a Danish physicist (1885-1962), Niels Bohr, proposed that, based on the model of the hydrogen atom, electons in an atom have their energies restricted to certain values, or specific energy levels.

• ### Boiling point

The temperature at which a substance undergoes a phase transition from a liquid to a gas.

• ### Calorie

The calorie is the quantity of heat required to change the temperature of one gram of water by one degree Celsius.

• ### Cation

An ion with a positive charge.

• ### Celsius

A temperature scale based on a value of 0oC for the melting point of ice and 100oC as the boiling point of water.

 oC = 5/9 (oF - 32)

• ### Characteristic Property

A property that is due to the nature of the material. Examples of characteristic property are:
density, colour, odor, hardness, conductivity ... etc ...

• ### Charge

A fundamental property of electrons (having -1 charge) and protons (having +1 charge). "+1", and "-1" are a relative scale. The actual charge is measured in coulombs.

• ### Chemical change

A chemical change is a chemical reaction in which a sample of matter is transformed into completely different substances.

• ### Chemical Property

Chemical properties describe types of changes a substance can undergo to change into other substances.

• ### Compound

A substance made up of two or more elements in a definite ratio. It can be broken down into its constituent elements by chemical reactions. Compounds must be neutral.

• ### Core electrons

Electrons in the inner shells of the atom are called the core electrons. For example, silicon has 14 electrons. It has 10 core electrons and 4 valence electrons.

• ### Coulombs

The SI unit of electrical charge. The actual charge of a proton is 1.6 x 10-19 coulombs. The actual charge of an electron is - 1.6 x 10-19 coulombs. Since atomic particles have charges which are integral multiples of 1.6 x 10-19 coulombs, it is convenient to use a relative scale based on the actual charge of 1.6 x 10-19 coulombs.

• ### Covalent bond

This type of bonding is usually found between non-metallic elements. In the formation of the covalent bond, electrons are shared between the atoms. As a result, covalent compounds have relatively lower melting points and do not conduct electricity as a solid, liquid or in aqueous solutions.

The smallest unit of a compound formed by covalent bonds is a molecule.