C1 - Atomic structure and the periodic table

• All substances are made of atoms
• Atom


  The smallest part of an element that can exist
• Chemical symbol

  Represents atoms of each element, e.g., O for oxygen, Na for sodium
• There are about 100 different elements
• Periodic table

  Shows elements
• Compound

  Formed from elements by chemical reactions
• Chemical reactions always involve the formation of one or more new substances and often involve a detectable energy change
• Compounds

  Contain two or more elements chemically combined in fixed proportions
• Compounds can only be separated into elements by chemical reactions
• Chemical reactions

  Can be represented by word equations or equations using symbols and formulae
• Skills students should be able to demonstrate

  • Use names and symbols of the first 20 elements
  • Name compounds from given formulae
  • Write word equations
  • Write formulae and balanced chemical equations
  • Write balanced half equations and ionic equations (HT only)
• Many transition elements have ions with different charges, form

  coloured compounds and are useful as catalysts.
• Mixture

  Consists of two or more elements or compounds not chemically combined together
• Processes to separate mixtures

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• These physical processes do not involve chemical reactions and no new substances are made
• Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
• Plum pudding model

  Suggested that the atom is a ball of positive charge with negative electrons embedded in it
• The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• Nuclear model

  Replaced the plum pudding model
• Niels Bohr

  Adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances
• Theoretical calculations of Bohr agreed with experimental observations
• Proton

  Name given to particles with positive charge in the nucleus
• The experimental work of James Chadwick provided evidence to show the existence of neutrons within the nucleus
• This was about 20 years after the nucleus became an accepted scientific idea
• Relative electrical charges of particles in atoms

  Electrons equal to protons, atoms have no overall electrical charge
• Atomic number

  The number of protons in an atom of an element
• All atoms of a particular element have the same number of protons
• Atoms of different elements have different numbers of protons
• Atoms are very small, having a radius of about 0.1 nm (1 x 10-10 m)
• The radius of a nucleus is less than 1/10 000 of that of the atom (about 1 x 10-14 m)
• Almost all of the mass of an atom is in the nucleus
• Mass number

  The sum of the protons and neutrons in an atom
• Isotopes

  Atoms of the same element that can have different numbers of neutrons
• The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element
• Electronic structure

  The arrangement of electrons in an atom
• Electronic structure representation

  Can be represented by numbers or by a diagram
• The electronic structure of sodium is 2,8,1
• The elements in the periodic table are arranged in order of atomic (proton) number
• Groups

  Columns in the periodic table where elements with similar properties are found
• Elements in the same group have the same number of electrons in their outer shell