So 10M have a chemistry test next Friday on
structures and bondings; you might find this a bit long but it has everything
you need to know about structures and all that other stuff and I’ve kept it to
a bare minimum so you don’t have to learn loads.
Chemistry
The
different types of structure considered here are:
- Metallic (two metals)
- covalent bonds (two non-metals)
- ionic (non-metal and metal)
Metallic structure
A metallic structure consists of
a giant lattice of
positively charged ions and delocalised outer electrons.
Metals are malleable - they can be bent and shaped. This is because
they consist of layers of atoms.
These layers can slide over one another when the metal is bent, hammered or
pressed.
Metals
- Higher tier
Metals form giant structures in which
electrons in the outer shells of
the metal atoms are free to move. The metallic bond is the force of attraction
between these free electrons and metal ions.
Metallic bonds are strong, so metals can maintain a regular structure and
usually have high melting and boiling points.
Metals are good conductors of electricity and heat. This
is because the free electrons can move throughout the metal.--------------------------------------------------------------------------------------------------------------------------
A COVELANT BOND - is a
strong bond between two non-metal atoms.
It consists of a shared pair of electrons.
A covalent bond can be represented by a straight line or dot-and-cross diagram.
Covalent molecular structure (between two non-metals)
|
Covalent network structure
 |
A
covalent network structure consists of a giant lattice of covalently bonded
atoms.
|
Covalent bonds form between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong. Covalently
bonded substances fall into two main types:
1.
Simple molecules
2.
Giant covalent structures
PROPERTIES
Properties of simple
molecular substances
·
Low
melting and boiling points - This is
because the weak intermolecular forces break down easily.
·
Non-conductive - Substances with a simple molecular
structure do not conduct
electricity. This is because they do not have any free electrons or an overall
electric charge.
Properties of giant
covalent structures
·
Very high
melting points -
Substances with giant covalent structures have very high melting points,
because a lot of strong covalent bonds must be broken. Graphite, for example,
has a melting point of more than 3,600ºC.
·
Variable
conductivity - Diamond
does not conduct electricity.
Graphite contains free electrons,
so it does conduct electricity. Silicon is semi-conductive - that is, midway
between non-conductive and conductive.
-------------------------------------------------------------------------------------------------------------------------
IONIC
BOND
- An ionic bond is
formed between metals and non-metals. The metal donates one or more electrons
to the non-metal. This causes the metal to become positively charged (as it has
lost at least one electron) and the non-metal to become negatively charges (as
it has gained at least one electron). This attraction between the positive
metal ions and the negative non-metal ions causes a bond (ionic bond) to be
formed.
Ionic structure
An ionic structure consists of a giant lattice of
oppositely charged ions.
An ionic
bond is between a metal and a non-metal.
PROPERTIES
Melting points and
boiling points
Ionic bonds are very strong so a lot of energy is
needed to break them. Ionic compounds contain many of these strong bonds so
they have high melting and boiling points.
Conduction of electricity
Ionic
compounds conduct electricity
when they are dissolved in water or when they are melted. This is because their
ions are free to move and carry the current. However, ionic compounds do not
conduct electricity when they are solid. This is because their ions cannot move
around in their lattice
structure.
This test is for 10M... hope we all do well. she said it would be pretty easy (i hope)
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