Unit 1: 3 Bonding
BONDING
>Atoms are held together in compounds by chemical bonds
>Bonds between atoms involve ELECTRON TRANSFER.
>atoms bond together in order to achieve a stable electronic structure like a noble gas.
>There are 3 types of chemical bonds - ionic, covalent and metallic.
Ionic bonding
-Compounds formed between metals and non-metals are ionic compounds.
-An ionic compound is made up of a lattice of positively charged metal ions and negatively
charged non-metal ions.
IONIC BONDING is the force of attraction between the positive and negative ions that form an
ionic compound. Electrostatic forces of attraction are formed when electrons are transferred from
the metal to a non-metal; the metal atom loses its higher energy electron(s) forming positive ions
(cations) whilst the non metal gains electron(s) into its higher energy level to form negative ions
(anions).
Properties of ionic compounds;
The model for an ionic solid consists of a giant ionic lattice
containing a regular arrangement of positive and negative ions.
I.
Ionic compounds have very high melting and boiling points there are strong electrostatic forces of attraction that exist
between the oppositely charged ions in the lattice that require
a lot of energy to overcome; therefore high mp and bps.
II.
Ionic compounds can conduct electricity when molten - when melted, the lattice breaks
down and the ions are free to move, mobile ions will be able to carry charge through the
liquid and therefore can conduct electricity.
III. Ionic compounds are brittle, they shatter when hit or given a sharp blow. A sharp blow can
cause the ions in the lattice to displace and similarly charged particles come into contact
with each other. The repulsion between like charges causes the structure to shatter.
ELECTROSTATIC FORCES OF ATTRACTION INCREASE AS;
- the charge on the ions increase
- the size of the ions decrease.
CHEMISTRY AS NOTES
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Unit 1: 3 Bonding
Covalent Bonding
A covalent bond is formed when a pair of electrons is shared between 2 atoms (usually nonmetals)
COVALENT BONDING involves the sharing of a pair of electrons between two atoms. A
covalent bond is formed when two atomic orbitals. each containing a single unpaired electron,
overlap. Each atom is then attracted to the nuclei of both atoms. It is this attraction that holds the
atoms together in a covalent bond.
COVALENT BONDS are stronger if the degree of overlap between the orbitals is greater.
Dot & Cross Diagrams
In the displayed formula, a line
between the atoms is used to
represent the covalent bond.
If atoms share more than one
pair of electrons, more than
one line is used.
Coordinate or Dative Covalent Bonding
This is where a covalent bond is made between two atoms whereby one of the atoms donates
both the electrons - a LONE PAIR - to form the bond.
We represent a dative bond as an arrow.
CHEMISTRY AS NOTES
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