4.5 Electrostatic Attraction in Covalent Bonding

Electrostatic Attraction in Covalent Bonding

4.5.1 Covalent Bonding

• Definition of Covalent Bonding: Covalent bonding involves the sharing of electrons between atoms, specifically non-metal atoms.

• Ionic vs. Covalent Bonding: Ionic compounds form through the transfer of electrons from metal to non-metal atoms. However, covalent bonding occurs when two non-metal atoms share electrons to achieve stability.

• Electrostatic Attraction: The essence of covalent bonding is the electrostatic attraction between positively charged nuclei of atoms and the negatively charged electrons they share.

• Examples of Covalent Compounds: Examples include
    - Water ($H_2O$)
    - Carbon dioxide ($CO_2$)
    - Diamond ($C$)
    - Quartz ($SiO_2$)

• Types of Molecules: Molecules can consist of the same type of atoms (e.g., oxygen gas, $O_2$) or different types of atoms (e.g., water, $H_2O$).

• Stability through Electron Sharing: Sharing electrons helps each atom achieve a stable electron configuration, allowing the fulfillment of the octet rule for most elements or the duet rule for hydrogen.

4.5.2 Covalent Bonding in Water

• Covalent Bonds in Water: In $H_2O$, each hydrogen atom forms a covalent bond with the oxygen atom through electron sharing.
    - Valence Electrons: Hydrogen has 1 valence electron, and oxygen has 6 valence electrons.
    - Total Electrons in Bonds: Each hydrogen atom contributes 1 electron to the bond with oxygen, resulting in hydrogen having 2 electrons (duet) and oxygen achieving 8 electrons (octet).

• Octet Rule: Atoms must fulfill the octet rule (8 electrons in the outer shell), while hydrogen follows the duet rule with only 2 electrons needed for stability.

4.5.2 Electron Dots: What’s the Point?

• Electron Dot Diagrams: Also known as Lewis structures, these diagrams illustrate the distribution of valence electrons in atoms and molecules. They are essential for visualizing how atoms bond.

• Creating Electron Dot Diagrams for Atoms:
    1. Draw the element symbol.
    2. Determine the number of outer (valence) shell electrons (often corresponds to the group number in the periodic table).
    3. Add one electron to each of four regions surrounding the symbol until all electrons are assigned or all regions are filled.
    4. Pair any remaining electrons.

4.5.3 Using Electron Dot Diagrams for Molecules

• Combining Elements: When elements form covalent compounds, sharing electrons helps them achieve stable outer shells via the octet rule, while hydrogen adheres to the duet rule.

• Structural Formulas: A structural formula can be drawn using dashes to represent covalent bonds, with non-bonding electrons omitted.

• Types of Covalent Bonds:
    - Single Covalent Bond: One pair of electrons shared.
    - Double Covalent Bond: Two pairs of electrons shared (e.g., $O_2$).
    - Triple Covalent Bond: Three pairs of electrons shared (e.g., $N_2$).

• Drawing Electron Dot Diagrams for Molecules:
    1. Identify the atom that will form the most bonds, placing it at the center.
    2. Arrange surrounding atoms next to this central atom.
    3. Assign the necessary number of valence electrons for each atom based on bonding requirements.
    4. Add a pair of electrons (bonding electrons) between atoms forming covalent bonds.
    5. Identify and add non-bonding pairs as necessary.
    6. Ensure that all atoms satisfy their octet or duet rule, confirming valence electrons are fully accounted for.

4.5.4 Properties of Covalent Compounds

• Common Properties of Covalent Compounds:
    - Physical states: Exist as gases, liquids, or solids with low melting points due to weak intermolecular forces.
    - Electrical conductivity: Cannot conduct electricity as they do not contain ions.

4.5.5 Formation of Covalent Molecules with Single Covalent Bonds

• Examples of Covalent Compounds:
    - Chlorine ($Cl_2$): Each chlorine atom shares one electron, achieving a stable outer shell of 8 electrons.
    - Hydrogen Chloride ($HCl$): Both hydrogen and chlorine share one electron.
    - Water ($H_2O$): Each hydrogen shares one electron, while oxygen shares two to stabilize.

4.5.6 Double and Triple Covalent Bonds

• Examples of Double and Triple Covalent Bonds:
    - Oxygen ($O_2$): Each oxygen shares two electrons (double bond).
    - Nitrogen ($N_2$): Each nitrogen shares three electrons (triple bond).
    - Carbon Dioxide ($CO_2$): Each oxygen requires two electrons and carbon four for stability.

4.5.7 Discussions on Antioxidants

• Antioxidants: Chemicals that prevent damage to vital molecules such as DNA by neutralizing oxygen radicals, which have unpaired electrons and are highly reactive.

• Oxygen Radicals and Safety: The reactivity of oxygen radicals in biological processes raises the question of why such radicals occur in our body yet molecular oxygen ($O_2$) is essential for life at 21% concentration in the atmosphere.

Figures and Tables

• Figures: The various figures illustrating concepts in covalent bonding provide visual references.
    - Figure 4.37: Electrostatic attraction in a covalent bond
    - Figure 4.38: Formation of covalent bonds in water
    - Figure 4.39 & 4.40: Examples of covalent molecules and network lattices.

• Tables:
    - Table 4.13: Electron dot diagrams for elements (H, C, O, F)
    - Table 4.14: Formation of covalent molecules with single covalent bonds
    - Table 4.15: Formation of double and triple covalent bonds.