Carbon and its Compounds

Lesson

Part 1 — why carbon shares electrons, how covalent bonds explain the properties of carbon compounds, and why carbon can form millions of compounds, starting with hydrocarbons.

In this lesson you will

Explain why carbon forms covalent bonds by sharing electrons
Draw electron-dot structures of H2, O2, N2, CH4 and CO2
Explain the low melting points and poor conductivity of covalent compounds
Explain why carbon forms a very large number of compounds
Distinguish alkanes, alkenes and alkynes and draw chains, branches and rings

\ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)}

Methane is the main gas in CNG and in biogas.

Concept

Carbon's problem: four outer electrons

Carbon (atomic number 6) has electronic configuration 2, 4. To reach a stable octet it would have to gain or lose four electrons — both are very difficult. So carbon shares electrons, forming covalent bonds.

Table of carbon’s three options for reaching an octet: gaining or losing four electrons is unfavourable, so carbon shares electrons
Option	Result	Why it does not happen
Gain 4 electrons	C⁴⁻ anion	Six protons cannot hold ten electrons firmly
Lose 4 electrons	C⁴⁺ cation	A very large amount of energy would be needed
Share 4 electrons	Four covalent bonds	This is what carbon does

Diagram

Sharing electrons: hydrogen, oxygen and nitrogen

Dots and crosses show electrons from the two atoms. Single, double and triple bonds have one, two and three shared pairs.

One shared pair makes a single bond, two pairs a double bond, three pairs a triple bond. Non-metals such as hydrogen, oxygen and nitrogen form molecules this way.

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