Atomic Structure Revision Questions and Answers (O level Chemistry)
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Question 1
The table shows some information about six particles.
- Complete the table.
- What is meant by the term isotopes?
- Identify two atoms which are isotopes of the same element.
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 |
Solution 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.
- 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.
- 35Cl and 37Cl
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 |
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