CBSE Class 11 Chemistry Classification Of Elements And Periodicity In Properties Of Elements Notes Set C

CBSE Class 9 Chemistry-Classification Of Elements And Periodicity In Properties Of Elements. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

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CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES OF ELEMENTS

IMPORTANT POINTS

ATOMIC RADIUS- The distance from the center of the nucleus to the outermost shell of the electrons in the atom of any element is called its atomic radius.

• Decreases from left to right in a period.

• Increases on moving top to bottom in a group.

COVALENT RADIUS- Half the inter-nuclear distance between two similar atoms of any element which are covalently bonded to each other by a single covalent bond is called covalent radius.

VANDER WAAL’S RADIUS: Half the inter-nuclear separation between two similar adjacent atoms belonging to the two neighboring molecules of the same substance in the solid state is called the van der Waals’ radius of that atom.

METALLIC RADIUS: Half the distance between the nuclei of the two adjacent metal atoms in a close packed lattice of the metal is called its metallic radius. Van der Waals ’radius > Metallic radius > Covalent radius

IONISATION ENTHALPY: The ionization enthalpy is the molar enthalpy change accompanying the removal of an electron from a gaseous phase atom or ion in its ground state. Thus enthalpy change for the reaction.M (g)→ M++ e-Generally the ionisation enthalpies follow the order ( there are few exceptions): (ΔiH1) < (Δ_iH₂)< (Δ_iH₃)

Periodicity in IONISATION ENTHALPY:

i) The ionisation enthalpy decreases on moving top to bottom in a group. 

ii) The ionisation enthalpy increases on moving from left to right in a period

ELECTRON GAIN ENTHALPY: The electron gain enthalpy ((ΔegH) is the molar enthalpy change when an isolated gaseous atom or ion in its ground state adds an electron to form the corresponding anion thus the enthalpy change for the reaction;X(g)+ e- → X

Periodicity in ELECTRON GAIN ENTHALPY:

(i) In period- The electron gain enthalpy increases from left to right in a period.

(ii) In group- The electron gain enthalpy decreases from top to bottom in a group.

ELECTRONEGATIVITY: “The relative tendency of an atom in a molecule to attract the shared pair of electrons towards itself is termed as its electro- negativity.”

Periodicity in ELECTRONEGATIVITY:

(i) In period- The electro-negativity increases from left to right in a period.

(ii) In group- The electro-negativity decreases from top to bottom in a group.

ELECTRO-NEGATIVE OR NON- METALLIC CHARACTERS: the tendency of an element to accept electrons to form an anion is called its non-metallic or electronegative character. The elements having high electro-negativity have higher tendency to gain electrons and forms anion. So, the elements in the

upper right hand portion of the periodic table are electro-negative or non-metallic in nature.

SOLUBILITY OF ALKALI METALS CARBONATES AND BICARBONATES:

PERIODICITY IN GROUP: The solubility of alkali metal carbonates and bicarbonates in water increases down the group (From Lithium to Caesium).

SOLUBILITY OF ALKALINE EARTH METAL HYDROXIDES AND SULPHATES:

PERIODICITY IN GROUP: The solubility of alkaline earth metal hydroxide and sulphates in water increases down the group (From Beryllium to Barium).

BASIC STRENGTH OF ALKALINE EARTH METAL HYDROXIDES:

PERIODICITY IN GROUP: The basic strength of alkaline earth metal hydroxide in water increases down the group (From Beryllium to Barium), i.e., Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂ <Ba(OH)₂ Basic strength increases

THERMAL STABILITY OF CARBONATES OF ALKALI AND ALKALINE EARTH METALS:

Except lithium carbonate, (Li₂CO₃), the carbonates of all other alkali metals are stable towards heat, i.e., carbonates of alkali metals (except Li₂CO₃) do not decompose on heating. Li₂CO₃ decomposes on heating to give lithium oxide (Li₂CO₃).

The carbonates of alkaline earth metals are relatively less stable. On heating, they decomposeto give corresponding oxide and CO₂ gas. The decomposition temperature for alkaline earth metal carbonates increases as we go down the group.

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