Polar vs. Nonpolar Covalent Bonds

Covalent Bond: Electrons are shared between atoms.
- Example: Two hydrogen atoms combining to form $H_2$ . The bond represents the sharing of electrons.
Ionic Bond: Electrons are transferred between atoms.
- Example: Sodium (Na) reacting with Chlorine (Cl).
  - Sodium transfers its valence electron to chlorine.
  - Sodium becomes a positive ion (cation) due to the loss of an electron.
  - Chlorine becomes a negative ion (anion) due to the gain of an electron, completing its octet.
  - The electrostatic attraction between the positive and negative ions forms the ionic bond.

Covalent Bonds: Characterized by the electronegativity difference between the bonded atoms.
Nonpolar Covalent Bond: Equal sharing of electrons.
- Example: $H_2$ (hydrogen gas). Both hydrogen atoms have the same electronegativity value (2.1), resulting in equal sharing.
Polar Covalent Bond: Unequal sharing of electrons.
- Example: Hydrogen Fluoride (HF).
  - Fluorine (electronegativity 4.0) is more electronegative than hydrogen (electronegativity 2.1).
  - Fluorine pulls the electrons towards itself, resulting in a partial negative charge ( $\delta^-$ ).
  - Hydrogen develops a partial positive charge ( $\delta^+$ ).
  - This unequal distribution of electrons creates a dipole moment, making the molecule polar.

Ionic Bond:
- Composed of ions (positive and negative charges).
- Typically formed between a metal and a nonmetal.
Covalent Bond:
- Typically formed between two nonmetals.
Polar vs. Nonpolar Covalent Bond:
- Examine the electronegativity difference. A difference of 0.5 or greater indicates a polar covalent bond.

$Cl_2$ (Chlorine molecule):
- Two nonmetals (chlorine atoms) bonded, with the same electronegativity, so it is a nonpolar covalent bond.
C-H (Carbon-Hydrogen bond):
- Both carbon and hydrogen are nonmetals, indicating a covalent bond.
- Electronegativity of carbon is 2.5, and hydrogen is 2.1. The difference is $2.5 - 2.1 = 0.4$ , making it a nonpolar covalent bond.
C-O (Carbon-Oxygen bond):
- Both carbon and oxygen are nonmetals indicating a covalent bond.
- Electronegativity of oxygen is 3.5, and carbon is 2.5. The difference is $3.5 - 2.5 = 1.0$ , indicating a polar covalent bond.
NaF (Sodium Fluoride):
- Sodium is a metal, and fluorine is a nonmetal, suggesting an ionic bond.
- Electronegativity of sodium is 0.93, and fluorine is 4.0. The difference is $4.0 - 0.93 = 3.07$ , confirming it's an ionic bond.

Use the periodic table to gauge electronegativity differences.
The greater the distance between two elements on the periodic table, the larger the electronegativity difference, and the more polar the bond.
Example 1: Comparing N-F, P-F, and As-F bonds.
- Nitrogen (N), Phosphorus (P), and Arsenic (As) are in the same group, with nitrogen being closest to fluorine (F) and arsenic being furthest.
- The arsenic-fluorine bond (As-F) is the most polar because arsenic and fluorine are the farthest apart.
Example 2: Comparing C-F, N-F, and O-F bonds.
- Carbon (C), Nitrogen (N), and Oxygen (O) are in the same period, with carbon being furthest away from fluorine (F) and oxygen being closest.
- The carbon-fluorine bond (C-F) is the most polar because carbon and fluorine are the farthest apart.

O-F bond: Electronegativity difference is $4.0 - 3.5 = 0.5$ , which is a polar covalent bond.
N-F bond: Electronegativity difference is $4.0 - 3.0 = 1.0$ , which is a polar covalent bond.
C-F bond: Electronegativity difference is $4.0 - 2.5 = 1.5$ , which is the most polar bond among the choices.