CARBON AND ITS COMPOUNDS
Class 10 • Exam-Focused Revision Notes •
1. Carbon: Basic Facts and Key Features
Carbon is a non-metal. Atomic number = 6; atomic mass = 12 u; electronic configuration = 2, 4; 4 electrons in the
outer shell; valency = 4.
According to the source, carbon makes up about 0.02% of the Earth's crust and atmospheric CO₂ is about 0.03%.
Carbon-based compounds are found in living organisms and in many substances such as food, clothing, medicines
and fuels.
Carbon forms millions of compounds because of its versatile nature. The main reasons are tetravalency,
catenation, strong covalent bonds and isomerism.
2. Why Does Carbon Form Covalent Compounds Instead of Ionic
Compounds?
Carbon has 4 electrons in its outer shell. To obtain a stable octet, it would have to gain 4 electrons or lose 4
electrons.
If carbon gained 4 electrons, it would have 10 electrons but only 6 protons. This arrangement is considered
unstable for the small carbon atom.
Losing 4 electrons would require a very large amount of energy. Therefore, carbon generally neither gains nor
loses electrons completely.
Instead, carbon atoms share pairs of electrons to form covalent bonds.
Definition: A covalent bond is a chemical bond formed by the mutual sharing of electron pairs between two atoms.
Sharing allows the atoms to attain stable electronic configurations.
EXAM FOCUS: When answering “Why does carbon not form ionic compounds?”, include both reasons: gaining
four electrons would create an unstable arrangement, and losing four electrons would require too much energy.
3. Ionic and Covalent Compounds: Comparison
Property Ionic Compounds Covalent Compounds
Physical state Generally solids May be solids, liquids or gases
Melting/boiling points High Generally low
Weak intermolecular forces between
Reason Strong attraction between ions
molecules
Do not conduct in solid state; conduct Generally poor conductors; free ions are
Electrical conductivity
when molten or in solution absent
May dissolve in water; generally not in Generally soluble in organic solvents and
Solubility
organic solvents insoluble in water
Carbon tetrachloride (CCl₄) is not a good conductor of electricity even though it contains chlorine. It is a covalent
compound and does not contain free ions.
4. Types of Covalent Bonds
Bond Shared electron pairs Shared electrons
Carbon and Its Compounds • Exam-Focused Notes
, Single bond (—) 1 pair 2
Double bond (=) 2 pairs 4
Triple bond (≡) 3 pairs 6
5. Special Properties of Carbon
Property Meaning / Exam-ready point
Carbon forms strong covalent bonds with other carbon atoms,
Catenation
allowing it to make long chains.
Carbon has 4 valence electrons and can form four covalent
Tetravalency
bonds to complete its octet.
Carbon is small, so its nucleus attracts shared electrons strongly;
Strong bonds
this helps it form strong covalent bonds.
Small molecules/monomers join together to form large
Polymerisation
molecules/polymers.
Compounds have the same molecular formula but different
Isomerism
structures; these compounds are called isomers.
6. Allotropes of Carbon
Definition: Allotropes are different physical forms of the same element in which the atoms are arranged differently.
Their physical properties differ, while their chemical properties are described as similar in the source.
Allotrope Structure Main properties Uses / identification
Three-dimensional (3D), Used for cutting glass/rocks
Extremely hard natural
tetrahedral arrangement; each and in jewellery. Artificial
Diamond material; no free electrons, so
carbon is bonded to 4 other diamond can be made under
it does not conduct electricity.
carbon atoms. very high pressure.
Layers slide over one another,
Layers of hexagonal planes;
making graphite soft/slippery;
Graphite each carbon is bonded to 3 Used in pencil “lead”.
free electrons allow it to
other carbon atoms.
conduct electricity.
C₆₀ / buckminsterfullerene; a Uses related to medicines and
The source particularly
Fullerene spherical, football-like nanotechnology/chips are
highlights its spherical shape.
structure. mentioned in the source.
EXAM FOCUS: The structural difference between diamond and graphite explains differences in hardness,
slipperiness and electrical conductivity.
7. Hydrocarbons and Their Classification
Hydrocarbons are compounds containing only carbon and hydrogen.
Saturated hydrocarbons contain C–C single bonds. Unsaturated hydrocarbons contain a double or triple bond.
Class C–C bond Nature General formula
Alkane Single Saturated CₙH₂ₙ₊₂
Alkene At least one double bond Unsaturated CₙH₂ₙ
Alkyne At least one triple bond Unsaturated CₙH₂ₙ₋₂
Examples for n = 2: alkane C₂H₆ (ethane), alkene C₂H₄ (ethene), alkyne C₂H₂ (ethyne).
The first alkane is methane (CH₄). The first members of the alkene and alkyne series are ethene and ethyne,
respectively, because a C–C double or triple bond cannot form with only one carbon atom.
Benzene is an aromatic hydrocarbon with formula C₆H₆. Its structure is shown as a hexagon of six carbon atoms
with three alternating double bonds; each carbon is attached to one hydrogen atom.
