Summary
Highlights
A bond between two atoms of the same element, like two hydrogen atoms (H-H), is a nonpolar covalent bond because the electrons are shared equally due to identical electronegativity, resulting in an equal pull on electrons.
When two nonmetals bond, like carbon and oxygen, it's typically a covalent bond. To determine if it's polar, compare their electronegativity values. Carbon has an electronegativity of 2.5 and oxygen has 3.5. A difference of 1.0 (greater than 0.5) indicates a polar covalent bond, where electrons are shared unequally. Oxygen, being more electronegative, gains a partial negative charge, and carbon a partial positive charge. Bond polarity is indicated by an arrow pointing towards the more electronegative element.
Bonds between a metal and a nonmetal, such as sodium and chlorine, are typically ionic bonds. In ionic bonds, electrons are transferred rather than shared. Sodium (metal) transfers its electron to chlorine (nonmetal), resulting in sodium becoming a positively charged cation and chlorine a negatively charged anion. The electrostatic attraction between these opposite charges forms the ionic bond.
The bond between carbon (electronegativity 2.5) and hydrogen (electronegativity 2.1) has an electronegativity difference of 0.4. This classifies it as a nonpolar covalent bond. Molecules composed only of carbon and hydrogen, like methane or hexane, are nonpolar molecules and do not dissolve in polar substances like water.
A bond between two carbon atoms is always a nonpolar covalent bond because both atoms have the same electronegativity, leading to a zero difference and equal sharing of electrons.
The bond between oxygen (electronegativity 3.5) and hydrogen (electronegativity 2.1) has a difference of 1.4, making it a highly polar covalent bond. This is a special type of polar bond known as a hydrogen bond, formed when hydrogen is directly attached to nitrogen, oxygen, or fluorine. Hydrogen bonds are powerful intermolecular forces, responsible for water's high boiling point. Oxygen assumes a partial negative charge, and hydrogen a partial positive charge.
The bond between lithium (a metal) and fluorine (a nonmetal) is an ionic bond. Immediately identifying the elements as a metal and a nonmetal signals an ionic interaction, characterized by a significant electronegativity difference and electron transfer, with lithium becoming a cation and fluorine an anion.