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Questions
Differentiate mass number from atomic number.
What is the difference between atomic number and mass number?
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Solution
| Sr. No. | Atomic number | Mass number |
| 1. | The number of electrons or protons in an atom is called the atomic number of that atom. | The number of protons and neutrons present in its nucleus is called the mass number of that atom. |
| 2. | It is represented by the letter Z. | It is represented by the letter ‘A’. |
| 3. | Example: Helium (He) has 2 protons and two electrons; hence, its atomic number will be 2. | Example: Sodium (Na) has 11 protons and 12 neutrons; hence, its mass number A = 11 + 12 = 23 |
RELATED QUESTIONS
The composition of the nuclei of two atomic species X and Y are given as under
| X | Y | |
| Protons | 6 | 6 |
| Neutrons | 6 | 8 |
Give the mass numbers of X and Y. What is the relation between the two species?
The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. What is its atomic number and mass number?
Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one:
- Forms an anion
- Forms a cation
- Has four electrons in its valence shell?
Match the atomic numbers 4,8,10,15 and 19 with the following:
Element which can form trivalent ion
Match the atomic numbers 4,8,10,15 and 19 with each of the following:
An element which does not form ion
If an atom ‘A’ has atomic number 19 and mass number 39, state –
- Its electronic configuration.
- The number of valence electrons it possesses.
Draw the atomic diagram of the following element showing the distribution of – protons, neutrons and the electrons in the various shell of the atom.
Phosphorus – \[\ce{^31_15P}\]
[The upper number represent the – mass number and the lower number represent the – atomic number e.g. calcium – mass number = 40, atomic number = 20]
Draw the structure of the following atoms showing the nucleus containing – protons, neutrons and the orbits with the respective electron:
Carbon [At. no. = 6, Mass no. = 12]
Compare the charge and mass of protons and electrons.
State the term for the following:
The amount of substance which contains the same number of units as the number of atoms in carbon-12.
