C1 notes

Atoms and elements


  • contains protons and neutrons
  • protons are positively charged
  • neutrons have no charge
  • the nucleus has a positive charge


  • negatively charged
  • occupy shells around the nucleus
  • atoms have no charge
  • the number of protons always equals the number of electrons
  • if electrons are added or removed, the atom becomes charged and becomes an ion
  • the number of protons decides what type of atom it is
  • if a substance only contains one type of atom it's called an element

The periodic table

  • atoms can be represented by symbols
  • elements with similar properties form columns
  • vertical columns are called groups
  • all of the elements in a group have the same number of electrons in their outer shell
  • the elements in group 0 are the noble gases. This means that they're stable and unreactive. They have eight electrons in their outer shell except helium.

Electron shells

  • electrons always occupy shells
  • the lowest shells are always filled first
  • 1st shell= 2 electrons
  • 2nd shell= 8 electrons
  • 3rd shell= 8 electrons
  • in most atoms the ouer shelll is not full and this makes the atoms want to react to fill it
  • to find the electronic structure of an element, list the number of electrons in each shell


  • when different elements react, atoms form chemical bonds with other atoms to form compunds
  • making bonds involves giving away, taking, or sharing electrons
  • a compound which is formed from a metal and a non metal consists of ions
  • the metal atoms lose electrons to form positive ions and the non metal atoms gain electrons to form negative ions
  • the opposite charges mean they're strongly attracted to each other. This is called ionic bonding
  • a compound formed from non-metals consist of molecules. Each atom shares an electron with another atom- a covalent bond
  • the properties of a compound are totally different from the properties of the original elements

Formulas and reactions

  • a formula shows what atoms are in a compound
  • atoms aren't lost or made in chemical reactions
  • balanced symbol equations show the atoms at the start (the reactants)
  • and the atoms at the end (the products) and how they're arranged
  • the mass of the reactant=the mass of the product

Balancing equations

  • you can balance the equation by putting numbers in front of the formulas where needed
  • find an element that doesn't balance and pencil in a number to try and sort it out
  • see where it gets you. It may create another imbalance-if so, just pencil another number and see where that gets you
  • carry on chasing unbalanced elements and it'll sort itself out pretty quickly

Materials and properties

  • melting point- the temperature where the solid materials turns to liquid
  • strength- how good a material is at resisting a force
  • tensile strength- resisting a pulling force
  • compressive strength- resisting a pushing force
  • stiffness- how good a material is at not bending
  • hardness- how difficult it is to cut into a material

Properties of common materials

  • plastics- hard, strong, stiff, some are low density, some…


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