# Exercise 1B

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Solutions, hints and answers can be found in the Solutions Page. It is strongly recommended that students do not look at the solutions until after completing or attempting to complete the problems. Going straight to the solutions will reduce the point of the exercises.

## 2.1

Both J.J Thomson and Ernest Rutherford had different understandings of how the structure of an atom actually looked like. What did each of them postulate about the structure of the atom?

## 2.2

Give the symbol of each ion for the following :

1. An ion with 20 protons, 20 neutrons, 18 electrons
2. An ion with 28 protons, 30 neutrons, 26 electrons
3. An ion with 28 protons, 30 neutrons, 24 electrons

## 2.3

Bromine has two stable isotopes: $$\ce{^{79}Br}$$ and $$\ce{^{81}Br}$$. The mass of 81Br is 80.92 u. The proportion of 79Br is 50.69%. The average atomic mass is 79.91 u. What is the mass of $$\ce{^{79}Br}$$?

## 2.4

Choose the true statement(s) and correct the wrong statement(s).

1. All particles in the nucleus of an atom are positively charged.
2. In an atom, electrons orbit around the nucleus.
3. The mass of the nucleus is approximately equals to the add-up mass of protons and neutrons.
4. The number of electrons equals to the number of neutrons.
5. Mass of an electron approximately equals to the mass of a proton.

Exercise 1B is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.