GCSE C3 Chapter 1

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  • Created by: emma998
  • Created on: 13-03-14 16:05

The early periodic table

  • During the 19th century many new elements were being discovered and chemists were attempting to put these elements into a table of common groups
  • The scientists did not know about the structures of atoms
  • They tried to classify elements based on their atomic weights
  • In 1863 Newlands presented his idea about his law of octaves
  • He claimed that the properties of elements repeated themselves every 8th element
  • He used this to group all 62 known elements at time into 7 groups based on atomic weights
  • However after the element calcium the properties of elements did not match
  • So scientists did not accept his ideas
  • In 1869 Mendeleev used Newlands ideas to produce a better table of elements
  • He did this by leaving gaps for the undiscovered elements
  • He then used his table to predict the properties of undiscovered elements
  • When these elements were discovered he was proved right
  • So scientists more readily accepted his ideas
  • The table Menedeleev produced forms the basis of the modern periodic table
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The modern periodic table

  • Scientists found out about protons and neutrons at the start of the 20th century
  • Soon after this they developed models for the arrangment of electrons in atoms
  • In the periodic table the elements are arranged in groups according to their atomic number
  • The elements are lined up in vertical collumns called groups
  • Elements in the same group have similar properties because they have the same number of electrons in thier higheast energy level
  • Within a group the reactivity depends on the electrons in the highest energy level
  • Going down a group there are more occupied energy levels
  • Therefore the forces of attraction between the nucleus and the electrons in the highest occupied energy level is weaker

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The alkali metals

  • The elements in group one are called the alkali metals
  • They react readily with water and oxygen so must be sotred carefully
  • They react with halogens to produce salts that are white or colourless
  • Sodium + chlorine = Sodium chloride
  •  2Na(s)  +  Cl(g)    =    2NaCl(s)
  • They dissolve in water to produce white or colourless solutions which are alkaline
  • They are soft solids at room temperature with low melting and boiling points
  • They have low densities so lithium, sodium and pottasium float on water
  • They react with water to produce hydrogen gas and a metal hydroxide which is an alkali
  • Sodium +  water   =    sodium hydroxide +    hydrogen
  •  2Na(s) + 2H2O(l)  =        2NaOH(aq)      +      H2(g)
  • The reactivity increases going down the group because:
    • Going down the group more energy levels are occupied
    • Meaning the highest energy levels are further away from the nucelus
    • Therefore the forces of attraction between the nucleus and the electrons in the highest energy levels are weaker 
    • Therefore it is easier for the alkali metal to lose its electron in its highest energy level
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Transition elements

  • The transition elements are found in the periodic table between groups 3 and 4
  • They are all metals so sometimes called the transition metals
  • They have higher boiling points (except for mercury)
  • High densities
  • Malleable and ductile
  • React slowly if at all with oxygen and water at room temperature
  • Strong
  • Useful building materials often as alloys
  • React with non-metallic elements to produce positive ions with varous charges
  • Produce colourful compounds
  • Transition metals and thier compounds are used as catalysts in many reactions
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The halogens

  • The halogens are non-metallic elements in group 7 of the periodic table
  • They can also form covalent bonds with other non-metallic elements to form molecules
  • They exist as small molecules
  • They have low melting and boiling points that increase going down the group
  • At room temperature:
    • Flourine is a pale yellow gas
    • chlorine is a green gas
    • Bromine is a brick-red liquid
    • Iodine is a grey solid which easily vapourises into a violet gas
  • Form charges with -1
  • Their reactivity decreases going down the group because:
    • Halogens need to gain electrons to become stable
    • More occupied energy levels
    • Highest occupied energy level is further away from the nucleus
    • So forces of attraction between nucleus + electrons in highest energy level decreases
    • Meaning it is harder for the atoms to gain electrons
  • A more reactive halogen can to displace a less reactive halogen from an aq solution
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