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Science Application: An atom consists of charged particles called electrons and protons. Each proton has a charge of +1 and each electron has a charge of –1. Remember number of electrons is equal to number of protons, while answering these questions:

(a) What is the charge on an atom?

(b) What will be the charge on an atom if it loses an electron?

(c) What will be the charge on an atom if it gains an electron?

Answer :

(a) Given that: An atom consists of,


Number of electrons = Number of protons


Let there be ‘a’ number of protons and ‘a’ number of electrons.


And, charge on 1 proton = +1


Then, charge on ‘a’ protons = 1 × a = a


Charge on electron = -1


Then, charge on ‘a’ electrons = -1 × a = -a


Total charge = Charge on ‘a’ protons + Charge on ‘a’ electrons


Total charge = a + (-a)


Total charge = 0


Thus, charge of an atom when there are equal number of electrons and protons is 0.


(b) Let the atom have ‘a’ number of electrons and ‘a’ number of protons.


If an atom loses an electron, it is left with (a – 1) electrons.


Number of protons = a


Now, charge on 1 electron = -1


Charge on ‘(a – 1)’ electrons = -1 × (a – 1)


Charge on ‘(a – 1)’ electrons = -(a – 1)


Charge on ‘(a – 1)’ electrons = (1 – a)


Charge on 1 proton = 1


Charge on ‘a’ protons = 1 × a


Charge on ‘a’ protons = a


Total charge on atom = (1 – a) + a


Total charge on atom = 1


(c) Let the atom have ‘a’ number of electrons and ‘a’ number of protons.


If an atom gains an electron, it becomes (a + 1) electrons.


Number of protons = a


Now, charge on 1 electron = -1


Charge on ‘(a + 1)’ electrons = -1 × (a + 1)


Charge on ‘(a + 1)’ electrons = -(a + 1)


Charge on 1 proton = 1


Charge on ‘a’ protons = 1 × a


Charge on ‘a’ protons = a


Total charge on atom = -(1 + a) + a


Total charge on atom = -1 – a + a


Total charge on atom = -1

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