Question

Write a Lewis formula for each of the following: (a) \(\mathrm{HCN}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{2}\) (e) \(\mathrm{C}_{2} \mathrm{H}_{6}\) (b) \(\mathrm{H}_{3} \mathrm{CCN}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{4}\)

Short answer

The Lewis structures for \(\mathrm{HCN}\), \(\mathrm{C}_{2} \mathrm{H}_{2}\), \(\mathrm{C}_{2} \mathrm{H}_{6}\), \(\mathrm{H}_{3} \mathrm{CCN}\), and \(\mathrm{C}_{2} \mathrm{H}_{4}\) are H:C:::N:, H:C:::C:H, H3C-CH3, H3C-CH2:::N:, and H2C=CH2 respectively.

Step-by-step solution

Lewis Structure for \(\mathrm{HCN}\)

Hydrogen(H) has 1 electron, Carbon(C) has 4 and Nitrogen(N) has 5. The C is the central atom. The total no. of valence electrons is 10. The bonds are H-C and C≡N. Therefore the Lewis structure is H:C:::N:.

Lewis Structure for \(\mathrm{C}_{2} \mathrm{H}_{2}\)

Each Carbon (C) atom has 4 electrons and each Hydrogen (H) atom has 1 electron. The total no. of valence electrons is 10. The bonds are C≡C and each C-H. Therefore, the Lewis structure is H:C:::C:H.

Lewis Structure for \(\mathrm{C}_{2} \mathrm{H}_{6}\)

Each Carbon (C) atom has 4 electrons and each Hydrogen (H) atom has 1 electron. The total no. of valence electrons is 14. The bonds are C-C and each C-H. Therefore, the Lewis structure is H3C-CH3.

Lewis Structure for \(\mathrm{H}_{3} \mathrm{CCN}\)

Each Carbon (C) atom has 4 electrons, Nitrogen has 5 electrons, and each Hydrogen (H) atom has 1 electron. The total no. of valence electrons is 14. The bonds are C-C, N:::C, and each C-H. Therefore, the Lewis structure is H3C-CH2:::N:.

Lewis Structure for \(\mathrm{C}_{2} \mathrm{H}_{4}\)

Each Carbon (C) atom has 4 electrons and each Hydrogen (H) atom has 1 electron. The total no. of valence electrons is 12. The bonds are C=C and each C-H. Therefore, the Lewis structure is H2C=CH2.

Key concepts

Valence Electrons

Valence electrons are crucial in understanding Lewis structures as they are the outermost electrons of an atom participating in chemical bonding. When looking at an element's position on the periodic table, you'll find valence electrons in the s and p orbitals of the highest energy level. These electrons determine how atoms interact with each other to form molecules. For instance, in the molecule \(\mathrm{HCN}\), hydrogen has one valence electron, carbon has four, and nitrogen has five. Together, these sum to a total of 10 valence electrons for forming the structure.

• Hydrogen atoms are simple with only one valence electron.
• Carbon is tetravalent with four electrons available for bonding.
• Nitrogen typically forms three bonds given its five valence electrons.

Knowing how to count and allocate these electrons appropriately is key in drawing correct Lewis structures. This allocation helps ensure that all bonding elements satisfy the octet rule where applicable, leading to stable electron arrangements.

Chemical Bonding

Chemical bonding is the force that holds atoms together within molecules. There are several types of bonds, but the most important ones for Lewis structures are covalent bonds, where atoms share electrons to achieve stable electron configurations. In \(\mathrm{C_2H_2}\) (acetylene), each carbon shares three electron pairs with each other, forming a triple bond (C≡C).

• Single Bond: In a single bond, atoms share one pair of electrons. For instance, in \(\mathrm{C_2H_6}\) (ethane), each hydrogen forms a single bond with carbon.
• Double Bond: Two shared pairs of electrons as in \(\mathrm{C_2H_4}\) (ethylene) with a C=C bond.
• Triple Bond: Three pairs of electrons shared, such as in \(\mathrm{HCN}\) or \(\mathrm{C_2H_2}\), shown by the C≡N or C≡C bonds respectively.

Chemical bonding is fundamental, allowing molecules to form and maintaining their structure, clearly depicted in their electron sharing schemes in Lewis structures.

Organic Compounds

Organic compounds primarily consist of carbon atoms bonded to hydrogen, oxygen, nitrogen, and other elements. Their versatility in forming various types of bonds makes organic chemistry fascinating and complex. In the given examples, hydrocarbons such as \(\mathrm{C_2H_6}\) (ethane) and \(\mathrm{C_2H_4}\) (ethylene) illustrate typical organic compounds.

• Hydrocarbons: Compounds consisting entirely of carbon and hydrogen.
  • Alkanes like \(\mathrm{C_2H_6}\) are characterized by single C-C bonds.
  • Alkenes such as \(\mathrm{C_2H_4}\) feature one or more double bonds.
  • Alkynes like \(\mathrm{C_2H_2}\) contain carbon-carbon triple bonds.
• Functional groups: These are specific groups of atoms that impart distinct chemical and physical properties to molecules.
  • Alcohols, ketones, and acids are examples of organic compounds with specialized functions.

Understanding the structure and bonding in organic compounds is vital for recognizing the vast array of chemical reactions they can participate in. The diversity of organic compounds is largely due to carbon's ability to form multiple bonds and stable structures.