Atoms

are the smallest particles of an element.

Atomic Orbital

is the space around the nucleus where the probability of finding the electron is maximum. "House of the electron”.
An allowed energy state for an electron in an atom: the orbital is described mathematically by a wave function.
The three dimensional distribution of electron density is described by the square of the wave function.

Bond

is a force of attraction between atoms that result through sharing or transfer of electrons.

Bond angle

The covalent bond is directional in nature (unlike the electrovalent bond)thus in methane the sp3 hybrid orbitals of carbon atom will overlap with the s orbitals of hydrogen forming four bonds which tend to move away from each other as far as possible this leads to a tetrahedral arrangement with an angle of 109^o 28'. The bond angle depends on the state of hybridisation, the number of lone pairs and the strain in the system (in ring systems).

Chemical bond

is a force that binds two atoms together.

Chemistry

Chemistry is the study of conversion of matter from one form to another and the energetics involved.

Co-ordinate bond

is a bond formed when the same atom donates both electrons necessary for bond formation. It is also called a dative bond.

Covalent bond

is a force that binds two atoms through sharing a pair of electrons.

Electronegatvity

the capacity of an atom or group of atoms to attract electrons towards itself. In the periodic table electronegativity increases from left to right in a period and decreases down a group. Flourine is the most electronegative atom followed by oxygen and then Nitrogen.

Electrovalent bond

is an electrostatic force of attraction between two ions of opposite charge. It is also called ionic bond.

Hybridisation

A process of interaction(mixing up) of two or more atomic orbitals producing new bybrid orbitals. (Mixing is not the right term but is still used to convey an idea)

Hybridisation sp3

one s orbital and three p orbitals mix up producing four new hybrid orbitals called sp3 hybrid orbitals.
In methane the carbon atom is sp3 hybridised, one s orbital and three p orbitals of carbon mix up producing four new hybrid orbitals. Such a carbon does not have any unhybridised orbitals, the bonding involves only hybrid orbitals.

Hybridisation sp2

one s orbital and two p orbitals mix up producing three new hybrid orbitals called sp2 hybrid orbitals.
In ethene the two carbon atoms are both sp2 hybridised. one s and two p orbitals of each carbon mix producing three hybrid orbitals. Such an atom has three hybrid and one unhybridised p orbitals which will take part in bonding.

Hybridisation sp

one s and one p orbitals mix up producing two new hybrid orbitals called sp hybrid orbitals. In ethyne the two carbon atoms are both sp hybridised. one s and one p orbital of each carbon mix up producing the two new hybrid orbitals. Such an atom has two hybrid and two unhybridised p orbitals which will take part in bonding.

Hybrid orbital

An atomic orbital which results due to a combination of usually two other atomic orbitals, example sp3, sp2 orbitals, which result out of combination of s and p orbitals. Atomic orbital for which the wave function has been generated by mathematical combination of other wave functions (usually for s and p orbitals) in a single atom.

Hydrogen bond

The electrostatic attraction between an electronegative atom and a hydrogen atom which is linked to an electronegative atom. (usualy oxygen or nitrogen)

Ions

are atoms or a group of atoms with a charge.

Lewis structure

shows the atoms that are bonded together and the locations within the molecule of all bonding and nonbonding valence electrons. A covalent bond is shown as a pair of electrons placed exactly between the atoms or by a line joining the two atoms.

Lone pair

is a pair of electrons in the outer most level which has not taken part in bonding.

Molecular orbital

is an orbital derived from the interaction of two or more atomic orbitals. The molecular orbital can be bonding or antibonding. Electrons occupying the bonding molecular orbital (BMO) contribute towards bonding and occupation of electrons in the antibonding molecular orbital (ABMO)
does not lead to bonding.

Molecule

is the smallest particle of a compound, which is the result of a combination of two or more atoms through bond formation.

Nodal plane

A region (usually a plane) of an atomic or molecular orbital that separates lobes of opposite phase. At the nodal plane the electron density for that orbital is zero.

Non polar molecule

Usually molecules without electronegative atoms will be non polar in nature.

Octet rule

(Proposed by G.N.Lewis) stes that atoms share transfer or accept electrons in order to achieve an octet (or the nearest noble gas configuration) in its outermost shell which represents stability.

Orbital overlap

The interaction either favourable or unfavourable between orbitals of two or more atoms that results from their occupying the same region in space.

Phase

In phase: A term describing the interaction between atomic orbitals of two different atoms that leads to a bonding molecular orbital. This results from overlap of lobes for which the wave function has the same (opposite) sign or phase.

Pi bond

A bond that results through overlap of two atomic orbitals such that the overlap zone is not in the same inter nuclear axis. This is possible through lateral (sideways) overlap of two p-orbitals.

Polar bond

When two atoms of different electronegativity are linked by a covalent bond, the electron density is unequally shared. There is greater polarisation (shift) of electron density towards the atom of higher electronegativity, which therefore acquires a partial negative charge and the other atom acquires a partial positive charge. The bond thus has polarity and has a polar character.

Polar molecule

A molecule with polar bonds is a polar molecule . There are however some molecules which are nonpolar inspite of having polar bonds, CCl₄ is an example.

Sigma bond

A bond that results through overlap of two atomic orbitals such that the overlap zone is in the same internuclear axis.

Single bond

is a result of sharing two electrons between two atoms, each atom contributing one electron (equal sharing). This is normally represented in a structural formula by a line joining the two atoms. Similarly a double bond and a triple bond is the result of sharing two pairs and three pairs of electrons between two atoms respectively, these are represented by two or three lines joining the two atoms respectively.

Valence Electrons

Electrons in the outermost shell of an atom which interact with similar electrons from another atom leading to bonding.