Topic 1 - Atomic Structure and the Periodic table

• what is an atom?

  The smallest part of an element that can exist on its own
• What is an element?

  A substance that contains only one sort of atom
• Mixture


  Two or more elements or compounds that are not chemically combined and does have the same properties as its original element
• Compound


  Contains atoms of two or more elements, which are chemically combined in fixed proportions and have different properties to their original element
• Mixtures


  • Components retain their own properties
  • Can be separated by physical processes (no new substances made)
• The total mass of the products of a chemical reaction is always equal to the total mass of the reactants
• The products of a chemical reaction are made from exactly the same atoms as the reactants
• Elements are displayed in the periodic table
• Chemical symbol


  Represents an atom of a particular element
• Chemical formula


  Combination of numbers and chemical symbols to show the different elements in a compound and how many atoms of each element one molecule contains
• Compounds can only be separated into their component elements by chemical reactions like electrolysis
• Atoms contain three types of subatomic particle: protons, neutrons and electrons
• Atomic number


  The number of protons in an atom
• Mass number


  The sum of the protons and neutrons in an atom
• Atoms of different elements have different numbers of protons
• Isotopes of an element have the same number of protons but a different number of neutrons
• Ion


  An atom that has gained or lost electrons, becoming charged
• Electron configuration


  Shows how the electrons are arranged around the nucleus in shells
• The first shell can only hold a maximum of two electrons, the next two shells can each hold a maximum of eight electrons
• Ion

  9 protons, 10 electrons, 10 neutrons
• Electrons in an atom

  • Occupy the lowest available shell or energy level
• Fluorine


  A non-metal
• Mendeleev tried to put together a periodic table in 1864 when many elements were still undiscovered
• Mendeleev arranged the known elements in order of atomic weight, which revealed repeated patterns but also problems with missing elements
• Mendeleev realised some elements were in the wrong place when following the order of atomic weight, so he left gaps for undiscovered elements and reordered some elements when creating his table in 1869
• Mendeleev placed each element in a vertical column or 'group' with elements that had similar properties
• When subatomic particles were later discovered, it revealed Mendeleev had organised the elements in order of increasing atomic number (number of protons)
• Group 0 (noble gases)

  • Have a full outer shell of electrons, very stable electron configuration, very unreactive non-metals
  • Boiling points increase down the group
• Group 1 (alkali metals)


  • Have one electron in their outermost shell
  • Have low melting and boiling points that decrease down the group
  • Become more reactive down the group as the outer electron gets further from the nucleus and can be lost more easily
  • Stored under oil as they react vigorously with oxygen and water
• When alkali metals react with water


  1. A metal hydroxide is formed

  2. Hydrogen gas is given off
• Potassium reacts with water

  Potassium hydroxide + hydrogen
• Group 7 (halogens)


  • Have seven electrons in their outermost shell
  • Consist of molecules made of pairs of atoms
  • Reactivity decreases down the group as the outer shell electrons get further from the nucleus
  • Relative molecular mass, melting point and boiling point increase down the group
• Halogens react with metals

  1. To produce ionic salts

  2. The halogen atom gains one electron to form a halide ion with a negative charge
• A more reactive halogen


  Will displace a less reactive halogen from an aqueous solution of its salt
• Transition metals


  • Are in the centre of the periodic table, between Groups 2 and 3
  • Form coloured compounds
  • Have ions with different charges
  • Can be used as catalysts
  • Are good conductors of heat and electricity, can be easily bent or hammered into shape
• Mendeleev designed the periodic table
• Group 0 elements are unreactive
• Alkali metals are stored in oil
• Properties of transition metals

  • Stronger
  • Harder
  • Denser
  • Have higher melting points
  • Less reactive than alkali metals