# AP Inter 1st Year Chemistry Notes Chapter 2 Classification of Elements and Periodicity in Properties

Students can go through AP Inter 1st Year Chemistry Notes 2nd Lesson Classification of Elements and Periodicity in Properties will help students in revising the entire concepts quickly.

## AP Inter 1st Year Chemistry Notes 2nd Lesson Classification of Elements and Periodicity in Properties

→ Mendeleeff’s periodic law :
“The properties of the elements and their compounds are a function of their atomic weights”.

→ EKa Al – Gallium,
EKa Si – Germanium,
EKa B – Scandium.

→ Ar – k, CO – Ni, Te – l, Th – Pa are called anomalous pairs.

→ $$\sqrt{\vartheta}$$ = a(Z – b) is Moseley’s equation. ‘Moseley’ concluded that an element is characterized by its atomic number and not by atomic mass.

→ Modern periodic law : “The physical and chemical properties of the elements are periodic functions of their atomic numbers”.

→ Moseley’s Periodic law : The physical and chemical properties of all elements are periodic function of their atomic number.

→ The physical and chemical properties of all elements are periodic function of their electronic configuration, is Bohr’s periodic law.

→ Long form of the periodic table has 7 periods and 18 groups (16 groups because VIII group consists three vertical columns).
II period elements are called bridge elements.
III period elements are called typical element.
‘s’ block and ‘p’ block elements except zero group elements are known as representative elements; rd’ block elements are called transition elements, f block elements are known as inner transition elements.

→ Ionization potential is the amount of energy required to remove the most loosely held elec¬tron from a neutral gaseous atom.

→ The element with highest ionization potential is ‘He’ and with least ionization potential is ‘Cs’

→ Three types of atomic radii are
a) Crystal (or) atomic radius
b) Vander Waals radius
c) Covalent radius

→ The decrease in size of the atoms or ions- among the lanthanides is known as lanthanide contraction.

→ Electronegativity can be defined as the ability of an atom to attract the shared electron pair in a molecule towards itself.

→ The element with the highest electronegativity is Fluorine (4.0).

→ Electronegativity can be calculated by Mulliken scale, Pauling scale and Allred – Rochow scale.

→ Electron affinity can be defined as the amount of energy released when an electron is added to a neutral gaseous atom in its ground state.
The element with the highest electron infinity is°thlorirl^^l 1%.

→ Inert pair effect: The reluctance of the outermost ‘s’ electron pair to take part in a chemical reaction is called inert pair effect. It increases down a group.

→ Diagonal relationship ; On moving diagonally across the periodic table the elements show certain similarities. The first element of the group resembles to some extent the second ele-ment of the next higher group. This type of resemblance is called diagonal relationship.
e.g. : (Li, Mg); (Be, Al); (B, Si)

→ Polarizing power = $$\frac{\text { ionic charge }}{\text { (ionic radius) }^2}$$
Diagonally related elements possess the same polarizing power.

→ The sizes of actinide elements decrease regularly along the series because the extra charge on the nucleus is poorly shielded by the f – electrons. This results in “Actinide contraction”.