FAMILY PORTRAITGroup 1A(1): The Alkali Metals

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns1. All members have the +1 oxidation state and form an E+ion. Atoms have the largest size and lowest IE and EN in their periods. Down the group, atomic and ionic size increase, while IE and EN decrease.

Physical Properties

Metallic bonding is relatively weak because there is only one valence electron. Therefore, these metals are soft with relatively low melting and boiling points. These values decrease down the group because larger atom cores attract delocalized electrons less strongly. Large atomic size and low atomic mass result in low density; thus, density generally increases down the group because mass increases more than size.

Reactions

  1. The alkali metals reduce H in H2O from the +1 to the 0 oxidation state (E represents any element in the group):

The reaction becomes more vigorous down the group.

  1. The alkali metals reduce oxygen, but the product depends on the metal. Li forms the oxide, Li2O; Na forms the peroxide (O.N. of O = –1), Na2O2; K, Rb, and Cs form the superoxide

In emergency breathing units, KO2reacts with H2O and CO2in exhaled air to release O2(Section 22.4).

  1. The alkali metals reduce hydrogen to form ionic (saltlike) hydrides:

NaH is an industrial base and reducing agent that is used to prepare other reducing agents, such as NaBH4.

  1. The alkali metals reduce halogens to form ionic halides:

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FAMILY PORTRAITGroup 2A(2): The Alkaline Earth Metals

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2(fillednssublevel). All members have the +2 oxidation state and, except for Be, form compounds with an E2+ion. Atomic and ionic sizes increase down the group but are smaller than for the corresponding 1A(1) elements. IE and EN decrease down the group but are higher than for the corresponding 1A(1) elements.

Physical Properties

Metallic bonding involves two valence electrons. These metals are still relatively soft but are much harder than the 1A(1) metals. Melting and boiling points generally decrease and densities generally increase down the group. These values are much higher than for 1A(1) elements, and the trend is not as regular.

Reactions

  1. The metals reduce O2to form the oxides:

Ba also forms the peroxide, BaO2.

  1. The larger metals reduce water to form hydrogen gas:

Be and Mg form an oxide coating that allows only slight reaction.

  1. The metals reduce halogens to form ionic halides:
  1. Most of the elements reduce hydrogen to form ionic hydrides:
  1. The elements reduce nitrogen to form ionic nitrides:
  1. Except for amphoteric BeO, the element oxides are basic:

Ca(OH)2is a component of cement and mortar.

  1. All carbonates undergo thermal decomposition to the oxide:

This reaction is used to produce CaO (lime) in huge amounts from naturally occurring limestone.

FAMILY PORTRAITGroup 3A(13): The Boron Family

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2np1. All except Tl commonly display the +3 oxidation state. The +1 state becomes more common down the group. Atomic size is smaller and EN is higher than for 2A(2) elements; IE is lower, however, because it is easier to remove an electron from the higher energypsublevel. Atomic size, IE, and EN do not change as expected down the group because there are intervening transition and inner transition elements.

Physical Properties

Bonding changes from network covalent in B to metallic in the rest of the group. Thus, B has a much higher melting point than the others, but there is no overall trend. Boiling points decrease down the group. Densities increase down the group.

Reactions

  1. The elements react sluggishly, if at all, with water:

Al becomes covered with a layer of Al2O3that prevents further reaction.

  1. When strongly heated in pure O2, all members form oxides:

Oxide acidity decreases down the group: B2O3(weakly acidic) > Al2O3> Ga2O3> In2O3> Tl2O (strongly basic), and the +1 oxide is more basic than the +3 oxide.

  1. All members reduce halogens (X2):

The BX3compounds are volatile and covalent. Trihalides of Al, Ga, and In are (mostly) ionic solids.

FAMILY PORTRAITGroup 4A(14): The Carbon Family

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2np2. Down the group, the number of oxidation states decreases, and the lower (+2) state becomes more common. Down the group, size increases. Because transition and inner transition elements intervene, IE and EN do not decrease smoothly.

Physical Properties

Trends in properties, such as decreasing hardness and melting point, are due to changes in types of bonding within the solid: covalent network in C, Si, and Ge; metallic in Sn and Pb(see text).Down the group, density increases because of several factors, including differences in crystal packing.

