Chemistry Unit 1 key terms

• 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
• 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
• Ionic bond

  Attraction between oppositely charged ions
• Covalent bond


  Formed by a shared pair of electrons
• Diatomic


  Two atoms covalently bonded in a molecule
• Empirical formula

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


  Actual number of atoms of each element in a molecule
• Metallic bonding


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


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


  Can be hammered into shape
• Base


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


  Can be drawn out into wires
• Alkali


  Soluble base
• Alloy

  Mixture of two or more elements at least one of which is a metal and the resulting mixture has metallic properties
• Strong acid


  Ionises completely in water
• Nanometre

  10 to the -9 metres
• Weak acid


  Ionises partially in water
• Nanoparticle


  Structure that is 1 - 100 nm in size
• Strong alkali


  Ionises completely in water
• Weak alkali


  Ionises partially in water
• Allotropes


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


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


  Substance that consists of two or more elements chemically combined
• Atom


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


  Particle that consists 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 the atom compared with that of the carbon-12 isotope, which has a mass of exactly 12, and it is the weighted mean of the mass numbers
• Soluble


  Dissolves in water
• Neutralisation


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


  Compound formed when some or all of the hydrogen ions in an acid are replaced by metal ions or ammonium ions