C1 Atomic Structure


C1.1: Atoms

  • all substances are made up of atoms 
  • the periodic table lists all the chemical elements with 8 main groups containing elements with similar chemical properties. 
  • elements only contain one type of atom
  • compounds contain more than one type of atom.
  • an atom has a tiny nucleus at its centre, surrounded by electrons. 
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C1.2: Chemical equations

  • no new atoms are ever created or destroyed in a chemical reaction.
  • total mass of reactants = total mass of products
  • there is the same number of each type of atom on each side of a balanced symbol equation
  • you can include state symbols to include extra information in balanced symbol equations:
    • (s) = solid
    • (l) = liquid
    • (g) = gas
    • (aq) = aqueous solution
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C1.3: Separating mixtures

  • a mixture is made up of two or more substanced that are not chemically combined together.
  • mixtures can be separated by physical means:
  • filtration
  • crystallisation
  • simple distillation
  • fractional distillation
  • chromatography
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C1.4: Fractional Distillation and Paper Chromatogr

  • fractional distillation is an effective way of separating miscible liquids using a fractionating column. 
  • the separation is possible as the liquids in the mixture have different boiling points. 
  • paper chromatography separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper.
  • the different substances are separated because of their different solubilities in the solvent used. 
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C1.5: History of the Atom

  • ideas about atoms have changed over time
  • new evidence has been gathered from the experiments of scientists who have used their model of the atom to explain their observations, calculations and discoveries.
  • key ideas have been proposed successfully by:
    • Dalton - little, hard spheres; cannot be divided or split; building blocks of nature
    • Thompson - discovery of the electron; 2000x smaller than lightest atom
    • Rutherford - positive charge concentrated; electrons must orbit; protons are positive 
    • Bohr - electrons must orbit nucleus at set distances; high to low energy level
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C1.6: Structure of the Atom

  • atoms are made of protons, neutrons and electrons
  • protons = +1 charge; relative mass = 1
  • neutrons = 0 (neutral) charge; relative mass = 1
  • electrons = -1 charge; relative mass = 1/2000
  • atoms contain equal numbers of protons and electrons, producing a neutral charge overall.
  • atomic number = number of protons
  • mass number = number of protons and neutrons
  • atoms of the same element hae the same number of protons and electrons in their atoms. 
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C1.7: Ions, Atoms and Isotopes

  • atoms that gain electrons form negative ions. if they lose electrons they form positive ions.
  • isotopes are atoms of the same element with different numbers of neutrons.
  • an isotope's chemical properties are identical but it may have different physical properties, such as density. 
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C1.8: Electronic Structures

  • the electrons in an atom are arranged in energy shells
  • the lowest energy level - the first shell - can hold up to 2 electrons, the next can hold up to 8 electrons. 
  • the next shell only begins to fill when the one below is full.
  • the number of electrons in the outermost shell of an element's atoms determines the way in which that element reacts. 
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