Group 1 Elements: Alkali Metals
Table of Content
- Periodic Table of Elements
- Physical properties of Alkali Metals
- Chemical properties of Alkali Metals
- Uses of Alkali Metals
Group 1 elements are known as Alkali Metals. It includes Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). This group lies in the s block of the periodic table. They are known as s Block Elements as their last electron lies in the s-orbital.
They are shiny, highly reactive metals. They are generally kept in certain solutions such as oil to prevent reactivity with the air. They are so soft that they can be easily cut via knife. Out of all the alkali metals, sodium is the most abundant metal. Francium is rarely found as it is radioactive in nature.
The Periodic Table is a tabular arrangement of the chemical elements, ordered by their atomic number (number of protons), electronic configurations, and recurring chemical properties. This ordering shows periodic trends, such as elements with similar behavior in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right.
- They possess metallic bonding.
- They are soft with low densities, melting point and boiling point.
- Generally, they are crystalline in nature.
- They produce different colors with flame test. Flame test is an analytical test used to detect the presence of certain metals based on their emission spectrum.
- The electronic configuration of all alkali metals is given below:
Fig.1. Electronic configuration of alkali metals
- When moving from top to bottom in a group atomic radius increases.
- Electronegativity decreases from lithium to francium. So, lithium has highest electronegativity.
- They possess lower first ionization energies as they are highly reactive.
- They have lower effective nuclear charge when one moves left to right in a column.
- They can attain noble gas configuration after losing their valence electron.
- The melting and boiling points follow the trend: fluoride > chloride > bromide > iodide, that is, fluorine has highest boiling point due to its small size. As size increases boiling point decreases.
Reactivity of alkali metals increases down the group:
- Reactivity towards air- As they are highly reactive, they form an oxide layer when exposed to the dry atmosphere. When they are exposed to moisture, they form hydroxides. Lithium forms monoxide, sodium forms peroxide, and others forms peroxide. The oxides and peroxide form is colorless but superoxides are colorful.
4 Li +O →2Li O (oxide)
K + O2 → KO2
- Reactivity towards water- Alkali metals forms hydroxide and dihydrogen on reaction with water. Hydroxides are white, crystalline solids.
- Reactivity towards di-hydrogens- The alkali metals react with dihydrogen at about 673K to form hydrides. All the alkali metal hydrides are ionic solids with high melting points.
- Reactivity towards halogens- Alkali metals react vigorously with halogens to form ionic halides. This is due to lower first ionization energies. Lithium halides are covalent in nature. This is due to high polarization capability of lithium ion.
2Na(s) + Cl2(g) → 2NaCl(s)
- Reducing nature of alkali metals- They are very strong reducing agents. Lithium is the strongest reducing agents whereas sodium is the weakest reducing agents. Lithium being small in size has the highest hydration enthalpy.
- Solutions in liquid ammonia- All alkali metals dissolve in liquid ammonia to give deep blue solutions. This reaction produces ions which are conducting in nature. The blue colour of the solution is due to the formation of ammoniated electron which absorbs energy in the visible region of light. This imparts blue color to the solution. The solutions are paramagnetic (free electrons).
M+(x + y) NH3 → [M(NH3 )x ]+ +[e(NH3 )y ]−
- Reaction with oxo-acids- All alkali metals forms salts with oxo-acids. Oxoacid is a compound with hydrogen, oxygen, and atleast one other element that can dissociate to produce hydrogen ion.
Fig. 4. Oxo-acids
- Lithium is used in preparing alloys.
- Lithium is also used in thermonuclear reactions. It is also used in electrochemical cells.
- Liquid sodium is used as a coolant in nuclear reactors.
- Potassium is used in biological systems such as, opening and closing of stomata.
- Potassium hydroxide is used as an absorbent of carbon-dioxide.
- Potassium chloride is used as fertilizer in agriculture.
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