Question

Q.5 Give reasons for the following: 1.Occurrence of characteristic properties of elements takes place at definite intervals in the modern periodic table. 2. Properties of elements are periodic functions of their atomic numbers and not atomic weights.
3. Atomic size of an element depends on the nuclear charge of that element.
4. Down a group electronegativity should increase with increase in nuclear charge but it is seen that the electronegativity decreases.
5. If combining atoms have nearly similar electronegativities the bond between them is covalent. ​

Answer 1

Answer:

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Answer 2

Periodic classification of elements.

Explanation:

• In modern periodic table, repetition of characteristic properties of elements after a regular intervals is due to repetition of same outermost shell electronic configuration of elements  after a regular interval with a difference of 2,8,18and 32 in atomic numbers.
• Atomic number is the basis of classification of physical and chemical properties not atomic masses. This is because properties of elements depends upon valence shell configuration (i.e. number of electrons). Atomic number of elements is equal to no. of protons or electrons.
• Nuclear charge means the tendency to hold the electrons tightly by the nucleus. More will be the attraction between nucleus and electrons, more will be the nuclear charge. Hence, smaller will be the atomic size.
• As going down the group, increasing number of shell factor dominates over nuclear charge factor which means as number of shell increases tendency to donate electrons increases. Hence, electronegativity decreases.
• Two atoms with same electronegativities will going to form covalent bond because donation and acceptance of electrons is not possible in case of atoms with same electronegativities. So, the bond will be formed by the mutual contribution of electrons ( i.e. sharing of electrons). Thus, form covalent bond.