Carbon and its Compounds

Introduction

Carbon is a unique and versatile element that forms the basis of all known life on Earth. It is the foundation of organic chemistry due to its ability to form a vast number of compounds, more than any other element. Despite its relatively small abundance in the Earth's crust (about 0.02% in minerals such as carbonates, hydrogen-carbonates, coal, and petroleum) and in the atmosphere (about 0.03% as carbon dioxide), carbon's importance is immense. This chapter explores the properties of carbon that make it so significant, both in its elemental form and in its compounds. The chapter begins by engaging students in an activity to list items they use daily and classifying them by material, highlighting that many items are made of carbon compounds. It also introduces the idea that burning carbon compounds produces carbon dioxide, which can be tested to confirm the presence of carbon. The chapter sets the stage for understanding the bonding, structure, and chemical behavior of carbon compounds, which are fundamental to living organisms and many materials around us. **Table on page 1 (2×3)** | Things made of metal | Things made of glass/clay | Others | | --- | --- | --- | | | | | **Table on page 2 (5×3)** | Compound | Melting point (K) | Boiling point (K) | | --- | --- | --- | | Acetic acid (CH2COOH) | 290 | 391 | | Chloroform (CHCl3) | 209 | 334 | | Ethanol (CH2CH2OH) | 156 | 351 | | Methane (CH4) | 90 | 111 | **Table on page 11 (4×1)** | Q U E S T I O N S | | --- | | 1. How many structural isomers can you draw for pentane? | | 2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us? | | 3. What will be the formula and electron dot structure of cyclopentane? | **Table on page 14 (3×1)** | QUESTIONS | | --- | | 1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction? | | 2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used? |

• Carbon forms the basis of all known life and organic chemistry.
• It is found in more compounds than any other element.
• Carbon is present in small amounts in the Earth's crust and atmosphere.
• Many everyday items are made of carbon compounds.
• Burning carbon compounds produces carbon dioxide, a test for carbon presence.
• 📌 Carbon: An element with atomic number 6, fundamental to organic chemistry.
• 📌 Carbon compounds: Chemical compounds containing carbon atoms.
• 📌 Carbon dioxide (CO2): A gas produced when carbon compounds burn.

4.1 BONDING IN CARBON – THE COVALENT BOND

This section explains the nature of bonding in carbon compounds, focusing on covalent bonds. Unlike ionic compounds, which have high melting and boiling points and conduct electricity in molten or solution states, most carbon compounds have low melting and boiling points and are poor conductors of electricity. This indicates that the forces between their molecules are weak and that bonding does not involve ions. Carbon has an atomic number of 6, with four electrons in its outermost shell. To attain a stable noble gas configuration, carbon needs to gain or lose four electrons, which is energetically unfavorable. Instead, carbon shares its four valence electrons with other atoms, forming covalent bonds. The shared electrons belong to the outermost shells of both atoms, allowing them to achieve noble gas configurations. Examples include hydrogen molecules (H2) formed by sharing one electron each, chlorine molecules (Cl2), oxygen molecules (O2) with double bonds, and nitrogen molecules (N2) with triple bonds. Methane (CH4) is introduced as a simple carbon compound where carbon shares electrons with four hydrogen atoms, forming four single covalent bonds. Covalent bonds are strong within molecules but intermolecular forces are weak, explaining the physical properties of carbon compounds. Since no ions are formed, these compounds do not conduct electricity.

• Carbon compounds generally have covalent bonds, not ionic bonds.
• Carbon has four valence electrons and forms four covalent bonds to complete its octet.
• Covalent bonds involve sharing electron pairs between atoms.
• Single, double, and triple covalent bonds exist depending on the number of shared electron pairs.
• Methane (CH4) is a simple example of a carbon compound with four single covalent bonds.
• Covalent compounds have low melting/boiling points and do not conduct electricity.
• 📌 Covalent bond: A bond formed by sharing a pair of electrons between two atoms.
• 📌 Valence electrons: Electrons in the outermost shell of an atom.
• 📌 Octet rule: Atoms tend to attain eight electrons in their outer shell for stability.