Bromine (Br) is atomic number 35. How many protons, neutrons, and electrons in a negative ion of Bromine-79 (Br” -79)?
35p. 44n, 35e
35p, 79n, 36e
79p, 35n,36e
35p, 44n, 36e
35p,44n, 34e
The correct answer and explanation is :
The correct answer is:
35 protons, 44 neutrons, 36 electrons.
Explanation:
- Protons: The number of protons in an atom is always equal to the atomic number, which identifies the element. Since Bromine (Br) has an atomic number of 35, this means that a neutral Bromine atom (with no charge) has 35 protons. In a negative ion, the number of protons does not change, so it remains 35.
- Neutrons: Neutrons are found in the nucleus of the atom, along with protons. The number of neutrons in an isotope can be determined by subtracting the atomic number from the atomic mass (or mass number). In this case, the isotope is Bromine-79 (Br-79), which has a mass number of 79.
To find the number of neutrons:
[
\text{Neutrons} = \text{Mass number} – \text{Atomic number}
]
[
\text{Neutrons} = 79 – 35 = 44
]
So, Bromine-79 has 44 neutrons. - Electrons: Electrons are negatively charged particles that orbit the nucleus of an atom. In a neutral atom, the number of electrons is equal to the number of protons. However, in the case of an ion, the number of electrons can be different from the number of protons. Since the problem specifies a “negative ion” (Br⁻), it means the atom has gained one extra electron compared to the neutral atom. In a neutral Bromine atom, there are 35 electrons (equal to the number of protons). In a negative ion (Br⁻), there is one additional electron, so the number of electrons becomes:
[
35 (\text{electrons in neutral Br}) + 1 = 36 \text{ electrons}.
]
Therefore, the negative ion of Bromine-79 (Br⁻) has 36 electrons.
Summary:
- Protons = 35 (same for both neutral atom and ion)
- Neutrons = 44 (mass number 79 minus atomic number 35)
- Electrons = 36 (one more electron than the neutral atom due to the negative charge)