Ionic and Covalent Bonding - Chemistry

Main Ideas

• Ionic bonds usually form between a metal and a nonmetal. Electrons are transferred, producing positively and negatively charged ions. The attraction between these opposite charges holds the ions together.
• Covalent bonds usually form between two nonmetals, which share electrons.
• Covalent bonds can be:
  • Nonpolar covalent: Electrons are shared equally or nearly equally, so there is little or no separation of charge.
  • Polar covalent: Electrons are shared unequally. The atom that attracts electrons more strongly becomes partially negative, while the other becomes partially positive. The molecule remains neutral overall.
• Electronegativity difference can help estimate whether a covalent bond is polar:
  • A difference of 0.5 or more is described in the video as polar covalent.
  • A difference of 0.4 or less is described as nonpolar covalent.
• The periodic table helps identify metals and nonmetals. Metals are generally to the left of the dividing line, nonmetals to the right, and elements near the line are often metalloids. Hydrogen is an exception: despite its position, it is treated as a nonmetal.

How to Classify a Bond

1. Identify the elements in the bond.
2. Determine whether they are metals or nonmetals using the periodic table:
   • A metal and a nonmetal usually form an ionic bond.
   • Two nonmetals usually form a covalent bond.
3. If the bond is covalent, compare the atoms’ electronegativities:
   • Identical elements have an electronegativity difference of zero and form a nonpolar covalent bond.
   • A small difference indicates nonpolar covalent character; a larger difference indicates polar covalent character.
4. Keep in mind that these are general rules, not absolutes. Some compounds contain both ionic and covalent bonds.

Examples

• Br₂ (bromine): Two identical nonmetal atoms share electrons equally, forming a nonpolar covalent bond. Each atom contributes one electron to the shared pair and completes an octet.
• C–H in methane (CH₄): Carbon and hydrogen are both treated as nonmetals. Their electronegativity difference is about 0.4, so the bond is classified as nonpolar covalent in the video.
• C–O: Both elements are nonmetals, so the bond is covalent. The stated electronegativity difference is 1.0, making it polar covalent. Oxygen attracts the shared electrons more strongly and becomes partially negative; carbon becomes partially positive.
• LiF (lithium fluoride): Lithium is a metal and fluorine is a nonmetal. Lithium transfers an electron to fluorine, forming oppositely charged ions and an ionic bond.
• Ammonium nitrate (NH₄NO₃): This is an exception to the simple metal/nonmetal rule. It contains an ionic attraction between the ammonium ion (NH₄⁺) and nitrate ion (NO₃⁻), while the bonds within each polyatomic ion are covalent. The N–H and N–O bonds are described as polar covalent.

Speakers and Sources

• Speaker: One unnamed instructor or narrator.
• Sources and references: The periodic table and electronegativity values. The narrator also suggests searching Google Images for periodic-table and electronegativity charts. No other speakers are identified.