5.3 covalent bonding Flashcards
define
covalent bond
The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded
atoms.
where does covalent bonding taker place
Covalent bonding takes place in diatomic elements, in compounds of non-metallic elements,
and between the atoms of polyatomic ions
explin what is meant by a localsied bond
a covlent bond is an example of a……
Localised bond
Unlike ions in an ionic bond, which attract in all directions, a covalent bond has an attraction
that is localised. The attraction acts solely between the shared pair of electrons.
how many bonds do these elements form
C,O,N,H
Carbon forms 4 bonds
Nitrogen forms 3 bonds
Oxygen forms 2 bonds
Hydrogen forms 1 bond
This allows each of these elements to have a filled outer shell, and thus obey the octet rule –
giving them a greater stability and allows them to resemble the desired noble gas configuration.
However, there are exceptions to the rule: Boron, Phosphorous, Sulfur and Chlorine.
4 exceptions to the octect rule
- Boron- boron only has 3 available bonding electrons forms thigs like BF3 predictions to boding cannot be based soley on noble gas electron structure,
- Phosphorous, Sulfur and Chlorine. for elements in period 2 outer shell can hold max 8 e- but n3 can hold up to 18 so Cl S and P have more electrons available for bonding eg ClF ClF3 ClF3 ClF5 ClF7
known as the expansion of the octet only possible for n=3
Boron exception:
Boron has 3 electrons in the outer shell, and each pair up to form 3 bonding pairs. In total this gives Boron 6 electrons inthe outer shell.
This is a deviance from the otherwise desired 8 – but Boronis stable in this arrangement.
BF3 (boron trifluoride) is trigonal planar.
exception Phosphorous, Sulfur and Chlorine.
Phosphorous, Sulfur and Chlorine.
Phosphorous, sulfur and chlorine when bonding with (mainly) fluorine can gain that idea of 8
electrons in its outer shell (full 3p orbital)
