CARBON AND ITS COMPOUNDS
DEEP EXPLANATION • CONCEPTS • REACTIONS • IUPAC NAMING • EXAM PRACTICE
These expanded notes explain the concepts step by step and include worked examples. They follow the topics and
framing of the lecture notes; examples are used to make the ideas easier to understand.
1. Carbon: The Basic Idea
Carbon is a non-metal with atomic number 6. Its electronic configuration is 2,4: two electrons occupy the first shell
and four occupy the outermost shell. The four outer-shell electrons are called valence electrons, so carbon has
valency 4.
A stable outer shell for carbon is associated with eight electrons. Carbon has four already, so it would need four
more to complete an octet. Rather than completely gaining or losing four electrons, carbon usually shares
electrons with other atoms. This sharing creates covalent bonds.
Fact Meaning
Atomic number = 6 A neutral carbon atom has 6 protons and 6 electrons.
Electronic configuration = 2,4 There are 4 electrons in the outermost shell.
Valency = 4 Carbon can form four covalent bonds in common compounds.
Atomic mass ≈ 12 u The approximate mass used in the notes for carbon.
Why is carbon so important? Carbon atoms can bond to other carbon atoms and to atoms such as hydrogen,
oxygen, chlorine and others. As a result, carbon can form many different chains, branches, rings and functional
groups. This ability underlies the huge variety of carbon compounds.
2. Why Carbon Usually Forms Covalent Bonds
An ionic bond generally forms when electrons are transferred from one atom to another. Carbon has four valence
electrons, so two extreme possibilities would be to gain four electrons or lose four electrons.
If carbon gained four electrons, it would become a negatively charged ion with ten electrons but only six protons. If
it lost four electrons, it would form a positively charged ion and the removal of four electrons would require a very
large amount of energy. The lecture therefore explains that neither complete gain nor complete loss is favourable
for carbon.
Instead, carbon shares electron pairs. A shared pair counts toward the outer shell of both bonded atoms. The
resulting bond is called a covalent bond.
Example: In methane, CH₄, one carbon atom shares one pair of electrons with each of four hydrogen atoms. Each
hydrogen gets access to two electrons (a duplet), while carbon gets access to eight electrons (an octet).
Carbon + 4 hydrogen atoms → CH₄ (methane)
Exam-ready answer: Carbon generally forms covalent compounds because gaining four electrons would produce
an unstable arrangement, while losing four electrons requires too much energy. Sharing electrons allows carbon to
complete its octet.
3. Ionic Compounds vs Covalent Compounds
In ionic compounds, electrons are transferred and oppositely charged ions attract one another. In covalent
compounds, atoms share electron pairs and form molecules. This difference in bonding helps explain their
properties.
Carbon and Its Compounds • Deep English Notes
, Property Ionic compounds Covalent compounds
Positive and negative ions held by Atoms share electron pairs to form
Particles / bonding
electrostatic attraction molecules
Often high because strong attractions Often lower because the forces between
Melting and boiling points
between ions must be overcome separate molecules are comparatively weak
Conduct when molten or dissolved if ions
Usually poor conductors because they do
Electrical conduction can move; usually not as solids because
not contain mobile ions
ions are fixed
Many dissolve in water; behaviour depends Many dissolve in organic solvents;
Solubility
on the compound behaviour depends on the compound
Carbon tetrachloride (CCl₄) contains covalent bonds. It does not contain freely moving ions, so it is a poor
conductor of electricity. Do not assume that a compound containing chlorine must be ionic: the type of bonding
depends on the atoms and the way electrons are used.
Important wording: ‘Generally’ or ‘often’ is safer than claiming every ionic or covalent compound has exactly the
same physical properties.
4. Single, Double and Triple Covalent Bonds
A covalent bond consists of one or more shared electron pairs between atoms.
Bond type Notation Shared pairs Shared electrons Example
Single C–C 1 2 Ethane, C₂H₆
Double C=C 2 4 Ethene, C₂H₄
Triple C≡C 3 6 Ethyne, C₂H₂
A line in a structural formula represents one shared pair. Thus, two lines represent two shared pairs, and three
lines represent three shared pairs. The type of carbon–carbon bond is central to classifying hydrocarbons as
saturated or unsaturated.
5. The Four Key Ideas Behind Carbon's Versatility
5.1 Tetravalency
Tetra means four. Carbon has four valence electrons and commonly forms four covalent bonds. For example, in
CH₄, carbon forms four C–H single bonds. In ethane, each carbon forms one C–C bond and three C–H bonds,
giving each carbon a total of four bonds.
5.2 Catenation
Catenation is the ability of an element to bond with atoms of the same element. Carbon forms strong C–C bonds,
so carbon atoms can join into straight chains, branched chains and rings. The carbon skeleton can contain many
atoms, allowing a large variety of structures.
5.3 Strong covalent bonds
Carbon atoms are relatively small, allowing strong attraction between their nuclei and shared electrons. Strong
carbon–carbon bonds help chains and rings remain stable.
5.4 Isomerism
Two compounds can have the same molecular formula but different arrangements of atoms. These are called
isomers. Since the atoms are connected differently, the compounds may have different properties. For example,
C₄H₁₀ can form a straight chain (butane) or a branched structure (isobutane).
