Question

list six chemical or physical properties typical of alkali metal elements

Answer 1

physical properties The densities of alkali metals are much lower when compared to other metals.
Unlike other metals, the elements of the alkali metal group are soft substances and can be cut with a knife.
In any given period of the periodic table, the atomic radii of the alkali metals is largest, and the atomic radius increases as one moves down the group.
The members of this group have low ionization energies, which is the energy required to remove the outermost electron from the orbit. The ionisation energy decreases as one moves down the group.
They are good conductors of heat and electricity.
They have very low boiling and melting points.
Except for cesium, which has a light golden color, alkali metals are silvery white in color.
They are lustrous and have a shiny surface.
They are highly malleable and ductile, which means they can be easily drawn into thin wires and beaten into thin sheets.
They form colored flames when burning in oxygen.
Two of the group's members, potassium and rubidium exhibit weak radioactive properties.

Answer 2

chemical properties
1. Reaction with Oxygen

Any alkali metal, on coming in contact with air or oxygen, starts burning and oxides are formed in the process. At the end of the chemical reaction, lithium gives lithium monoxide(LiO), sodium gives sodium peroxide (Na2O2) and other alkali metals give superoxides (that is, each alkali metal atom forms bonds with two oxygen atoms). Oxides of alkali metals are basic in nature and are soluble in water, forming alkali metal hydroxides on dissolving in water.

The table below enlists the color of the flame emitted when the alkali metals burn in oxygen.

Alkali Metal Flame Color
Lithium (Li) Crimson
Sodium (Na) Intense Yellow
Potassium (K) Lilac
Rubidium (Rb) Red-violet
Cesium (Cs) Blue-violet

Actually, alkali metals have a shiny surface but they get tarnished very easily, as a result of oxidation with the atmospheric oxygen and their appearance becomes dull.

2. Reaction with Hydrogen

When alkali metals react with hydrogen, then ionic hydrides are formed. The ionic nature of the hydrides increases as we move down from lithium to cesium. The stability of the hydrides thus formed, reduces with the increase in the atomic numbers of alkali metals. These hydrides have strong reducing properties.

3. Reaction with Halogens

Alkali metals react with elements of the halogen group (Group 17 of the periodic table), to form halides. Except lithium iodide, all other halides are ionic in nature. To some extent, lithium iodide is covalent in nature as the bonding occurs between the smallest cation and the largest anion. As a result, the large iodide anion gets polarized. All the halides, except lithium fluoride (LiF), readily dissolve in water.

4. Reaction with Water

Alkali metals react with water to form hydroxides and hydrogen gas is released in the process. The reaction is so vigorous in nature that the hydrogen gas produced during the reaction catches fire. Lithium is the only alkali metal that reacts slowly with water. The hydroxides possess strong basic properties. The strength of the basic properties of alkali metal hydroxides increase with rise in atomic number of the alkali metals.