Characteristics of Chemical Bonds Chapter 12 Section 12.1 & 12.2

Chemical Bonds So what is a chemical bond? ANS: A force that holds two or more atoms together and makes them function as a single unit. Are all chemical bonds the same? ANS: NO! The some chemical bonds require more energy than others to break. This is called “bond energy.”

Chemical Bonds There are two (2) types of chemical bonds: Ionic Bonds – the electromagnetic attraction between two (2) oppositely charged ions.

Ionic Bonds ALWAYS a METAL plus a NONMETAL. The metal always loses e‾‘s to form cations (+). The nonmetal always gains e‾‘s to form anions ( ̶ ).

Properties of Ionic Compounds Also known as “salts” Solids at room temperature Crystalline lattice structure High melting points and boiling points Ions totally dissociate when dissolved in water. Conduct electricity when dissolved in water, but not as solids

Chemical Bonds Covalent Bonds – a force that holds two atoms together by the sharing of one or more pair(s) of electrons.

Chemical Bonds Not all electron pairs are shared equally. Different atoms have different attractions for electrons. This is called electronegativity – the relative ability of an atom in a molecule to attract a pair of electrons to itself.

Electronegativity Generally, electronegativity INCREASES from LEFT to RIGHT, and DECREASES from TOP to BOTTOM on the Periodic Table. DECREASES INCREASES

As the difference in electronegativities increases, the polarity of the bond increases.

Covalent Bonds Electrons are ALWAYS SHARED in covalent bonds! ALWAYS a NONMETAL and a NONMETAL Electrons are ALWAYS SHARED in covalent bonds!

Properties of Molecular Compounds Solids, liquids, or gases at room temperature Low melting points and boiling points Molecules remain intact if dissolved in water Does NOT conduct electricity in pure form or dissolved in water