Introduction to Ionic Bonding and Covalent Bonding

Summary

The video explains how ionic and covalent bonds differ, then presents a method for classifying bonds based on the elements involved and their electronegativity values.

Ionic bonding

• In an ionic bond, electrons are transferred from one atom to another.
• Metals tend to lose electrons and become positively charged ions. Nonmetals tend to gain electrons and become negatively charged ions.
• The oppositely charged ions attract through electrostatic force, holding them together.
• For example, sodium transfers its valence electron to chlorine. Sodium becomes Na⁺, chlorine becomes Cl⁻, and their attraction forms an ionic bond.
• Magnesium oxide (MgO) and sodium fluoride (NaF) are also ionic because each pairs a metal with a nonmetal.

Covalent bonding

• In a covalent bond, atoms share electrons.
• Hydrogen atoms share electrons so each can fill its first energy level, which holds two electrons.
• Nonpolar covalent bonds share electrons equally or nearly equally. Examples include H₂, Cl₂, F₂, and C–H.
• Polar covalent bonds share electrons unequally because one atom attracts the shared electrons more strongly.
• In H–F, fluorine attracts the shared electrons more strongly than hydrogen. Fluorine becomes partially negative and hydrogen partially positive, creating a dipole.
• Electronegativity is an atom’s ability to attract electrons toward itself.

Method for classifying a bond

1. Check whether the pair contains a metal and a nonmetal. This is a useful first clue that the compound is ionic. Examples include MgO, NaF, and CaS.
2. If both atoms are nonmetals, consider a covalent bond.
   • Identical atoms share electrons equally, making Cl₂ and F₂ nonpolar covalent.
3. For different nonmetals, compare their electronegativity values.
   • Find the absolute difference between the two values.
   • The video uses a difference of 0.5 or greater to indicate a polar covalent bond.
   • A difference below 0.5 indicates a nonpolar covalent bond.
   • Examples: HBr is classified as polar covalent; IBr and C–H are classified as nonpolar covalent.
4. Use the electronegativity table supplied by the relevant textbook or course, since published values can vary slightly.

The video also notes that an O–H bond is strongly polar. It discusses hydrogen bonding in the context of hydrogen attached to oxygen, nitrogen, or fluorine. Strictly speaking, an O–H bond is polar covalent, while hydrogen bonding is a separate attraction involving such bonds.

Speakers and sources

• Speaker: An unnamed instructor or narrator from The Organic Chemistry Tutor.
• Sources and reference materials mentioned: The periodic table, electronegativity tables (including tables provided by textbooks or found through Google Images), and the physics principle that opposite charges attract.