The periodic table

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  • Created by: Shereen
  • Created on: 17-03-13 16:50

Early periodic table

During 19 th century many elements had been discovered, scientist tried to classify elements based on properties and atomic weights

1863- Newlands proposes law of Octaves. It stated that similar properties are repeated every eighth element. He put the 62 known elements into seven groups according to atomic weight. After calcium, properties did not match and no spaces were left for unknown elects. Scientists did not accept his ideas

1869- Mendeleev produces a better table. He left spaces for unknown elements so that the groups had similar properties. He predicted the properties of the undiscovered elements, once they were discovered scientists accepted his ideas. He also ordered elements according to atomic mass, not weight. He provided the basis for the modern periodic table

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Modern periodic table

Scientist found out about protons and electrons at the start of the 20th century. They developed models of the atoms electronic arrangements. Ordered the periodic table in order of atomic number and were lined up in vertical groups

The groups of atoms have the same properties because they have the same amount of electrons in their outer shell.

Reactivity in elements depends on total number of electrons. Going down a group there are more occupied energy levels. As atoms get larger the outer shell electrons are less strongly attracted by the nucleus, therefore more reactive

Metals-react they lose electrons, so the reactivity of metals increase going down a group
Non metals- react they gain electrons, so reactivity of non-metals decreases going down a group

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Group 1 alkali metals

All alkali metals react readily with air and water, which is why they are stored in oil.
They are soft solids at room temperature, low ,eating and boiling points that decrease going down the group. Low densities so Li, Na and K float on water

React wth water to produce metal hydroxide and hydrogen gas.
Eg, 2Na+2H2O-->2NaOH+H2

They lose their electrons in reactions to form ionic compounds, ions have a single positive charge
React with halogens to form salts that are a white or colourless crystal
Compounds of alkali metals dissolve in water, forming colourless solutions
Reactivity increases going down group 1 because larger atoms, electron are less attracted to nucleus,
Loss of an electron-oxidisation
Gain an electron-reduction

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Transition metals

Transition elements are all metals, with the exception of mercury they have higher melting and boiling points than the alkali metals
They are malleable and ductile, and are good conductors of heat and electricity
They react slowly or not at all with oxygen and water at ordinary temperatures
Most are strong and dense, often used as building materials
They form positive ions with various charges
Many transition metals and their compounds can be used as catalysts for reactions, for example, manganese oxide is used to decompose hydrogen peroxide.

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Halogens- Group 7

Halogens are all non metallic elements
They're exist of small molecules made up of two atoms (diatomic) low melting and boiling points, increase as you go down the group
Fluorine is a yellow gas, chlorine is a green gas, bromine is a red liquid and iodine is a grey solid, iodine easily vaporises to a violet gas

Halogens form Halide ions with a 1- charge, they bond covalently to form molecules
Reactivity on increases going down. A more reactive halogen displaces a less reactive halogen in a chemical reaction, to form an aqueous solution of a halide compound.

They react with metals to form a salt or metal halide

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