IV.1 Compounds can be differentiated by their chemical and physical properties. (3.1dd)

IV.2 Two major categories of compounds are ionic and molecular (covalent) compounds. (5.2g)

IV.3 Chemical bonds are formed when valence electrons are (5.2a):

• transferred from one atom to another (ionic)

• shared between atoms (covalent)

• mobile within a metal (metallic)

IV.4 In a multiple covalent bond, more than one pair of electrons are shared between two atoms. (5.2e)

IV.5 Molecular polarity can be determined by the shape of the molecule and the distribution of charge. Symmetrical (nonpolar) molecules include CO2 , CH4 , and diatomic elements. Asymmetrical (polar) molecules include HCl, NH3 , and H2 O. (5.2l)

IV.6 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. (5.2c)

IV.7 When a bond is broken, energy is absorbed. When a bond is formed, energy is released. (5.2i)

IV.8 Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond. (5.2b)

IV.9 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. (5.2n)

IV.10 Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, com-pounds,

and ions. (5.2d)

IV.11 Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. Electronegativity values are assigned according to arbitrary scales. (5.2j)

IV.12 The electronegativity difference between two bonded atoms is used to assess the degree of polarity in thebond. (5.2k)

IV.13 Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetalsto form molecular (covalent) compounds. Ionic compounds containing polyatomic ions have both ionic and covalent bonding. (5.2h)