CBSE Class 11-science Chemistry Classification of Elements and Periodicity in Properties
Modern Periodic Law
Dobereiner's Triads were arranged according to similar chemical and physical properties
Mendeleev's Periodic Law: If all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained.
Modern periodic table is the arrangement of elements in increasing order of atomic number.
The physical and chemical properties of the elements are periodic functions of their atomic numbers.Nomenclature of Elements
Atomic number is not only responsible for the IUPAC name it also indicates how many electrons are there in an atom.
Electronic configuration is denoted by shells or level and subshell or,orbitals and the number of electrons in respective orbitals.
Filling is done as per n + l rule where n is the principal and l is the azimuthal quantum number4 Blocks in Periodic Table
The extreme left of the periodic table is s-block, right is the p-block, sandwiched in between is d block and at the bottom is the f-block.
s-Block has 2 groups as s orbital has only 2 electrons.
p-Block constitutes groups 13-18Trends in Properties of Elements
Atomic radius, electro negativity decreases down the group and increases along the period.
Electron gain enthalpy become more negative across a period and less negative down the group.
Most of the properties of the elements such as atomic volume, atomic size, ionisation enthalpy, electron gain enthalpy and electronegativity are directly related to the electronic configuration of the atoms.Trends in Chemical Properties
There is some periodicity in valence for example among representative elements; the valence is either equal to the number of electrons in the outermost orbitals or eight minus this number.
Chemical reactivity is highest at the two extremes of a period and is lowest in the centre.
Anomalous behaviour of the first member of second period is due to their small size, large charge/radius ratio and high electronegativity of the elements.
