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CHEMISTRY…read more

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Number of neutrons = number of protons ­ atoms
have no overall electrical charge
Compounds chemically bonded, formed when 2 or
more elements chemically react,
Chemical bonds either by transferring or sharing
When transferred they form ions
Group 1 ­ alkali metals ­ react with non-metal
elements to form ionic compounds in which the
metal ion has a single positive charge
Group 7 ­ halogens. React with alkali metals to
form ionic compounds in which the halide ions
have a single negative charge…read more

Slide 3

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Very strong chemical bonds between all ions
Single crystal of salt=one giant ionic lattice
High melting/boiling point ­ due to strong
chemical bonds
Dissolve to form solutions that conduct
electricity. When dissolved ions separate ­
free to move in the solution and carry electric
current. Dissolved lithium salts used to make
rechargeable batteries.
Conduct electricity when molten, when it melts,
ions free to move and they carry electric
currents.…read more

Slide 4

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Weak intermolecular forces
Low melting/boiling points. Molecules easily parted from each other
Most molecular substances= gases/liquids at room temp.
Don't conduct electricity ­ no ions and no overall electric charge
Usually tell a molecular substance from its physical state ­ `'mushy'' e.g.
Liquid/gas/easily melted solid
Strong covalent bonds
Very high melting/boiling points
Don't conduct electricity- not even when molten
Usually insoluble in water.
DIAMOND: each carbon atom forms 4 covalent bonds in a rigid GCS, used for drill tips.
Hardest natural substance
GRAPHITE: each carbon atom forms 3 covalent bonds, creating layers, free to slide over
each other, layers held loosely can be rubbed onto paper. Leaves free electrons,
graphite only non mental that is a good conductor of electricity. Soft and slippery. One
electron from each carbon atom is delocalised. Allows graphite to conduct heat&
SILICA: can be melted with sodium carbonate and limestone to make glass…read more

Slide 5

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Metal properties due to `sea of free electrons'
Metals conduct heat and electricity because of the
delocalised electrons in their structures
Free electrons come from outer shell of every
metal atom in the structure
Electrons free to move therefore good conductors.
Electrons hold atoms together in a regular
structure and allows the atoms to slide over each
other=metals malleable and ductile
High melting/boiling points…read more

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Smart materials
Behave differently depending on their
conditions e.g. Nitinol
Dyes that change colour depending on
temperature or light intensity
Liquids that turn solid when put in a
magnetic field
Materials that expand/contract when an
electric current goes through them…read more

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