Fundamental Ideas


Atoms, Elements & Compounds

Element: Contains only one type of atom

Compound: Two or more elements chemically joined together


  • All living things are made up of atoms
  • They are the smallest part of an object
  • An atom is made up of a nucleus with electrons, protons and neutrons around it
  • Protons and electrons have opposite charges ( +ve and -ve), while Neutrons are neutral
  • Atoms are neutral (have the same number of protons and electrons)
  • Atomic number = no. of electrons/ protons
  • Mass number =  no. of protons + neutrons
  • Elements (atoms) are arranged on the periodic table in order of their atomic number
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Atoms & Energy Shells

Energy Shells:

  • Electrons are arranged in energy 'shells'.
  • A shell can only hold so many electrons- the first shell holds 2 electrons, the second, third, fourth etc. can hold up to 8.
  • After one shell is filled, the remaining electrons fill the next no. shell
  • Atoms with the same number of electrons on their outer shell are in the same 'group' on the periodic table
  • The number of electrons on the outer shell determines the way that the element reacts
  • Atoms in Group 0 (noble gases) are stable
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Compounds & Atoms bonding

Atoms making compounds:

  • When different elements react together, they form chemical bonds to make compounds
  • Making bonds means that some electrons are taken away, given or shared
  • When metals react with non-metals, charged particles IONS are formed
  • The properties of the compound are different from the elements
  • The total mass of reactants = the total mass of products

Ionic Bonding:

  • Metal atoms lose electrons to form positive ions
  • Non-metal atoms gain electrons to form negative ions
  • The opposite charges mean they're strongly attracted to one another

Covalent Bonding:

  • Each atom shares an electron with another atom
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