NEET Study Notes for S- block elements: S block elements consist of Group 1 and Group 2 elements. These consist of elements with either 1 or electrons in the s-subshell. The elements with 1 electrons are called Group 1 elements or alkali metals while elements with 2 electrons are called Group 2 elements or alkaline earth metals.
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Topics | Sub-Topics |
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S-block elements | Group I and group 2 elements: General introduction, electronic configuration, occurrence, anomalous properties of the first element of each group, diagonal relationship, trends in the variation of properties (such as ionization enthalpy, atomic and ionic radii), trends in chemical reactivity with oxygen, water, hydrogen and halogens; uses. Preparation and Properties of Some important Compounds: Sodium carbonate, sodium chloride, sodium hydroxide and sodium hydrogencarbonate, biological importance of sodium and potassium. |
Due to the looselh held electrons, alkali metals have high electropositivity. This is why they arenot available in free state. The general electronic configuration for Group 1 S block elements are tabulated bellow;
Elements | Electronic Configuration |
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Li | [He] 2 s1 |
Na | [Ne] 3 s1 |
K | [Ar] 4 s1 |
Rb | [Kr] 5 s1 |
Cs | [Xe] 6 s1 |
Fr | [Rn] 7 s1 |
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The relationship between adjacent elements that are present in the second and third periiod is termed as the diagonal relationship between S block elements. Here the properties of elements that are diaogonally located, show similar characteristics.
For example- berrilyium (located in 2nd group and 2nd period ) have similar properties to allumnium ( located in 3rd group and 3rd period). Diagonal relationship between S block elements is witnessed from left to right and down the group.
For Example- Berrylium and and Allumnium
Berrylium and Allumnium Ions are when beryllium hydroxide and allumnium hydroxide reacts with alkali in excess. The presence of oxide, prevents these elements to get affected acid attack. Berrylium and Allumnium tend to form complex compounds. In organic solvents, chlorides of the elements are soluble.
Due to the large atomic size and consequent decrease of I.E. alkali metals alkali metals except Lithium form Ionix xompounds. Lithium can form covalent as well as ionic compounds. Alkali metlas are highly reactive.
Alkali Metals react with water and forms Hydrogen
Examples of this reaction are
where M is any alkali metal
Reactivity with water increases down the group from Li to Cs in the following order. This is due to increase in electropositive nature
Li<Na<K<Rb<Cs
Ionic Hydrides are form on reaction of alkali metals with Hydrogen. Down the group, reactivity with hydrogen decreases. This order is
Li>Na>K>Rb>Cs
Stability of these Hydrides in increasing order is LiH>NaH>KH>RbH>CsH
On heating alkali metals with Oxygen, oxides like lithium oxide, sodium oxide and sodium peroxide are formed. Lattice energy helps in stabilisation of larger anions through the larger cations. Stability of these oxides and peroxides formed increases from Li to Cs due to this.
Oxides, Peroxides and Superoxides have basic nature. Solubility and increase in oxide strength in increasing order is
Stability of peroxides and superoxided in the increasing order is
Ionic Halides are formed on reaction of alkali metals with Hydrogen. Reactivity with Halogens in increasing order is
These alkali halides are soluble in water.
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These are less reactive in relation to alkali metals as the Ionization enthalpy is low. The reaction increases down the group due to decreasing ionization enthalpy
Hydrogen gas is formed on reaction of alkaline metals with water. On moving from Mg to Ba reaction of alkaline metals with water inctreases. However Ba reacts vigorously even with cold eater . In the increasing order of reactivity with water is
Mg<Ca<Sr<Ba
Hydides are formed on reaction of alkaline metals with hydrogen through the process of heating. Only Be does not react with Hyrogen These hyides also react with water to form Hydrogen gas. These also behave as strong reducinga agents.
Example-
Halides are formed un when these elements react with halogen at high temperature. The hallides have solubility in water. As the atomic size increases, their ionic character also increases.
Reactivity with Oxygen increases as we move down the group. Be, Mg and Ca formsmonoxides on heating with oxygen while peroxides from Sr, Ba and Ra.
Example-
Sodium Carbonate is a white powder and odourless diaozium salt of carbonic acid. It dissolves in water to form to form carbonic acid and sodium hydroxide. Sodium carbonate is also known as washing soda, soda crystals. Washing soda or soda crystals.
The four main ways of preparation of Sodium Carbonate is Solvay, Labnac, Dual and electrolytic process.
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The ionic compound in which the proportion os sodium and ions is in equal ratio is called Sodim Chloride. Chemical formula of Sodium Chloride is NaCl, Sodium Chloride has wide applications in household as well as industries. The common name of sodium chloride is table salt,common salt and halite.
Sodium oxide is a simple inorganic compound that is in the form of a solid state in white color at room temperature. Ph of a substance can be determined by using sodium hydroxide with neutral water and acid. The chemical formular of Sodium Hydroxide is NaOH. It is also known as caustic soda and manufacturing products like paper, soap, detergents, explosives and cleaners etc.
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Sodium Bicarbonate, also known as Sodium hydrogen carbonate is a white powder like substance. It is formed from sodium and bicarbonate ions. This is also known as baking soda. The chemical formula of Sodium bicarbonate is NaHCO3.
Question: Element of atomic number 56 belongs to which of the following group
Answer: s- block
Question: Why are the properties of Lithium and Magnesium similar?
Answer: Due to diagonal relationship
Question: Potassium is an element from which of the following groups?
Answer: Alkali Metals
Question: In comparison to K, Na has a
Answer: higher ionization energy
Question: With which element is the diagonal relationship of Be seen?
Answer: Al
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