Give the mass number of each of the following atoms:
a. beryllium with 5 neutrons
b. titanium with 26 neutrons
c. gallium with 39 neutrons
d. iron with 30 neutrons
The correct answer and explanation is:
To determine the mass number of an atom, you add the number of protons and neutrons. The mass number represents the total number of nucleons (protons and neutrons) in the nucleus of an atom.
a. Beryllium with 5 Neutrons:
Beryllium (Be) has an atomic number of 4, which means it has 4 protons. If it has 5 neutrons, the mass number is: Mass number=4 (protons)+5 (neutrons)=9\text{Mass number} = 4 \, (\text{protons}) + 5 \, (\text{neutrons}) = 9
Thus, the mass number of this beryllium atom is 9.
b. Titanium with 26 Neutrons:
Titanium (Ti) has an atomic number of 22, meaning it has 22 protons. With 26 neutrons, the mass number is: Mass number=22 (protons)+26 (neutrons)=48\text{Mass number} = 22 \, (\text{protons}) + 26 \, (\text{neutrons}) = 48
Therefore, the mass number of this titanium atom is 48.
c. Gallium with 39 Neutrons:
Gallium (Ga) has an atomic number of 31, indicating 31 protons. If it has 39 neutrons, the mass number is: Mass number=31 (protons)+39 (neutrons)=70\text{Mass number} = 31 \, (\text{protons}) + 39 \, (\text{neutrons}) = 70
Thus, the mass number of this gallium atom is 70.
d. Iron with 30 Neutrons:
Iron (Fe) has an atomic number of 26, so it has 26 protons. With 30 neutrons, the mass number is: Mass number=26 (protons)+30 (neutrons)=56\text{Mass number} = 26 \, (\text{protons}) + 30 \, (\text{neutrons}) = 56
Hence, the mass number of this iron atom is 56.
Explanation:
The mass number is not an actual mass value but a sum of the protons and neutrons in the nucleus. The number of protons (atomic number) defines the element, while the number of neutrons determines the isotope of that element. For example, titanium with 22 protons but 26 neutrons would be an isotope of titanium, different from the most common isotope with 22 protons and 23 neutrons (mass number 45). Each atom’s mass number varies depending on the number of neutrons, leading to different isotopes of the same element.