Chemistry Topic 1

• atom


  the smallest unit of matter

  
• element


  a substance made of only 1 type of atom
• compound


  a substance made of at least two different types of atom chemically bonded together
• mixture


  two or more substances that are mixed together but are not joined by bonds
• chemical symbol


  the letters on the periodic table that give the name of each element, every element has its own chemical symbol
• chemical formula


  the collection of chemical symbols that show how many of each element are present in a molecule or compound
• nucleus


  the centre part of an atom that contains the protons and neutrons
• proton


  sub-atomic particle that makes up the nucleus of an atom, has a mass of 1 and a charge of +1
• neutron


  sub-atomic particle that makes up the nucleus of an atom, has a mass of 1 and a charge of 0
• electron


  sub-atomic particle found orbiting the nucleus in an electron shell, has a mass of almost 0 and a charge of -1
• ion


  an atom that has lost or gained electrons to become charged, lost electrons leave a positive ion, gained electrons leave a negative ion
• conservation of mass


  a rule that says you must have the same amount of atoms at the end of a chemical reaction as you started with
• chemical equation


  a way of showing what happens in a chemical reaction using the chemical symbols and formulae of the substances
• balanced equation


  a chemical equation written so that there are the same number of each type of atom on each side of the equation
• atomic number


  the smaller number next to the chemical symbol that identifies an element and gives the number of protons and electrons in that atom
• mass number


  the larger number next to the chemical symbol of an element that measures the mass of the atom (Mass number = number of protons + number of neutrons)
• electron shell


  one of the regions outside of the nucleus where electrons can be found
• electronic structure


  a diagram showing how the electrons are arranged in the electron shells (the 1st shell can have a maximum of 2 electrons, the others can hold up to 8 electrons)
• filtration


  a technique used to separate an insoluble substance from a solvent (one that does not dissolve)

  
• crystallisation

  a technique used to separate a soluble solid (or salt) from a solution

  
• distillation


  a technique used to obtain the solvent (or liquid) from a solution

  
• fractional distillation


  a technique used to separate two liquids (ones that do mix together)

  
• chromatography

  a technique commonly used to separate a mixture of dyes in ink

  
• J.J. Thomson

  the scientist who discovered the electron and proposed the plum pudding model
• plum pudding model


  a model of the atom that proposed the nucleus was a ball of positive charge with negative electrons embedded in it (we now know this is incorrect)

  
• Rutherford's experiment


  the experiment that proved the nucleus must be positively charged (as alpha particles were scattered/deflected by a piece of gold foil)

  
• Niels Bohr


  the scientist who proposed that electrons are found in shells, and orbit at fixed distances
• James Chadwick

  the man who proposed the existence of neutrons
• isotope


  atoms of the same elements with the same atomic number but different mass numbers (different numbers of neutrons in the nucleus)