Chemical Bonding: Atomic size, anionic size, ionization energy,

Question 6.9: The atomic size of an atom cannot be determined precisely. Why?

Answer: The atomic size of an atom cannot be determined precisely due to following reasons.

1.There is no sharp boundary of an atom.

2. The probability (chances) of finding an electron never becomes zero even at large distance from the nucleus.

3. Electron cloud is affected by neighboring atoms, therefore, size of atom may change from one compound to an other compound.

Question 6.10: Why the anionic radius is larger than parent atom?

Answer: When a neutral atom gains one or more electrons, it becomes a negative ion. The radius of an anion is larger than the parent due to two reasons. An addition of one or more electrons in the shell of a neutral atom enhances repulsion between the electrons which causes the shell expansion. For example, radius of fluorine atom (F) is 72 pm and that of fluoride ion (F-) is 136 pm.

Question 6.11: What is meant by ionization and ionization energy? What are units of ionization energy? What are factors which affect the ionization energy?

Answer: The process in which a neutral atom is converted into an ion is called ionization energy. The ionization energy of an element may be defined as ‘’minimum energy required to remove an electron from gaseous atom (isolated atom) to form a cation’’.

SI units: Kj/mol

Example: Na ----->Na+ e- H = - 396 Kj/mol

Factors: The ionization energy depends upon the following factors.

1. Atomic size of atom (Greater the size of atom, smaller the ionization energy and vice versa).

2. Nuclear charge or proton number of an atom(Greater the nuclear charge, higher the ionization energy and vice versa).

3. Shielding effect of inner electrons (Greater inner shell electrons, greater the shielding effect and lower the ionization energy).

4. Nature of orbital (for a given shell, decreasing order of ionization energy is s>p>d>f).

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