Atomic Number, Mass Number, and Isotopes - Worksheet | Distance ... - Free Printable

Problem Analysis and Solution

#### Q.6: What is the particle in a nucleus that determines the identity of the element?

- Key Concept: The identity of an element is determined by its atomic number, which is equal to the number of protons in the nucleus of an atom.
- Options:
- (a) Mass number: This is the total number of protons and neutrons in the nucleus.
- (b) Electron: Electrons do not determine the identity of an element; they contribute to chemical properties but not the atomic number.
- (c) Proton: The number of protons in the nucleus defines the atomic number, which uniquely identifies an element.
- (d) Neutron: While neutrons are present in the nucleus, their number varies among isotopes of the same element and does not determine the element's identity.

- Correct Answer: (c) Proton

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#### Q.7: The number of ________ can be calculated by subtracting its atomic number from its mass number.

- Key Concept: The mass number of an atom is the sum of the number of protons and neutrons in the nucleus. The atomic number is the number of protons. Therefore, the number of neutrons can be calculated as:
\[
\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}
\]

- Options:
- (a) photons: Photons are particles of light and are not related to the structure of the nucleus.
- (b) electrons: Electrons are outside the nucleus and do not affect the calculation of neutrons.
- (c) protons: The number of protons is given by the atomic number, not by subtracting atomic number from mass number.
- (d) neutrons: This is the correct particle, as explained above.

- Correct Answer: (d) neutrons

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#### Q.8: Complete the following chart.

The chart requires filling in the missing information for each element based on the given symbols and numbers. Let’s break it down step by step:

| Symbol | Element | Atomic Number | Number of Protons | Number of Neutrons | Mass Number |
|--------|---------|---------------|--------------------|---------------------|-------------|
| $^{17}_{8}$O | Oxygen | 8 | 8 | $17 - 8 = 9$ | 17 |
| $^{18}_{8}$O | Oxygen | 8 | 8 | $18 - 8 = 10$ | 18 |
| $^{63}_{27}$Co | Cobalt | 27 | 27 | $63 - 27 = 36$ | 63 |
| $^{222}_{88}$Ra | Radium | 88 | 88 | $222 - 88 = 134$ | 222 |
| $^{226}_{88}$Ra | Radium | 88 | 88 | $226 - 88 = 138$ | 226 |

- Explanation:
1. Symbol: The symbol indicates the element and its mass number and atomic number.
2. Element: Identified from the atomic number.
3. Atomic Number: Directly given or inferred from the symbol.
4. Number of Protons: Equal to the atomic number.
5. Number of Neutrons: Calculated as $\text{Mass Number} - \text{Atomic Number}$.
6. Mass Number: Directly given in the symbol.

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Final Answers:

- Q.6: $\boxed{\text{c) Proton}}$
- Q.7: $\boxed{\text{d) neutrons}}$
- Q.8: The completed chart is as follows:

| Symbol | Element | Atomic Number | Number of Protons | Number of Neutrons | Mass Number |
|--------|---------|---------------|--------------------|---------------------|-------------|
| $^{17}_{8}$O | Oxygen | 8 | 8 | 9 | 17 |
| $^{18}_{8}$O | Oxygen | 8 | 8 | 10 | 18 |
| $^{63}_{27}$Co | Cobalt | 27 | 27 | 36 | 63 |
| $^{222}_{88}$Ra | Radium | 88 | 88 | 134 | 222 |
| $^{226}_{88}$Ra | Radium | 88 | 88 | 138 | 226 |