The elements in which the last electron enters the outermost s-orbital are called s-block elements. The group 1 and 2 of periodic table belong to the s-block.
The elements of Group-1 of Periodic Table are Li, Na, K, Rb, Cs Fr (Radioactive: t1/2 of Fr233 = 21 minutes). Group-1 elements are called alkali metals because they form hydroxides on reaction with water, which are alkaline in nature.
Electronic configuration
The alkali elements in the s-block consist of a single valence electron in their outermost shell. This outermost electron is loosely held which makes these metals highly electropositive. Due to which they are not available in the free state in nature. The general electronic configurations of s block elements – group 1 are as shown in the table below:
Trend Down Group 1 of Alkali Metals
Rubidium is used in: a compound of rubidium is used to treat depression.
Cesium is used in: glass and radiation detection equipment.
Francium is not used in anything except for research because it is one of the rarest elements and it is a radioactive element.
The Group 1 elements, also known as the alkali metals, include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). These elements are highly reactive and form compounds with a wide range of other elements. Discussed below are some important compounds of Alkali Metals or Group-1 Elements.
Controlled oxidation of alkali metals like sodium and potassium with moisture-free oxygen gas at around 300°C gives peroxides.
2M + O2 → M2O2
Peroxides form hydrogen peroxide with cold water and oxygen at higher temperatures.
M2O2 + 2H2O → H2O2 + 2MOH
2M2O2 + 2H2O → O2 + 4MOH
Alkali metal peroxides are used to produce other peroxides, bleach, preparing perborate and purification of air in small spaces.
It is prepared by heating potassium with excess oxygen or passing ozone through potassium Hydroxide. It is an orange solid and paramagnetic. Superoxides of alkali metals are a powerful oxidizing agent due to the release of hydrogen peroxide and oxygen in an aqueous solution.
2KO2 + 2H2O → H2O2 + O2 + 2KOH
It is prepared by the Solvay process. Raw materials needed are brine, carbon dioxide and ammonia. Carbon dioxide is obtained by calcining limestone. Ammonia and carbon dioxide react to form ammonium bicarbonate, which is used to precipitate less soluble sodium bicarbonate from the aqueous solution using brine.
On heating, bicarbonate produces sodium carbonate. Calcium oxide on treatment with water gives calcium hydroxide which on treating with the byproduct releases ammonia for reuse.
CaCO3 + 2NaCl → Na2CO3 + CaCl2
Sodium bicarbonate is precipitated out of a concentrated aqueous solution of sodium carbonate by carbon dioxide.
Na2CO3 + H2O + CO2 → 2NaHCO3
The aqueous solution is alkaline. The bicarbonate ion is amphiprotic i.e. both proton donor and acceptor.
Baking soda is a mixture of sodium bicarbonate and weak solid organic acids like tartaric acid and a diluent like cornstarch. The mixture produces carbon dioxide by the reaction between the acid and the carbonate giving a porous structure in baking products.
Hydroxides are produced by the electrolysis of an aqueous solution of brine. Hydrogen and chlorine are obtained as the by-products. Hydroxides of alkali metals are strong bases. They are deliquescent and form carbonate by reacting with carbon dioxide. Some metal salts of Zn, Al, precipitate metallic hydroxides, which dissolve in excess alkali.
ZnCl2 + 2NaOH → Zn(OH)2 + 2NaCl
Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O
1. What are S-Block Elements?
Ans. S-Block elements are the elements in the periodic table that belong to the first two groups, i.e., Group 1 and Group 2. These elements have valence electrons in the S orbital, and their properties are mainly characterized by the presence of one or two valence electrons.
2. What are the physical properties of Group-1 Elements?
Ans. Group-1 elements, also known as alkali metals, have some common physical properties, such as low densities, low melting and boiling points, and high reactivity. They have a silvery-white appearance and are soft and malleable.
3. What are the chemical properties of Group-1 Elements?
Ans. The alkali metals are highly reactive due to their low ionization energies and the presence of only one valence electron. They readily react with non-metals such as halogens, oxygen, and water, forming ionic compounds. They also have a strong tendency to lose their valence electron and form cations.
4. What are the uses of Group-1 Elements or Alkali Metals?
Ans. The alkali metals have several important uses in different industries. For example, sodium and potassium are used in the production of soaps and detergents, while lithium is used in batteries. Sodium is also used in the production of chemicals and in the purification of metals, and potassium is used in fertilizers.
5. What are the different compounds of Group-1 Elements?
Ans. Group-1 elements form different compounds, such as oxides, hydroxides, and halides. For example, sodium forms sodium oxide, Na2O, and sodium hydroxide, NaOH. Similarly, potassium forms potassium oxide, K2O, and potassium hydroxide, KOH. The halides of these elements, such as sodium chloride (NaCl) and potassium iodide (KI), are also widely used.
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1. What are S-Block Elements? |
2. What is the electronic configuration of Group-1 elements? |
3. What are the physical properties of Group-1 elements? |
4. What are the chemical properties of Group-1 elements? |
5. What are the uses of Group-1 elements or alkali metals? |
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