Glossary of Terms

• Indicators

  Indicators are substances that have colors that are pH dependent. In a titration, they are usually added to the solution in small quantity to detect the endpoint of the titration.

  One commonly used indicator is phenolphthalein, which is colorless in acidic and neutral solutions, but pink in basic solutions.

• Ionic bond

  A bond that is formed by the transfer of electrons from one atom to another. As a result, the positively charged ion is attracted to the negatively charged ion by coulombic attraction.

  The strong attractions within ionic solids are responsible for their high melting points. For example, the melting point of the ionic compound sodium chloride, NaCl, is 801 ^oC.

  Ionic bonded solids such as NaCl do not conduct electricity. This is because the electrons in an ionic compound do not move through the ionic structure like that in metallic bonding.

  The smallest unit in ionic compounds is a formula unit as ionic compounds do not exist as discrete entity but as ions.

• Ionization

  Some covalent compounds dissolves in water to produce ions in aqueous solution. When the covalent bond is broken, a cation and an anion is produced.

• Ions

  Ions are electrically charged species. They are formed when a neutral atom either gains or lose electrons. An ion is negatively charged if the atom gains electron(s). It is positively charged if the atom loses electron(s).
  (Note: Ions can also be formed by a group of atoms either gains or loses electrons.)

• Isoelectronic

  Species that have the same number of electrons. For example, Na⁺ and Ne are isoelectronic.

• Isotope

  Isotopes of an element are atoms having the same atomic number but different numbers of neutrons in their nuclei. Therefore, they have different masses.
  For example, ¹²C has 6 neutrons, ¹³C has 7 neutrons.

• Joule

  The SI unit of energy.

  1 joule = 1 kg m2s-2 = 4.184 cal

• The Kelvin scale

  The lowest possible temperature on the Kelvin scale is 0 K, where

  K = oC + 273.15

  Therefore, absolute zero is -273.15 ^oC.

• Kinetic energy

  This is energy of motion. It depends on the object's mass and velocity. The mathematical equation that relates kinetic energy to mass and velocity is

  K.E. = ½mv2

• Law of Conservation of Energy

  states that energy can be neither created nor destroyed. It can only be changed from one form to another (ie - from kinetic energy to potential energy or vice versa).

• Law of Conservation of Mass

  states that mass is neither created nor destroyed, therefore, atoms are neither created nor destroyed.

• Gilbert N. Lewis

  (1875-1946). Lewis made numerous outstanding contributions to chemistry. Students learning chemistry remember him by his contribution in making the concept of valence electrons easier to understand by using the electron-dot symbols to represent valence electrons as dots.

• Lewis electron-dot symbol

  The symbol of an element surrounded by one to eight dots to represent the valence electrons of an atom or ion of the element.

• Litmus Paper

  Litmus is an indicator. Litmus paper is an indicator paper that is used to distinguish between acids and bases.

• Mass number

  The total number of protons and neutrons in the nucleus of an atom is the mass number.It is also the atomic mass of the atom rounded to the nearest whole number.
  For example,

  Element	Mass number
  Carbon (atomic mass = 12.011 amu)	12
  Copper (atomic mass = 63.546 amu)	64

• Matter

  Matter is any object or material that occupies space. The quantity of matter is measured by its mass. All the materials we see around us are examples of matter.

• Melting point

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

• Metallic bond

  This is bonding of metal atoms where positive metal ions are in a three-dimensional arrangement and the valence electrons are able to move freely over the entire structure of the metal. Thus metals can conduct electricity. This type of bonding is different from ionic bonding and covalent bonding.

• Metalloids

  See semimetals.

• Metals

  Metals generally have the following properties:
  • high luster,
  • conduct electricity,
  • conduct heat,
  • malleable, and ductile,and
  • high densities.

  It is the group of elements that are to the left of the diagonal line on the periodic table.

• Mixture

  Any sample of matter that is not an element or compound. It is any matter consisting of two or more substances physically combined. The composition of a mixture, unlike that of a substance, has no particular proportion.

• Molar Mass

  The mass, in grams, of one mole of any substance. For example,

  Substance	Molar Mass
  carbon	12.011 g/mole
  H2 (g)	2.016 g/mole

• Molar Volume

  The volume of one mole of gas at STP is 22.4 liter/mole.

• Mole

  A mole is a counting unit, much like counting by a dozen. A dozen items equal 12 items. A mole items equal Avogadro's number , N_A , or 6.02214 x 10²³ items. It is used to count microscopic particles.

  One mole of an element is NA atoms.

  One mole of a compound is NA molecules.

• Molecule

  A compound formed by two or more atoms joined together by covalent bonds.

• Molecular formula

  The chemical formula that gives the actual number of atoms of each kind present in a molecule of the substance.

• Molecular mass

  The sum of the atomic masses of all atoms in one molecule of a compound.

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

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All contents copyrighted © 1996
Rosamaría Fong, Instructor of Chemistry
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