Carbon and Its Compounds • Deep English Notes
DEEP EXPLANATION • CONCEPTS • REACTIONS • IUPAC NAMING • EXAM PRACTICE
These expanded notes explain the concepts step by step and include worked examples. They follow the topics and
framing of the lecture notes; examples are used to make the ideas easier to understand.
1. Carbon: The Basic Idea
Carbon is a non-metal with atomic number 6. Its electronic configuration is 2,4: two electrons occupy the first shell
and four occupy the outermost shell. The four outer-shell electrons are called valence electrons, so carbon has
valency 4.
A stable outer shell for carbon is associated with eight electrons. Carbon has four already, so it would need four
more to complete an octet. Rather than completely gaining or losing four electrons, carbon usually shares
electrons with other atoms. This sharing creates covalent bonds.
Fact Meaning
Atomic number = 6 A neutral carbon atom has 6 protons and 6 electrons.
Electronic configuration = 2,4 There are 4 electrons in the outermost shell.
Valency = 4 Carbon can form four covalent bonds in common compounds.
Atomic mass ≈ 12 u The approximate mass used in the notes for carbon.
Why is carbon so important? Carbon atoms can bond to other carbon atoms and to atoms such as hydrogen,
oxygen, chlorine and others. As a result, carbon can form many different chains, branches, rings and functional
groups. This ability underlies the huge variety of carbon compounds.
2. Why Carbon Usually Forms Covalent Bonds
An ionic bond generally forms when electrons are transferred from one atom to another. Carbon has four valence
electrons, so two extreme possibilities would be to gain four electrons or lose four electrons.
If carbon gained four electrons, it would become a negatively charged ion with ten electrons but only six protons. If
it lost four electrons, it would form a positively charged ion and the removal of four electrons would require a very
large amount of energy. The lecture therefore explains that neither complete gain nor complete loss is favourable
for carbon.
Instead, carbon shares electron pairs. A shared pair counts toward the outer shell of both bonded atoms. The
resulting bond is called a covalent bond.
Example: In methane, CH₄, one carbon atom shares one pair of electrons with each of four hydrogen atoms. Each
hydrogen gets access to two electrons (a duplet), while carbon gets access to eight electrons (an octet).
Carbon + 4 hydrogen atoms → CH₄ (methane)
Exam-ready answer: Carbon generally forms covalent compounds because gaining four electrons would produce
an unstable arrangement, while losing four electrons requires too much energy. Sharing electrons allows carbon to
complete its octet.
3. Ionic Compounds vs Covalent Compounds
In ionic compounds, electrons are transferred and oppositely charged ions attract one another. In covalent
compounds, atoms share electron pairs and form molecules. This difference in bonding helps explain their
properties.
Carbon and Its Compounds • Deep English Notes
, Property Ionic compounds Covalent compounds
Positive and negative ions held by Atoms share electron pairs to form
Particles / bonding
electrostatic attraction molecules
Often high because strong attractions Often lower because the forces between
Melting and boiling points
between ions must be overcome separate molecules are comparatively weak
Conduct when molten or dissolved if ions
Usually poor conductors because they do
Electrical conduction can move; usually not as solids because
not contain mobile ions
ions are fixed
Many dissolve in water; behaviour depends Many dissolve in organic solvents;
Solubility
on the compound behaviour depends on the compound
Carbon tetrachloride (CCl₄) contains covalent bonds. It does not contain freely moving ions, so it is a poor
conductor of electricity. Do not assume that a compound containing chlorine must be ionic: the type of bonding
depends on the atoms and the way electrons are used.
Important wording: ‘Generally’ or ‘often’ is safer than claiming every ionic or covalent compound has exactly the
same physical properties.
4. Single, Double and Triple Covalent Bonds
A covalent bond consists of one or more shared electron pairs between atoms.
Bond type Notation Shared pairs Shared electrons Example
Single C–C 1 2 Ethane, C₂H₆
Double C=C 2 4 Ethene, C₂H₄
Triple C≡C 3 6 Ethyne, C₂H₂
A line in a structural formula represents one shared pair. Thus, two lines represent two shared pairs, and three
lines represent three shared pairs. The type of carbon–carbon bond is central to classifying hydrocarbons as
saturated or unsaturated.
5. The Four Key Ideas Behind Carbon's Versatility
5.1 Tetravalency
Tetra means four. Carbon has four valence electrons and commonly forms four covalent bonds. For example, in
CH₄, carbon forms four C–H single bonds. In ethane, each carbon forms one C–C bond and three C–H bonds,
giving each carbon a total of four bonds.
5.2 Catenation
Catenation is the ability of an element to bond with atoms of the same element. Carbon forms strong C–C bonds,
so carbon atoms can join into straight chains, branched chains and rings. The carbon skeleton can contain many
atoms, allowing a large variety of structures.
5.3 Strong covalent bonds
Carbon atoms are relatively small, allowing strong attraction between their nuclei and shared electrons. Strong
carbon–carbon bonds help chains and rings remain stable.
5.4 Isomerism
Two compounds can have the same molecular formula but different arrangements of atoms. These are called
isomers. Since the atoms are connected differently, the compounds may have different properties. For example,
C₄H₁₀ can form a straight chain (butane) or a branched structure (isobutane).
Carbon and Its Compounds • Deep English Notes
