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The halogens- Fluorine, bromine, Iodine

The halogens are diatomic molecules. They are toxic and corrosive

A diatomic molecule= a molecule with two atoms eg. chlorine (Cl2)

Order of reactivity= Flourine, Chlorine, Bromine, Iodine

Clourine (Cl2)= A gas with a boiling point of -35. Is pale green/yellow at room temperature. It bleaches an indicator. Is highly reactive with Iron wool

Bromine (Br2) = A liquid witha boiling point of 54. It red/brown at room temperature and has a red/brown colour when a gas. Is slightly reactive with iron wool

Iodine= A sold with a boiling point of 184. Is grey at room temperature and has a purple colour when a gas. It has a small level of reactivity with iron wool.

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Displacement of the halogens

Displacement reaction= A reaction in which a halogen in a salt is displaced with a more reactive halogen to form a new ionic salt (compound)

eg. Cl2 + 2NaI ---> I2 + 2NaCl

The reactivity of the halogens increases as you go down the group. The most reactive is flourine.

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Atomic structure

Electron shell rules:

first shell = 2 electrons

secound shell = 8 electrons

third shell = 8 electrons

fourth shell = 8 electrons

electons in different shells have different energy levels- the closer the electon shell is to the nucleus th lower the energy level

Group 7 = 7 electrons in outer shell

Group 4 = 4 electrons in outer shell       (this is why proporties in the same group react simularly)

number of protons + number of neutrons = relative atomic mass

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Ionic bonding

An ion is an atom with a charge.

All elements want a full outer shell of electrons.

Ionic bonding occurs between a metal and a non metal.

The metal gives up an electron(s) so that it has a full outer shell of electrons. It becomes positive. This electron(s) is taken by the non metal so that it also has a full outer shell. The gain of electrons makes it negative. As the elements are now of opposite charge they are attracted together and are bonded.

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Properties of salts

  • Salts do not conduct electricity because the ions are unable to move. However if salts are melted or dissolved then the ions are free to move and can conduct electricity
  • High melting and boiling points
  • Giant ionic regular lattices
  • Held together by electrostatic forces
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Spectroscopy

All atoms give off light when heated. When this light is split up, each element has its own unique line spectra. Scientists have used spectroscopy to discover new elements.

Helium was discovered by spectroscopy when scientists looked at the line spectra from the sun

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The discovery of the periodic table

The modern periodic table is based on Russian chemist Dmitri Mendeleev's ideas. He arranged the elements into groups and periods on their relative atomic masses and patterns in their properties. He left gaps for undiscovered elements and predicted properties of missing elements

John Newlands noticed an 'octaves' pattern, where every eigth element had similar properties.

Johann Dobereiner noticed 'triads' that linked patterns of the relative atomic masses for three elements

The periodic table is now ordered by proton number

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The alkali metals (group 1)

Group one is called the alkali metals. They all have a single electron in their outer shells.

Some properties of alkali metals are that they are soft and can be cut with a knife. The freshly cut surface is shiny but tarnishes quickly by reacting with oxygen.

Reactivity increases as you move down the group.

THEY ARE HIGHLY REACTIVE

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Group one reactions with water and chlorine

All group one metals react with water. The general equation for this is:

metal + water ---> metal hydroxide + hydrogen

Hydrogen can be identified by the pop test and can be explosive

If M represented any group 1 metals the general equation is:

2M(s) + 2H20(l) ---> H2(g) + 2MOH(aq)

Sodium reacts vigorously with chlorine to give a yellow flame, it makes a colourless cystaline salt ( sodium chloride). The word and symbol equation for this is:

Sodium + Chlorine ---> Sodium chloride

2Na(s) + Cl2(g) ---> 2NaCl(s)

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