|Trial Elements and
|Elemental Form||Principal Compounds||Special Properties|
|(I) Cl, Br, I:
35.5, 80, 127
|Colored diatomic molecules:
|Form simple salts containing -1 ions:
Br-, I-. Form oxyanions containing one to four oxygen atoms: ClO4-, ClO3-, BrO3-, IO3-, ClO-, IO4-. Hydrogen compounds are molecular HCl, HBr, HI
|Free elements react vigorously with
electron donors to form negative ions Cl-, Br-,
2Na + Cl2 Æ 2Na+ + 2 Cl-
I2 + S2- Æ 2I- + S
Salts (like NaCl) are very soluble in water. Halide salts of Li, Na, and K give neutral solutions. Hydrogen compounds are strong acids and ionize completely in water.
HBr + H2O Æ H3O+ + Br-
|(II) S, Se, Te
32, 79, 127.6
|Colored crystalline nonmetals
(Te somewhat metallic):
|Form simple salts with -2 ions: S2-, Se2-, Te2-, and very smelly compounds with hydrogen: H2S, H2Se, H2Te. Form oxyanions with up to four oxygen atoms: SO32-,a SO42-, SeO42-. Form dioxides and trioxides SO2, SO3,a SeO2, TeO2, TeO3.||Salts, except those with triads III and IV,
are slightly soluble in water: CuS, ZnS, HgS. Soluble salts (Na2S) give basic solutions:
S2-+ H2O Æ HS- + OH-
Hydrogen compounds are weak acids.
|(III) Ca, Sr, Ba
40, 88, 137
|Reactive metals||Form salts containing +2 ions: Ca2+, Sr2+, Br2+ in BaSO4, CaCO3, SrCl2, and so on.||Salts give bright colors in flame: Ca (orange), Sr (red), Ba (green). Sulfates and carbonates are insoluble. Metals replace hydrogen slowly from water.|
|(IV) Li, Na, K
7, 23, 39
|Very reactive metals||Form salts containing +1 ions: Li+, Na+, K+ in Li2CO3, NaCl, K3PO4, and so on.||Almost all salts are soluble: metals and
salts give brightly colored flames: Li (red), Na (yellow), K (purple).
Metals react violently with water to produce hydrogen and soluble ionic
2Na + 2H2O Æ
a Note the importance of charge: SO32- is very different from SO3 (no charge).