The atomic number of lithium is 3. How many neutrons does an atom of lithium have if it is represented by the symbol shown below?
A 2 neutrons
B 13 neutrons
C 4 neutrons
D 7 neutrons
The correct answer and explanation is :
The correct answer is C: 4 neutrons.
Here’s the explanation:
Lithium is an element with the atomic number 3, meaning it has 3 protons in its nucleus. In order to calculate the number of neutrons in an atom of lithium, we need to know its atomic mass (also known as the mass number).
The mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom. For lithium, the most common isotope is Lithium-7, which has an atomic mass of approximately 7 atomic mass units (amu).
Step-by-step explanation:
- Atomic number: The atomic number of lithium is 3, which means it has 3 protons in its nucleus.
- Mass number: The mass number of lithium in this case is 7, which is the sum of protons and neutrons in the nucleus.
- Calculating neutrons: To find the number of neutrons, we subtract the number of protons from the mass number:
[
\text{Neutrons} = \text{Mass number} – \text{Atomic number} = 7 – 3 = 4.
]
Therefore, an atom of lithium has 4 neutrons in its nucleus, making the correct answer C: 4 neutrons.
Additional Information:
There are other isotopes of lithium, such as Lithium-6 (with a mass number of 6), which would have 3 neutrons (since 6 – 3 = 3). However, the most common isotope of lithium is Lithium-7, which has 4 neutrons.
In summary, lithium with an atomic number of 3 and a mass number of 7 has 4 neutrons. This is the stable and most abundant form of lithium found in nature.