Fundamental ideas

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States of matter

Solids - fixed shape and volume & cannot be compressed. 

solids

Liquids - have a fixed volume, but they can flow and change their shape

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Gasses - have no fixed shape or volume

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Changing state

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Energy changes during changes of state

  • When melting or boiling, the energy we provide in heating the solid is being absorbed to break the forces between the particles in the solid
  • When freezing or condensing, energy is released to the surroundings as stronger forces form between particles
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Evidence for particles

  • Diffusion in liquids:

Potassium manganate crystals (KMnO4) in water 

  • Diffusionn in gasses:

Bromine (Br2) liquid is placed in a glass jar with a lid & the vapour evaporates from the volatile liquid and fills the gas jar. Then a second gas jar of air is placed upside down on top of the original bromine filled gas jar and the lid is removed. The bromine gas gets distributed evenly between the two gas jars after some time. Diffusion takes place faster in a gas than a liquid.

  • Diffusion thorugh a gas

Cotton wool soaked in ammonia (NH3) is placed at one end of a tube and cotton wool soaked in hydrogen chloride (HCl) is placed at the other. HCl and NH3 molecules diffuse through the air towards eachother & react to form a white powder called ammonium chloride (NH4Cl) when they meet.

HCl(g)          +         NH3(g)     (http://www.gcsescience.com/reversible-arrow.gif)           NH4Cl(s)

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Atoms

  • Substances made up of only one type of atom are called elements
  • Atoms of each element are represented by a chemical symbol
  • There are about 100 different elements
  • Elements are shown in the periodic table
  • The groups contain elements with similar properties
  • Substances made up of different types of atom joined together are called compounds. Chemical bonds hold the atoms tightly together in compounds
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Atomic structure

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  • Proton: +1 charge & relative mass 1
  • Neutron: 0 charge & relative mass 1
  • Electron: -1 charge & relative mass very small
  • Every atom contains equal numbers of protons and electrions so the positive and negative charges cancel out and its charge is zero
  • The number of protons in each atom of an element is its atomic number
  • The sum of the protons and neutrons in an atom is its mass number
  • Atoms of the same element can have different numbers of neutrons - these atoms are called isotopes of that element
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Electrons and the periodic table

  • The chemical properties of an element depend on how many electrons it has
  • The way an element reacts is determined by the number of electrons in its highest energy level (or outermost shell)
  • Atoms in the same group have the same number of electrons in their highest energy level so they all react in a similar way

                                                   Group: 1 2 3 4 5 6 7 8 

No. of electrons in outer shell: 1 2 3 4 5 6 7 8

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