The Modern Periodic
Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’.
Mendeléev arranged
the elements in increasing order of their atomic masses and according to their
chemical properties.
The term atomic
size refers to the radius of an atom. The atomic size may be visualised as the
distance between the centre of the nucleus and the outermost shell of an
isolated atom.
Atomic radius decreases
in moving from left to right along a period. This is due to an increase in
nuclear charge which tends to pull the electrons closer to the nucleus and
reduces the size of the atom.
Atomic size increases
down the group. This is because new shells are being added as we go down the
group. This increases the distance between the outermost electrons and the nucleus
so that the atomic size increases in spite of the increase in nuclear charge.
Metalloids or
semi-metals.- these exhibits some properties of both metals and non-metals.
Next Topic:-Science Class 10 NCERT Textbook- Lesson-6
