(a) What are the periods and groups in a periodic table? Give two characteristics of each.
(b) In terms of electronic configurations, explain the variation in the size of the atoms of the elements belonging to the same period and same group.
(c) Given alongside is a part of the periodic table. As we move vertically downward from Li to Fr:
(i) What happens to the size of atoms? What happens to their metallic character?
(d) Name two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table. In what manner do they change?
(e) Rewrite the following statement after correction, if necessary:
Groups have elements with consecutive atomic numbers.
Li - Be
Na
K
Rb
Cs
Fr - Ra
(a) The horizontal rows of elements in a periodic table are called periods.
Characteristics:
(i) The elements in a period have consecutive atomic numbers.
(ii) The no. of elements in period is fixed by the maximum no. of electrons which can be accommodated in various shells. The vertical columns in a periodic table are called groups.
Characteristics:
(i) The elements in a group do not have consecutive atomic numbers.
(ii) All the elements in a group have similar electronic configurations and show similar properties.
(b) The size of atom decreases on moving from left to right in a period. As we move from left to right in a period, the atomic number of elements increases which means that the no. of protons and electrons in the atom increases. The electronic configuration of the atoms increases in the same shell. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of the atom decreases. On going down in a group of the periodic table, the atomic size increases. The no. of electron shells in the atoms gradually increases and the electronic configuration also increases due to which the atomic size increases.
(c)(i) The atomic size increases gradually from lithium to francium.
(ii) The metallic character increases from lithium to francium.
(d) On going down in a group of the periodic table, the atomic size and metallic character increases. When we move down from top to bottom in group 1 of alkali metals, the size of atoms increases gradually from lithium to francium. In group 1 of alkali metals, lithium is the least metallic element whereas francium is the most metallic element.
(e) Periods have elements with consecutive atomic numbers.