RBSE Class 11 Chemistry Notes Chapter 3 Classification of Elements and Periodicity in Properties

These comprehensive RBSE Class 11 Chemistry Notes Chapter 3 Classification of Elements and Periodicity in Properties will give a brief overview of all the concepts.

RBSE Class 11 Chemistry Chapter 3 Notes Classification of Elements and Periodicity in Properties

→ Classification: The elements with similar properties are placed in a group this is called classification.

→ Prout’s Hypothesis: All elements are made up of hydrogen atom so all these are related to each other in their atomic weights. Since atomic weight is constant during chemical reactions. So it is considered as fundamental property of element.

→ Doberenier’s Triad: The elements in the triad had similar properties and atomic weight of middle element is very close to arithematic mean of other two elements.

→ Duma’s homologous series: Atomic weight of some elements are similar to their homologous series.

→ Newland’s Law of Octave: When elements are arranged in order of their increasing atomic weights, the properties of each eighth elements is similar to first one.

→ Lothar Meyer’s Curve: Lothar Meyer plotted a curve between physical properties of elements and atomic weight and found that elements having similar properties occupied similar positions.

→ Mendeleev’s Periodic Law: “The physical and chemical properties of elements are periodic function of their atomic weights.”

→ Periodictiy: Repetition of physical and chemical properties after a regular interval is known as periodicity

→ Periods: These are horizontal lines in periodic table.

→ Groups: These are vertical columns in periodic table.

→ Representative or Typical Elements: The elements of second period from Li to F and elements of third period from Na to Cl are known as typical elements

→ Transition Elements: Such elements of group 3rd to 12th which are different from representative elements in behaviour.

→ Modern Periodic Law: The physical and chemical properties of elements are periodic function of their atomic number.

→ Atomic Radius: The distance between nucleus and outer most shell of electrons is called atomic radius.

→ Covalent Radius: It is one half of the distance between the centres of nucleus of two similar atoms bonded by single covalent bond.

→ vander Waals radius: It is one half of the inter- nuclear distance between two adjacent atoms belonging to two nearest neighbouring molecules of the substance in the solid state.

→ Metallic Radius: One half of internuclear distance between the two neighbouring atoms in a metal lattice is called metallic radius.

→ Effective Nuclear Charge: The net charge of nucleus by outermost electron known as effective nuclear charge
Effective nuclear charge = Nuclear charge - Screening effect

→ Ionic Radius: The distance between nucleus and outermost electrons in an ion is called ionic radius.

→ Ionization Enthalpy: The amount of energy required to remove the most loosely bounded electron from an isolated gaseous atom is called ionization energy or ionization enthalpy.

→ Electron Affinity: The amount of energy released when an electron is added to an isolated gaseous atom is called electron affinity or electron gain enthalpy.

→ Electronegativity: It is the tendency of an element to attract shared pair of electrons toward itself and is called electronegativity.

→ Valency: Valency is defined as the number of hydrogen or halogens atoms combined to atom of an element or number of double of oxygen atom combined.

→ Some Important Facts:

• Periodic classification of elements was explained by many scientists. Some are given as follows:
  (a) Dobereiner triad
  (b) Newlands law of octave
  (c) Lothar Meyer’s curve
  (d) Mendeleev’s periodic law
• In periodic table vertical columus are known as groups. They are 18 in numbers.
• The horizontal lines in periodic table are known as periods and there are 7 periods in periodic table.
• Elements of d-block are known as transition elements, whereas /-block elements are known as inner transition elements.
• Following are the general electronic configurations:
  • s-block elements - ns^1-2
  • p-block elements - ns²np^1-6
  • d- block elements -(n - 1)^d1-10ns1-2
  • f-block elements (n - 2)f^1-14 (n - 1 )d^0-1ns²
• Ionic and atomic radii increase on moving down the group.
• Moving on left to right in a period, ionization enthalpy and electron gain enthalpy increases whereas on moving down in group decreases.