Carbon and Its Compounds • Exam-Focused Notes
Class 10 • Exam-Focused Revision Notes •
1. Carbon: Basic Facts and Key Features
Carbon is a non-metal. Atomic number = 6; atomic mass = 12 u; electronic configuration = 2, 4; 4 electrons in the
outer shell; valency = 4.
According to the source, carbon makes up about 0.02% of the Earth's crust and atmospheric CO₂ is about 0.03%.
Carbon-based compounds are found in living organisms and in many substances such as food, clothing, medicines
and fuels.
Carbon forms millions of compounds because of its versatile nature. The main reasons are tetravalency,
catenation, strong covalent bonds and isomerism.
2. Why Does Carbon Form Covalent Compounds Instead of Ionic
Compounds?
Carbon has 4 electrons in its outer shell. To obtain a stable octet, it would have to gain 4 electrons or lose 4
electrons.
If carbon gained 4 electrons, it would have 10 electrons but only 6 protons. This arrangement is considered
unstable for the small carbon atom.
Losing 4 electrons would require a very large amount of energy. Therefore, carbon generally neither gains nor
loses electrons completely.
Instead, carbon atoms share pairs of electrons to form covalent bonds.
Definition: A covalent bond is a chemical bond formed by the mutual sharing of electron pairs between two atoms.
Sharing allows the atoms to attain stable electronic configurations.
EXAM FOCUS: When answering “Why does carbon not form ionic compounds?”, include both reasons: gaining
four electrons would create an unstable arrangement, and losing four electrons would require too much energy.
3. Ionic and Covalent Compounds: Comparison
Property Ionic Compounds Covalent Compounds
Physical state Generally solids May be solids, liquids or gases
Melting/boiling points High Generally low
Weak intermolecular forces between
Reason Strong attraction between ions
molecules
Do not conduct in solid state; conduct Generally poor conductors; free ions are
Electrical conductivity
when molten or in solution absent
May dissolve in water; generally not in Generally soluble in organic solvents and
Solubility
organic solvents insoluble in water
Carbon tetrachloride (CCl₄) is not a good conductor of electricity even though it contains chlorine. It is a covalent
compound and does not contain free ions.
4. Types of Covalent Bonds
Bond Shared electron pairs Shared electrons
Carbon and Its Compounds • Exam-Focused Notes
, Single bond (—) 1 pair 2
Double bond (=) 2 pairs 4
Triple bond (≡) 3 pairs 6
5. Special Properties of Carbon
Property Meaning / Exam-ready point
Carbon forms strong covalent bonds with other carbon atoms,
Catenation
allowing it to make long chains.
Carbon has 4 valence electrons and can form four covalent
Tetravalency
bonds to complete its octet.
Carbon is small, so its nucleus attracts shared electrons strongly;
Strong bonds
this helps it form strong covalent bonds.
Small molecules/monomers join together to form large
Polymerisation
molecules/polymers.
Compounds have the same molecular formula but different
Isomerism
structures; these compounds are called isomers.
6. Allotropes of Carbon
Definition: Allotropes are different physical forms of the same element in which the atoms are arranged differently.
Their physical properties differ, while their chemical properties are described as similar in the source.
Allotrope Structure Main properties Uses / identification
Three-dimensional (3D), Used for cutting glass/rocks
Extremely hard natural
tetrahedral arrangement; each and in jewellery. Artificial
Diamond material; no free electrons, so
carbon is bonded to 4 other diamond can be made under
it does not conduct electricity.
carbon atoms. very high pressure.
Layers slide over one another,
Layers of hexagonal planes;
making graphite soft/slippery;
Graphite each carbon is bonded to 3 Used in pencil “lead”.
free electrons allow it to
other carbon atoms.
conduct electricity.
C₆₀ / buckminsterfullerene; a Uses related to medicines and
The source particularly
Fullerene spherical, football-like nanotechnology/chips are
highlights its spherical shape.
structure. mentioned in the source.
EXAM FOCUS: The structural difference between diamond and graphite explains differences in hardness,
slipperiness and electrical conductivity.
7. Hydrocarbons and Their Classification
Hydrocarbons are compounds containing only carbon and hydrogen.
Saturated hydrocarbons contain C–C single bonds. Unsaturated hydrocarbons contain a double or triple bond.
Class C–C bond Nature General formula
Alkane Single Saturated CₙH₂ₙ₊₂
Alkene At least one double bond Unsaturated CₙH₂ₙ
Alkyne At least one triple bond Unsaturated CₙH₂ₙ₋₂
Examples for n = 2: alkane C₂H₆ (ethane), alkene C₂H₄ (ethene), alkyne C₂H₂ (ethyne).
The first alkane is methane (CH₄). The first members of the alkene and alkyne series are ethene and ethyne,
respectively, because a C–C double or triple bond cannot form with only one carbon atom.
Benzene is an aromatic hydrocarbon with formula C₆H₆. Its structure is shown as a hexagon of six carbon atoms
with three alternating double bonds; each carbon is attached to one hydrogen atom.
Carbon and Its Compounds • Exam-Focused Notes