Reactions

  1. The elements are oxidized by halogens:

The +2 halides are more stable for tin and lead, SnX2and PbX2.

  1. The elements are oxidized by O2:

Pb forms the +2 oxide, PbO. Oxides become more basic down the group. The reaction of CO2and H2O provides the weak acidity of natural unpolluted waters:

  1. Hydrocarbons react with O2to form CO2and H2O. The reaction for methane is adapted to yield heat or electricity:
  1. Silica is reduced to form elemental silicon:

This crude silicon is made ultrapure through zone refining for use in the manufacture of computer chips.

FAMILY PORTRAITGroup 5A(15): The Nitrogen Family

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2np3. Thenpsublevel is half-filled, with eachporbital containing one electron (parallel spin). The number of oxidation states decreases down the group, and the lower (+3) state becomes more common. Atomic properties follow generally expected trends. The large (50%) increase in size from N to P correlates with the much lower IE and EN of P.

Physical Properties

Physical properties reflect the change from individual molecules (N, P) to network covalent solid (As, Sb) to metal (Bi). Thus, melting points increase and then decrease. Large atomic size and low atomic mass result in low density. Because mass increases more than size down the group, the density of the elements as solids increases. The dramatic increase in density from P to As is due to the intervening transition elements.

Reactions

  1. Nitrogen is “fixed” industrially in the Haber process:

Further reactions convert NH3to NO, NO2, and HNO3(see text). Hydrides of some other group members are formed from reaction in water (or with H3O+) of a metal phosphide, arsenide, and so forth:

  1. Halides are formed by direct combination of the elements:
  1. Oxoacids are formed from the halides in a reaction with water that is common to many nonmetal halides:

Note that the oxidation number of E doesnotchange.

FAMILY PORTRAITGroup 6A(16): The Oxygen Family

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2np4. As in Groups 3A(13) and 5A(15), a lower (+4) oxidation state becomes more common down the group. Down the group, atomic and ionic sizes increase, and IE and EN decrease.

Physical Properties

Melting points increase through Te, which has covalent bonding, and then decrease for Po, which has metallic bonding. Densities of the elements as solids increase steadily.

Reactions

  1. Halides are formed by direct combination:
  1. The other elements in the group are oxidized by O2:

SO2is oxidized further, and the product is used in the final step of H2SO4manufacture(see text):

  1. The thiosulfate ion is formed when an alkali metal sulfite reacts with sulfur, as in the preparation of “hypo,” photographers' developing solution:

FAMILY PORTRAITGroup 7A(17): The Halogens

KEY ATOMIC PROPERTIES, PHYSICAL PROPERTIES, AND REACTIONS

Atomic Properties

Group electron configuration isns2np5; elements lack one electron to complete their outer level. The –1 oxidation state is the most common for all members. Except for F, the halogens exhibit all odd-numbered states (+7 through –1). Down the group, atomic and ionic sizes increase steadily, as IE and EN decrease.

Physical Properties

Down the group, melting and boiling points increase smoothly as a result of stronger dispersion forces between larger molecules. The densities of the elements as liquids (at the givenT) increase steadily with molar mass.

Reactions

  1. The halogens (X2) oxidize many metals and nonmetals. The reaction with hydrogen, although not used commercially for HX production (except for high-purity HCl), is characteristic of these strong oxidizing agents:
  1. The halogens undergo disproportionation in water:

In aqueous base, the reaction goes to completion to form hypohalites and, at higher temperatures, halates, for example:

FAMILY PORTRAITGroup 8A(18): The Noble Gases

KEY ATOMIC AND PHYSICAL PROPERTIES

Atomic Properties

Group electron configuration is 1s2for He andns2np6for the others. The valence shell is filled. Only Kr, Xe, and Rn are known to form compounds. The more reactive Xe exhibits all even oxidation states (+2 to +8). This group contains the smallest atoms with the highest IEs in their periods. Down the group, atomic size increases and IE decreases steadily. (EN values are given only for Kr and Xe.)

Physical Properties

Melting and boiling points of these gaseous elements are extremely low but increase down the group because of stronger dispersion forces. Note the extremely small liquid ranges. Densities (at STP) increase steadily, as expected.