chem definitions

• Atomic number


  Number of protons in the nucleus of an atom
• Mass number


  Total number of protons and neutrons in the nucleus of an atom
• Isotopes


  Atoms with the same number of protons but different number of neutrons
• Cation


  Positive ion
• Anion


  Negative ion
• Compound


  Substance formed when two or more elements are chemically combined
• Ionic bond


  Attraction between oppositely charged ions
• Covalent bond


  Shared pair of electrons
• Diatomic


  Two atoms covalently bonded in a molecule
• Metallic bonding


  Attraction between delocalised electrons and positive ions in a regular lattice
• Malleable


  Can be hammered into shape
• Ductile


  Can be drawn out into wires
• Alloy


  Mixture of two or more elements, at least one of which is a metal, with metallic properties
• Nanometre


  10^-9 metres
• Nanoparticle


  Structure 1-100 nm in size
• Allotropes


  Different forms of the same element in the same physical state
• Element


  Substance consisting of only one type of atom that cannot be broken down into anything simpler by chemical means
• Compound


  Substance consisting of two or more elements chemically combined
• Atom


  Simplest particle of an element that can exist on its own in a stable state
• Molecule


  Particle consisting of two or more atoms chemically bonded together
• Period


  Horizontal row in the Periodic Table
• Group


  Vertical column in the Periodic Table
• Relative atomic mass


  Mass of an atom compared to carbon-12 isotope with mass of exactly 12
• Water of crystallisation


  Water chemically bonded into the crystal structure
• Hydrated


  Solid crystals contain water of crystallisation
• Dehydration


  Removal of water of crystallisation
• Anhydrous


  Does not contain water of crystallisation
• Degree of hydration


  Number of moles of water of crystallisation chemically bonded in 1 mole of the compound
• Empirical formula


  Simplest whole number ratio of atoms of each element in a compound
• Molecular formula


  Actual number of atoms of each element in a molecule
• Indicator


  Chemical that gives a colour change in acidic, alkaline and neutral solutions
• Base


  Substance that reacts with an acid producing a salt and water
• Alkali


  Soluble base
• Strong acid


  Ionises completely in water
• Weak acid


  Ionises partially in water
• Strong alkali


  Ionises completely in water
• Weak alkali


  Ionises partially in water
• Neutralisation


  Reaction between an acid and an alkali producing a salt and water
• Oxidation


  Is the gain of oxygen, loss of hydrogen or loss of electrons
• Reduction


  Is the loss of oxygen, gain of hydrogen or gain of electrons