1.1 Explain the occurrence of carbon compounds with straight chains, branched chains and rings.

MODULE 1. THE CHEMISTRY OF CARBON COMPOUNDS

Learning Outcomes

TOPIC: BONDING IN CARBON COMPOUNDS

Carbon forms many more compounds than any other element. This is partly because, once formed, the carbon to carbon (C- C) single covalent bonds are very strong in comparison to other single covalent bonds.

It takes a lot of energy to break these strong bonds, so the compounds form are stable.

The ability of carbon atoms to form chains or rings compounds by joining together is called CATENATION.

Carbon-carbon bonds are also non-polar, and this helps to reduce their vulnerability by other chemicals.

BONDING IN CARBON COMPOUNDS

Carbon atom:

is tetravalenttetravalent

has the ability to bond with other

carbon atoms to form straight chains,

branches and ring compounds. This is

known as catenation.catenation.

has the ability to mix and rearrange the

four orbitals in the outer shell

(hybridizationhybridization) e.g. sp3, sp2, sp.

has resonance (delocalized electrons)

WHY CARBON IS THE UNIQUE THAT WHY CARBON IS THE UNIQUE THAT IT FORMS A LARGE VARIETY OF IT FORMS A LARGE VARIETY OF

COMPOUNDS?COMPOUNDS?

Carbon atoms are able to form a few types of

covalent bonds covalent bonds with other carbon atoms or

atoms of other elements:

Single bonds: C-C, C-H, C-O, C-X

(X = halogens)

Double bonds: C=C, C=O

Triple bonds: C≡ C, C≡N

Organic compounds can be classified as

unbranched, branched or ring compounds.

Straight-chain molecules that are unbranched may contain single, double or triple bonds. E.g.:

Straight (unbranched) Chain Compounds

Single bond Double bonds

Triple bonds

Branched- Chain CompoundsBranched chain

compounds consist of one or more carbons of a straight chain compound forming bonds with more than two carbons.

Ring Chain Compounds

• Ring chain compounds consist of a ring of carbon atoms

There are five types of formulae which can be used to describe and identify organic compounds:

Hybridisation in Carbon Compounds

Carbon is in Group IV of the Periodic Table. This means that it has 4 electrons in its outer principle quantum shell., which are able to form bonds with other atoms. It exhibits TETRAVALENCY.

A covalent bond is formed by sharing of two electrons, one from each atom. Carbon can form four bonds because one of the 2s electrons in the carbon atom is transferred to a 2p orbital to give the four unpaired electrons necessary for forming four bonds.

The process of mixing atomic orbitals is called HYBRIDIZATION

Hybridisation in Carbon Compounds

Hybridisation in Carbon Compounds

Hybridisation in Carbon Compounds

Resonance

In ethane and ethene the electrons are localised. In some substances, the molecular orbitals extend over three or more atoms, allowing the electrons free movement over these atoms. These electrons are said to be delocalised.

Benzene (C6H6) has 6 carbon atoms arranged in a ring. The bonds between the carbon atoms are neither double nor single bonds. They are somewhere in between. Making up a composite structure from several different structures is called mesomerism. The composite structure is called a resonance hybrid.

ResonanceResonance arises whenever we can write two

or more structures for a molecule with different arrangements of the electrons but identical arrangements of atoms.

When resonance is possible, the substance that is a resonance is said to have a structure that is a resonance hybrid of the various contributing structures.

Resonance in Benzene

Compounds such as benzene, which have this delocalised electron ring structure are called aryl compounds.

Key Points A large number of carbon compounds are

formed by catenation- the joining of carbon atoms together to form straight or branched chains of atoms or ring compounds.

Most organic compounds are stable because of the high value of the C-C bond energy and the non-polar nature of this bond.

Hybridisation of s and p orbitals results in the formation of an orbital with mixed character.

Resonance is where the structure of a compound is a single form which is “in-between” two or more structures.

Explain the characteristic of

compounds which belongs to the

same homologous series.

Homework