chem modelsofbondingandstructure
Structure 2.2.1 - a covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei
the octet rule refers to the tendency of atoms to gain a valence shell with a total of eight electrons.
covalent bond forms by atoms sharing electrons, to gain valence electrons in order to achieve the stable electron structure of a noble gas. the shared pair of electrons is concentrated in the region between the two and is attracted to both. the electrostatic attraction between the shared pair of electrons and the positively charged nuclei holds the atoms together and is known as a covalent bond.
- the bond is stabilised when the force of attraction between the nuclei and shared electrons are balanced by the force of repulsion of the two nuclei
octet rule
elements want to gain a valence shell with a total of eight electrons
the ability of two identical atoms to form a covalent bond is due to the similar strength with which they attract valence electrons.
Lewis formulae
represent all valence electrons as dots or crosses. represent bonds as a line :)
when drawing structure of ions, put in square brackets with charge outside
exceptions and limitations
small atoms form stable molecules in which the central atom has less than eight electrons in its valence shell.
hydrogen, beryllium, boron, aluminium can form incomplete octets. this is due to the small size of the atoms which limits the number of atoms that can get close enough to share the required number of electrons for a complete octet.
central atoms can also have more than 8 valence electrons, known as an expanded octet. read 2.2.14 formal charge (HL)