Chapter 7 Periodic Properties of the Elements

Nonmetals Dull, brittle substances that are poor conductors of heat and electricity. Tend to gain electrons in reactions with metals to acquire noble gas configuration. Periodic Properties

of the Elements Nonmetals Substances containing only nonmetals are molecular compounds. Most nonmetal oxides are acidic. Periodic Properties

of the Elements Metalloids Have some characteristics of metals, some of nonmetals. For instance, silicon looks shiny, but is brittle and fairly poor conductor. Periodic

Properties of the Elements Group Trends Periodic Properties of the Elements Alkali Metals Soft, metallic solids.

Name comes from Arabic word for ashes. Periodic Properties of the Elements Alkali Metals Found only as compounds in nature. Have low densities and melting points. Also have low ionization energies.

Periodic Properties of the Elements Alkali Metals Their reactions with water are famously exothermic. Periodic Properties of the Elements

Alkali Metals Alkali metals (except Li) react with oxygen to form peroxides. K, Rb, and Cs also form superoxides: K + O2 KO2 Produce bright colors when placed in flame. Periodic Properties of the Elements

Alkaline Earth Metals Have higher densities and melting points than alkali metals. Have low ionization energies, but not as low as alkali metals. Periodic Properties of the Elements Alkaline Earth Metals Be does not react

with water, Mg reacts only with steam, but others react readily with water. Reactivity tends to increase as go down group. Periodic Properties of the Elements

Group 6A Oxygen, sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioactive polonium is a metal. Periodic Properties of the Elements Oxygen Two allotropes:

O2 O3, ozone Three anions: O2, oxide O22, peroxide O21, superoxide Tends to take electrons from other elements Periodic (oxidation)

Properties of the Elements Sulfur Weaker oxidizing agent than oxygen. Most stable allotrope is S8, a ringed molecule. Periodic Properties

of the Elements Group VIIA: Halogens Prototypical nonmetals Name comes from the Greek halos and gennao: salt formers Periodic Properties of the Elements

Group VIIA: Halogens Large, negative electron affinities Therefore, tend to oxidize other elements easily React directly with metals to form metal halides Chlorine added to water supplies to serve as disinfectant Periodic

Properties of the Elements Group VIIIA: Noble Gases Astronomical ionization energies Positive electron affinities Therefore, relatively unreactive Monatomic gases Periodic

Properties of the Elements Group VIIIA: Noble Gases Xe forms three compounds: XeF2 XeF4 (at right) XeF6 Kr forms only one stable compound:

KrF2 The unstable HArF was synthesized in 2000. Periodic Properties of the Elements