The periodic table and its development

The early periodic table
1. Newlands' law of octaves
  1. Spotted a pattern when arranging elements in order of atomic mass
  2. Noticed properties of elements repeat every eighth element
    1. 'Law of Octaves'
  3. Inconsistencies in his method meant his ideas weren't accepted at the time
2. Mendeleev's achievement
  1. Same idea as Newland but noticed undiscovered elements which he left gaps shown by * in the table
    1. Allowed him to organise table in a repeating pattern
  2. Elements with similar properties occur in groups at regular intervals - periods
3. Changing the order
  1. Following the discovery of protons, neutrons and electrons, it became clear that elements should be placed in order of atomic number not mass
  2. Mendeleev thought the atomic masses of some elements had been measured inaccurately but he'd placed the elements in order of atomic number without realising
  3. Mendeleev's table was accepted because of his remarkable predictions turning out to be correct
The modern periodic table
1. Structure
  1. Elements are arranged by proton number
    1. Making elements naturally fall into groups with similar properties
2. Electronic Structure and the periodic table
  1. Atomic number describes the number of protons in the atom
    1. Therefore also the number of electrons and their arrangement around the nucleus
  2. Pattern is directly linked to the way in which electrons are arranged around the atoms of each element
  3. Period number tells you how many energy levels containing electrons the element has
  4. Group number tells you how many electrons an element has in its outer energy level
  5. Periodic table predicts the chemical properties of elements
3. Metals
  1. Found in the middle and on the left of the periodic table
  2. Groups 1 and 2 contain very reactive but quote soft metals with low melting points
  3. The transition metals block contains 'everyday' metals such as iron and copper
    1. Not as reactive as group 1 and 2 but are harder, stronger and have higher melting points
4. Non-metals
  1. Found to the right of the table
  2. Groups 6 and 7 contain reactive non-metals
    1. Gases at the top but solids further down
  3. Group 0 contains the Noble gases, highly un-reactive metals
5. Groups 3,4 and 5
  1. Elements at the top are non-metals
    1. More metallic as you move down
  2. Boundary between non-metals and metals zig-zags down the right
  3. Elements on the boundary show intermediate properties between non-metals and metals
    1. semi-conductors e.g. silicon
Group 1 - the alkali metals
1. Physical properties
  1. All soft and conduct heat and electricity
  2. Freshly cut is shiny but soon tarnishes in the air
  3. etals have low density and relatively low melting and boiling points
2. Typical chemical reactions
  1. React with water and oxygen in the air (which is why they tarnish)
    1. Put in oil to stop this from happening
  2. All have one outer electron
    1. When they react, they lose this electron and form 1+ions
  3. When they react with non-metals, they form ionic compounds
    1. These compounds are white and dissolve in water to form colourless solutions
  4. When reacted with water, they form a metal hydroxide and hydrogen
    1. The metal hydroxides dissolve in water, making an alkaline solution.
3. Trends in chemical properties
  1. Reactions get more vigorous as you go down
    1. Because alkali metals react by losing their lone outer electron
  2. Atoms get bigger as you go down the group as more energy levels are added
    1. Means lone outer electron is further away from positive nucleus increasingly screened by the inner electron shells
      1. Reduces attraction from the nucleus to the outer electron and makes the electron easier to lose
      2. The bigger the atom, the more reactive the metal
Transition metals
1. 'Everyday' metals
  1. Include most of the metals used for Construction, Machinery, Vehicles, Wiring etc.
  2. Conduct heat and electricity
  3. Compared with group 1 metals, the transition metals:
    1. Higher melting points
    2. Higher densities
    3. Stronger and harder
    4. Much less reactive
2. Special properties
  1. Catlysts
  2. Compounds containing transition metals are usually coloured
    1. Some statues and roofs are made of copper
    2. Many gemstones are coloured by transition metal compounds
    3. Used in some paint pigments and ceramic glazes
Group 7 - Halogens
1. Coloured non-metals
  1. Non-metals with coloured vapours
  2. All made of molecules
  3. They don't conduct heat or electricity
  4. Low melting and boiling points
    1. Forces between molecules are weak
2. Chemical Properties
  1. All react with metals to form ionic compounds containing halide ions
  2. Electrons are transferred from the metal atoms to the halogen atoms, forming halide ions with a 1- electric charge
  3. Halogens react with non-metals to form molecular compounds containing covalent bonds
    1. Electrons are shared between atoms
3. Reactivity
  1. ess reactive as you go down the gorup
  2. When reacted the atoms gain an electron
    1. Atoms get bigger down the gorup
      1. Electron gained is further from the nucleus
        Attraction of the nucleus for the electron being gained is weaker and so the electron is harder to gain
  3. A more reactive halogen will displace a less reactive halogen from a compound in a displacement reaction

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