Atomic Structure Revision Questions and Answers (O level Chemistry)

Atomic Structure Revision Questions and Answers (O level Chemistry)

Question 1

The table shows some information about six particles.

1. Complete the table.

Particle	Proton (atomic) number	Number of neutrons	Number of electrons
35Cl	17	18	………
………..	17	20	17
39K+	19	………	18
79Br–	………	44	36
81Br	35	………	35
………..	37	48	36

2. 1. What is meant by the term isotopes?
   2. Identify two atoms which are isotopes of the same element.

Solution 1

1. Explanation on how to fill the table
• First row – Number of electrons = number of protons in a neutral atom. Therefore if ³⁵Cl has a proton number of 17, it means that it has 17 protons and 17 electrons.
• Second row – The proton number is 17, which means the element is Chlorine. However it has 20 Neutrons which means the nucleon number (protons + electrons) is 37. Therefore the element is ³⁷Cl.
• Third row – ³⁹K⁺ is a positively charged Potassium ion. A positively charged ion has a deficiency of electrons when compared to the neutral atom, but however the number of protons is the same. The number of neutrons of an ion (or atom) = Nucleon number – Proton number = 39 – 19 = 20.
• Fourth row – A ⁷⁹Br^– ion has an excess of 1 electron, hence its -1 charge, which means the number of protons = number of electrons – 1 = 36 – 1 = 35.
• Fifth row – Number of neutrons = nucleon number – proton number = 79 – 35 = 46.
• Sixth row – On the periodic table, element with proton number 37 is Rb. In the table above, there is a deficiency of 1 electron, which makes it an ion of charge +1.

Particle	Proton (atomic) number	Number of neutrons	Number of electrons
35Cl	17	18	17
37Cl	17	20	17
39K+	19	20	18
79Br–	35	44	36
81Br	35	46	35
85Rb+	37	48	36

2. 1. Either of the following:
   • Atoms with same number of protons but different number of neutrons.
   • Atoms with same atomic number but different nucleon number.
   • Atoms of the same element with different number of neutrons.
   2. ³⁵Cl and ³⁷Cl