Periodic table revision

Periodic table revision

1. The periodic table

   • Groups- The vertical columns, called groups, contain elements with similar properties. The group indicates the number of electrons in the outer shell
   • Periods- The horizontal rows, called periods, contain elements displaying a gradual change in properties. The period number indicates the number of electron shells
   • Metal/non-metal- The bold line on diagrams of the periodic table divides metals on the left, and non-metals on the right

2. development of the periodic table

   • before the discovery of atomic structure, scientists attempted to classify the elements by arranging them in order of their atomic weights. However, many early tables were incomplete, and some elements were placed in unsuitable groups
     • Today's periodic table is based on one devised by a Russian scientist named Dmitri Mendeleev in 1869. Mendeleev ordered the elements according to atomic weights . However, he realised that there may be undiscovered elements and so left gaps in his table. He also ordered the elements in consideration of their chemical properties

3. Metals & non-metals

   • When atoms react, they either lose or gain electrons to form a full outer shell. Atoms that lose electrons form positive ions, and atoms that gain them form negative ions
     • Metals have fewer electrons in their outer shell so are more likely to lose electrons and form positive ions
     • Non- metals have more electrons in their outer shell so are more likely to gain electrons and form negative ions
       • Non-metals that form negative ions can react with metals to form ionic compounds. Metals cannot react with other metals because positive ions repel each other. Non- metals that do not form ions can share electrons with each other to form molecules with covalent bonds

4. Alkali metals

   • Group 1 is known as the Alkali metals. They only have one electron in their outer shell. Therefore, they are very reactive.
     • As you move down the group, the elements become more reactive. This is because the outer electron is further from the nucleus- meaning there is a weaker force of attraction between them. Therefore, melting and boiling points decrease as you go down the group
       • physical properties include: -Low density -soft & malleable -Conducts electricity

5. Noble gasses

   • Group 0 is known as the noble gases. They have a full outer shell of electrons. Therefore, they don't need to gain or lose electrons to become stable- making them inert
     • Group 0 are monatomic,and their boiling points increase down the group. this is because the intermolecular forces between the atoms increase as the size increases
       • physical properties: -colourless -low melting point -inert -non-flammable -non-metal

6. Halogens

   • Group 7 is known as the Halogens. They have seven electrons in their outer shell. They are diatomic, joined by a single covalent bond.
     • As you move down the group, the elements' reactivity decreases whereas the molecular mass and melting/boiling points increase. This is due to the outer shell being further away from the nucleus, making it harder to attract electrons
       • physical properties: -toxic -coloured -low melting/boiling points -poor conductors

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