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85669
Chemical Periodicity
Descrição
GCSE Chemistry Mapa Mental sobre Chemical Periodicity, criado por James Lamming em 12-05-2013.
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chemistry
chemistry
gcse
Mapa Mental por
James Lamming
, atualizado more than 1 year ago
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James Lamming
mais de 11 anos atrás
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Resumo de Recurso
Chemical Periodicity
Periodicity is the repeating pattern of properties in elements.
This regularity allows elements to be placed in groups
Each element has similar, though gradually varying, properties
These properties are both chemical and physical
Electron structure
Electrons orbit the nucleus at certain fixed distances- SHELLS
Each shell can hold up a certain number of electrons
Shell 1- 2 Electrons
Shell 4- 2 Electrons
Shell 3- 8 Electrons
Shell 2- 8 Electrons
Electrons fill up the nearest shells first
Number of electrons in the outer shell= group number
All chemical reactions are the result of changes in the outer shell of electrons
All elements in a group have the same number of electrons in the outer shell
Therefore elements in any group have similar characteristics
However, as groups descends, more shells are added
More shells means more distance from the positively charged nucleus
Therefore it is harder to gain electrons but easier to lose them
GROUP 0- NOBLE GASES
Highly unreactive
Do not form compounds
Full outer shell of electrons
Colourless gases
Down the group they become
Denser
Gain a higher boiling point
USES
Helium
Airships
Party balloons
Neon
Filling gas discharge tubes for neon signs
Cryogenic refrigeration
Argon
Inside lightbulbs to stop filament oxidation
Food packaging to stop rotting
Krypton
Lasers
Killing Superman
Xenon
Flash camera bulbs
Strobe lights
GROUP 1 ALKALI METALS
Relatively low density
Potassium, Sodium and Lithium float on water
Shiny when first cut
Tarnish rapidly upon oxidation
Soft- can be cut by a knife
Low melting points
Silvery metals
Caesium is pale-gold colour
Very reactive- most reactive metal group
Stored under oil or under Argon atmosphere
They react with water to give Oxides
They react with water to give Hydroxides AND Hydrogen
These reactions are very vigorous
Lithium fizzes around on the surface of the water and seems to dissolve
Sodium fizzes around in a molten ball, appearing to dissolve
This is because Sodium has a lower boiling point than Lithium AND the reaction is more exothermic
Potassium fizzes around in a molten ball, igniting the Hydrogen from the reaction and producing a purple flame
The presence of Hydroxide products can be shown using an indicator
Hydroxides are alkaline, thus why the metals are also known as the 'alkali metals'
As the group descends...
The metals become more reactive
Become softer
Increase in density
The metals want to lose an electron to have a full outer shell
The further they are from the protons, the easier they can lose the electron
The more shells they have, the further they are from the protons.
As they descend the group, the become MORE reactive
GROUP 7- THE HALOGENS
Halogens are reactive non-metals
They are diatomic molecules
They have poisonous vapours
Halogens and their properties
Fluorine
Pale yellow
Highly toxic
Very reactive
GAS
Chlorine, Cl2
Pale green gas
Dense
Toxic
GAS
Bromine, Br2
Dense
Dark red
LIQUID
Gives off red/brown vapour
Toxic and Corrosive
Iodine
Dark grey
SOLID
Sublimes to give a purple vapour
Forms a brown solution in water and a purple one in Hexane
Astatine is radioactive and very unstable
They are ALL poor conductors of heat and electricity
On descending the group...
They become less reactive
They are trying to ATTRACT electrons, unlike the Alkali metals
This means they want to be nearer the protons and the nucleus
Therefore they want fewer shells between them and the nucleus
Their colour becomes darker
Their melting and boiling points INCREASE
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