9th Class (CBSE) Science: Structure of the Atom

Question: If number of electrons in an atom is 8 and number of protons is also 8, then
(i) What is the atomic number of the atom? and
(ii) What is the charge on the atom?

Answer:

No. of electrons = 8

No. of protons = 8

(i)       Atomic number = no. of protons = 8

(ii) As,        Electrons = Protons

⊕ = Θ

∴     Atom is electrically neutral (No charge)

Question: With the help of given Table 4.1, find out the mass number of oxygen and sulphur atom.

Table: Composition of Atoms of the First Eighteen Elements with Electron Distribution in Various Shells

Answer:

Oxygen,                           No. of protons = 8

∴                                         No. of neutrons = 8

∴                                         Atomic number = 8

∴                                 Atomic mass number = P + N

= 8 + 8

= 16

Sulphur,                           No. of protons = 16

∴                                         No. of neutrons = 16

∴                                         Atomic number = 16

∴                                 Atomic mass number = P + N

= 16 + 16

= 32

Question: Write the electronic configuration of any one pair of isotopes and isobar.

Answer: Isotopes: Atoms of same element having same atomic number but different mass number.

 

Question: Compare the properties of electrons, protons and neutrons.

Answer: