Bonding

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Bonding
Types of Bonding
Ionic Bonding
An attraction between oppositely charged ions which are formed by the transfer of electrons
from one atom to another
Can form giant ionic structures
Properties
· High boiling and melting points (Needed to break strong electrostatic forces
· Can conduct electricity when molten or in solution (free ions)
· Usually hard and brittle
· Soluble in water
· Solid at room temperature
· Low thermal conductivity
For example, in sodium chloride, each sodium atom has to transfer an electron to a chlorine atom.
The result is a sodium ion and a chloride anion, these two attract each other and form a stable
compound.
oo
Na o o
Cl o
x
oo
+ -
oo
o o
Na Cl
x o
oo
+ -
oo
o o
Na Cl
x o
oo
Covalent Bonding
A pair of electrons shared between two atoms
Normally atoms of non-metals
Properties
· Usually liquid or gas at room temperature
· Low melting and boiling points
· Usually insoluble in water
· Poor conductors
· Soft in comparison to ionic
· Can form simple molecules or giant structures
In a standard covalent bond, each atom provides one electron to the bond, it is represented as a
single short straight line between the two atoms.

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Covalent bonding happens as the electrons are more stable when attracted to two nuclei rather than
one . Covalent bonds should not be regarded as shared electron pairs in a fixed position, they are in
a state of constant motion and are best known as charge clouds.…read more

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Mg e Mg
e
e
Electronegativity
The ability of an atoms to attract electrons in a covalent bond
The electronegativity of an atom depends on its ability to attract and hold onto electrons.
Electronegativity increases across the periods as the nucleur charge increases but the shielding stays
the same and so the electrons are strongly attracted to the atom. In turn, electronegativity would
decrease down a group as the shielding increases as the electrons are less attracted to the atom.…read more

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Metallic
If both atoms are electropositive neither can attract the electrons and so the electrons are free to
move about, both atoms gain a positive charge and the bond is metallic.
2+ 2+
x
o
Mg Mg
x
o
So if sufficient electronegativity data is given, it is possible to decide whether a bond between two
atoms is metallic, ionic, polar covalent or covalent:
· Less/between 1.6-1.9 the bond is metallic
· Either atom has a value greater than 1.…read more

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Valence shell electron pair repulsion theory
· Valence shell electron pairs are arranged to minimise repulsions between themselves
· Order of repulsion strength: lone pair-lone pair> lone pair- shared pair> shared pair-shared
pair
· When there are five or more electron pairs, neglect repulsion between electron pairs at an
angle greater than 90 degrees
· Basic geometry is still determined by number of electron pairs
· Lone pair repulsion>Double bond repulsion> Bonding pair repulsion>
How to work out molecule shape…read more

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Distorted Shapes
Because of the presence of lone pairs, molecular shapes can sometimes be distorted, this is because
lone pairs repel more than bonding pairs/shared pairs.
Ammonia
· Three bonding pairs and a lone pair
· Based on tetrahedral, due to extra repulsion from lone pair, the 3 N-H bonds bend further
away from lone pairs to minimise repulsion.…read more

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Hydrogen Bonding in Water
During the formation of a hydrogen bond, the electron in each hydrogen atom is pulled tightly to
the nearly full oxygen valence shell in a covalent bond. This tight draw toward the oxygen creates a
partial negative charge on the other side of the oxygen and a partial positive charge on the hydrogen
atom. These partial bonds are then attracted to one another, creating a secondary bond between
molecules.…read more

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