Question

7 chapter morden periodic table notes
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Answer 1

The systematic arrangement of elements into groups and periods is called periodic table.

In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

So Mendeleev’s Periodic law was modified and atomic number was adopted as the basis of the Modern Periodic Table.

The Modern Periodic Law is stated as: "Properties of elements are a periodic functions of their atomic number". Atomic number is the basis for modern periodic table.

Atomic number is the number of protons in the nucleus, it is also equal to the number of electrons in the atom.

Example: In Carbon

• Elements are arranged in the increasing order of atomic numbers,Elements present in one group have the same number of valance electron.

• Horizontal rows in the periodic table are called periods and vertical columns in the table are called groups.

• Elements in the modern periodic table are arranged in 7 periods and 18 groups