Glossary of Terms

• Density

  The density of a substance is a physical property of the substance. It is the mass of a substance occupying a certain volume. The unit of density is usually expressed as the mass divided by the volume.
  
  • g/mL
  • g/cc
  • g/L

• Diatomic elements

  The seven elements that exist as diatomic molecules.

  The diatomic elements
  H, N, O, F, Cl, Br, and I

• Diatomic molecules

  Molecules that are composed of two atoms.

• Dipole moment

  The dipole moment is a measure of the extent to which a separation of charge exists within a molecule.

• Dissociation

  The process by which ionic compounds break up into their individual ions in the presence of water molecules.

• Electrolyte

  These are substances that produce ions in aqueous solution. It is also a solution that conduct an electric current.
  Ionic compounds and strong acids and bases are strong electrolytes.

• Electronegativity

  is a measure of the tendency of an atom to attract electrons to itself in a covalent bond.

• Electrons

  Electrons are negatively charged fundamental particles. They are found outside the nuclei of all atoms. The mass of an electron is 1/1835 of the mass of a proton.

• Element

  A substance in which all the atoms have the same atomic number. It is a substance that cannot be broken down into simpler substances.

• Empirical formula

  Also known as the simplest formula. It is the chemical formula that gives the simplest whole-number ratio of atoms of each element in a compound. In some compounds the empirical formula is the same as the molecular formula . For example,
  • For water, H₂O is the molecular formula. H₂O is also the empirical formula because the ratio of H to O in the molecular formula is also the simplest whole-number ratio.
  • For benzene, C₆H₆ is the molecular formula. The empirical formula is CH, the simplest ratio of C to H.

• Empirical formula unit

  In benzene, the molecular formula is C₆H₆. The empirical formula is CH. Therefore, there are six empirical formula units in benzene.

  (Molar mass of compound) / (Mass of the Empirical formula) = Number of Empirical Formula Units

• Energy

  When samples of matter react chemically, energy is almost always absorbed or released. So, the study of energy is an integral part of the study of chemistry.

• Fahrenheit

  A temperature scale based on a value of 32 ^oF as the melting point of ice and 212^oF as the boiling point of water.

  oF = {(9/5) oC} + 32

• Family of elements

  See group of elements.

• Formula mass

  The formula weight of a substance is the sum of the atomic masses of all atoms in a formula unit of the substance expressed in amu.

• Formula unit

  The smallest unit of an ionically bonded substance. For example, the formula unit of sodium chloride is NaCl.

• Ground state

  The ground state of the electrons in an atom is the energy associated with the arrangement of the electrons such that they are at the lowest possible energy level. Because electrons are constant moving, the ground state energy is not zero.

• Group of elements

  A vertical column of elements in the periodic table.

• Halogens

  All the elements in Group VIIA of the periodic table.

• Heterogeneous mixture

  Heterogeneous mixtures do not have the same composition and properties throughout a sample. Some examples of heterogeneous mixtures are: iced tea, blood, milk.

• Homogeneous mixture

  Homogeneous mixtures are called solutions. Homogeneous mixtures have the same composition and properties that are uniform throughout a sample, but different samples may have different properties. A homogeneous mixture can be separated into its components by appropriate physical changes. Some examples of solutions are: gasoline, seawater, tea.

Rosamaría Fong, Instructor of Chemistry,
British Columbia Institute of Technology, Burnaby, B.C. Canada.

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Rosamaría Fong, Instructor of Chemistry
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