CBSE Class 11-science Chemistry Classification of Elements and Periodicity in Properties
Modern Periodic Law
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
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 number
4 Blocks in Periodic Table
s-Block has 2 groups as s orbital has only 2 electrons.
p-Block constitutes groups 13-18
Trends in Properties of Elements
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
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.
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