(a) What is meant by periodicity in properties of elements with reference to the periodic table ?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period ? Explain
(a) What is meant by periodicity in properties of elements with reference to the periodic table ?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period ? Explain
Modern periodic table
The modern periodic table contains 118 elements arranged in the increasing order of their atomic numbers. The elements are divided into 18 groups and 7 periods. The elements in same group have same outer electronic configuration and elements in same period have same number of energy levels.
(a) Periodicity
When the elements are arranged in the increasing order of atomic numbers in the periodic table, elements with same properties occur at certain intervals. This is called periodicity. The periodic repetition of the properties is due to the recurrence of similar outer shell configurations in elements.
Each shell has a maximum occupancy of electrons. Due to this, when an orbital is filled electron moves to the outer shell causing the repetition of number of valence electrons.
Due to the periodicity in properties, there occurs a gradual change in properties across a period and along a group.
(b) Similarity in properties along a group
The elements in a group have same outer electronic configuration. Therefore, they have similar properties.
The number of valence electrons in the atom determines the valency of the atom which determines its chemical properties. Therefore, the elements of the same group have similar properties.
(c) Tendency to gain electrons across a period
The tendency of an atom to gain electron increases across a period.
In elements in the same period, the differentiating electron enter the same shell. This causes an increase in the effective nuclear charge on the valence electrons. Therefore, the nucleus pulls the electrons more causing a decrease in the atomic size. The increase in nuclear charge makes it easier to gain electrons. Therefore, the tendency to gain electron increases across a period.
Modern periodic table
The modern periodic table contains 118 elements arranged in the increasing order of their atomic numbers. The elements are divided into 18 groups and 7 periods. The elements in same group have same outer electronic configuration and elements in same period have same number of energy levels.
(a) Periodicity
When the elements are arranged in the increasing order of atomic numbers in the periodic table, elements with same properties occur at certain intervals. This is called periodicity. The periodic repetition of the properties is due to the recurrence of similar outer shell configurations in elements.
Each shell has a maximum occupancy of electrons. Due to this, when an orbital is filled electron moves to the outer shell causing the repetition of number of valence electrons.
Due to the periodicity in properties, there occurs a gradual change in properties across a period and along a group.
(b) Similarity in properties along a group
The elements in a group have same outer electronic configuration. Therefore, they have similar properties.
The number of valence electrons in the atom determines the valency of the atom which determines its chemical properties. Therefore, the elements of the same group have similar properties.
(c) Tendency to gain electrons across a period
The tendency of an atom to gain electron increases across a period.
In elements in the same period, the differentiating electron enter the same shell. This causes an increase in the effective nuclear charge on the valence electrons. Therefore, the nucleus pulls the electrons more causing a decrease in the atomic size. The increase in nuclear charge makes it easier to gain electrons. Therefore, the tendency to gain electron increases across a period.
