This question is about atoms and isotopes. 4
(a) Atoms contain protons, neutrons and electrons. A lithium atom has the symbol 7 3 Li Explain, in terms of sub-atomic particles, why the mass number of this lithium atom is 7. Because this lithium atom has 3 protons and 4 neutrons mass number is total of neutrons and protons
The Correct Answer and Explanation is:
To explain why the mass number of the lithium atom is 7, represented by the symbol ( ^7_3Li ), we first need to understand the basic structure of an atom and the role of subatomic particles, which are protons, neutrons, and electrons.
- Understanding Atomic Structure: Atoms are composed of three primary types of subatomic particles:
- Protons: Positively charged particles found in the nucleus of the atom. The number of protons defines the element and is known as the atomic number.
- Neutrons: Neutral particles that also reside in the nucleus. Neutrons contribute to the mass of the atom but do not affect its chemical properties.
- Electrons: Negatively charged particles that orbit the nucleus in electron shells. Electrons are involved in chemical bonding but have negligible mass compared to protons and neutrons.
- Mass Number Definition: The mass number of an atom is the total count of protons and neutrons in its nucleus. This number reflects the atom’s mass because protons and neutrons are significantly more massive than electrons.
- Analyzing Lithium ( ^7_3Li ): In the case of lithium, the notation ( ^7_3Li ) indicates that this particular lithium atom has:
- 3 Protons: The lower number (3) indicates the atomic number of lithium, which defines it as lithium since it has three protons.
- 4 Neutrons: To find the number of neutrons, we subtract the number of protons from the mass number. Since the mass number is 7 (the upper number), the calculation is as follows:
[
\text{Neutrons} = \text{Mass Number} – \text{Protons} = 7 – 3 = 4
]
- Conclusion: Therefore, the mass number of the lithium atom is 7 because it has a total of 3 protons and 4 neutrons. This combination yields the mass number, which is a fundamental concept in understanding atomic mass and the identity of elements. Thus, the lithium atom, represented as ( ^7_3Li ), showcases the relationship between protons, neutrons, and mass number in atomic structure.