Chemistry Definitions

Chemistry Definitions

1. Atoms, molecules and ions

   • Particle
     • A minute portion of matter
   • Atom
     • The smallest particle of an atom which shows the properties of that element
   • molecule
     • Two or more atoms joined together by covalent bonds (sharing electrons). They have no electrical charge
   • Ion
     • An atom or molecule that is electrically charged because it has either gained or lost electrons
   • Ca+ion
     • A positive ion (electrons missing)
   • Anion
     • A negative ion (extra electrons)
   • Isotopes
     • Atoms of the same element which have the same atomic number but with different mass numbers. They have identical chemical properties because they have exactly the same electron configuration
   • Atomic number
     • The number of protons in the nucleus of atom
   • Mass number
     • The total number of protons plus neutrons in the nucleus of an atom
   • Relative Formula Mass
     • The average mass of a molecule. it is the sum of all the individual relative atomic masses
   • Relative Atomic Mass
     • The average mass of an atom (a weighted average that takes into account the mass numbers and abundances of all the stable isotopes of the element
   • Diffusion
     • The spreading out and mixing of particles

2. Symbols, Formulae and Equations

   • Empirical Formula
     • The simplest (whole number) ratio of atoms of each element in a compound
   • Molecular Formula
     • The actual number of atoms of each element in a molecule of the compound
   • Electrode(ionic/ half) equation
     • These equations use ion formulae with charges and electrons to represent the gain or loss of electrons at the electrodes in electrolysis

3. Structure and Bonding

   • Structure
     • There are two types of structure: Giant lattice (a very large number or atoms or ions forming one huge crystal) or Simple Molecular
   • Metallic Bonding
     • A giant lattice of close-packed metal ions (+ve) surrounded by a “sea” of delocalised valence (outer) electrons. Electrostatic attraction of the cations for the negatively charged “sea” of electrons is strong.
   • Ionic Bonding
     • Ionic compounds are formed between metals and non-metals and they form giant lattices. The strong electrostatic force of attraction between +ve and –ve ions is called ionic bonding.
   • Covalent Bond
     • A pair of electrons shared between two atoms. Simple molecules have one or more covalent bonds in them. There are a few giant covalent lattices, most importantly diamond and graphite.
   • Allotropes
     • Different structural forms of the same element, in particular you need to know about diamond and graphite as allotropes of carbon.