5.2a Chemical bonds are formed when valence electrons are:

• transferred from one atom to another (ionic)

• shared between atoms (covalent)

• mobile within a metal (metallic)

5.2b Atoms attain a stable valence electron configuration by bonding with other atoms.

Noble gases have stable valence configurations and tend not to bond.

5.2c When an atom gains one or more electrons, it becomes a negative ion and its

radius increases. When an atom loses one or more electrons, it becomes a positive ion

and its radius decreases.

5.2d Electron-dot diagrams (Lewis structures) can represent the valence electron

arrangement in elements, compounds, and ions.

5.2e In a multiple covalent bond, more than one pair of electrons are shared between

two atoms. Unsaturated organic compounds contain at least one double or triple bond.

5.2f Some elements exist in two or more forms in the same phase. These forms differ in

their molecular or crystal structure, and hence in their properties.

5.2g Two major categories of compounds are ionic and molecular (covalent)


5.2h Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to

react with other nonmetals to form molecular (covalent) compounds. Ionic compounds

containing polyatomic ions have both ionic and covalent bonding.

5.2i When a bond is broken, energy is absorbed. When a bond is formed, energy is


5.2j Electronegativity indicates how strongly an atom of an element attracts electrons

in a chemical bond. Electronegativity values are assigned according to arbitrary scales.

5.2k The electronegativity difference between two bonded atoms is used to assess the

degree of polarity in the bond.

5.2l Molecular polarity can be determined by the shape of the molecule and distribution

of charge. Symmetrical (nonpolar) molecules include CO2 , CH4 , and diatomic elements.

Asymmetrical (polar) molecules include HCl, NH3 , and H2 O.

5.2m Intermolecular forces created by the unequal distribution of charge result in varying

degrees of attraction between molecules. Hydrogen bonding is an example of a

strong intermolecular force.

5.2n Physical properties of substances can be explained in terms of chemical bonds and

intermolecular forces. These properties include conductivity, malleability, solubility,

hardness, melting point, and boiling point.