Chemical Bonds: Covalent vs. Ionic

Summary

Mr. Anderson explains how to distinguish nonpolar covalent, polar covalent, and ionic bonds by comparing the electronegativities of the atoms involved.

Bond Types

• Covalent bonds form when atoms share electrons.
  • Nonpolar covalent: Electrons are shared relatively equally.
  • Polar covalent: Electrons are shared unequally, so one atom attracts them more strongly.
• Ionic bonds form when electrons transfer from one atom to another. The resulting oppositely charged ions attract.
• Metallic bonds are briefly mentioned but not explored. In metals, electrons are shared collectively, contributing to properties such as conductivity and hardness.

Octet Rule and Electronegativity

• The octet rule is presented as a useful model: atoms tend to gain, lose, or share electrons to achieve a full outer electron shell, often eight electrons.
• Electronegativity measures how strongly an atom attracts electrons.
• In general, electronegativity increases across a period from left to right and up a group on the periodic table. Fluorine is identified as the most electronegative element.

Method for Classifying a Bond

1. Look up the electronegativity of each atom on the periodic table.
2. Subtract the lower value from the higher value to find the electronegativity difference.
3. Use the video’s approximate ranges:
   • 0 to 0.5: Nonpolar covalent
   • 0.5 to 1.7: Polar covalent
   • Greater than 1.7: Ionic

The video notes that precise cutoffs can vary by source.

Examples

• Water (O–H): Oxygen is 3.44 and hydrogen is 2.20. The difference is 1.24, so the bonds are polar covalent.
• Diesel fuel (C–H): Carbon is 2.55 and hydrogen is 2.20. The difference is 0.35, so the bonds are nonpolar covalent. The video contrasts nonpolar diesel with polar water to explain why they do not mix: “like attracts like.”
• Salt (Na–Cl): Sodium is 0.93 and chlorine is 3.16. The difference is 2.23, so the bond is ionic. Sodium transfers an electron to chlorine, forming oppositely charged ions that attract.
• Ammonia (N–H): Nitrogen is 3.04 and hydrogen is 2.20. The difference is 0.84, so the N–H bonds are polar covalent.

Speakers and Sources

• Speaker: Mr. Anderson, the video’s narrator and instructor.
• Reference source: A periodic table, used to look up electronegativity values.