Mass number is a fundamental property of atoms, representing the total number of protons and neutrons in the nucleus. Protons and neutrons each contribute one unit to the mass number, while electrons have negligible mass and therefore do not affect it. The mass number of an atom is always a whole number because it corresponds to the actual number of physical particles, namely protons and neutrons, present in the nucleus.
Why is Mass Number Always a Whole Number?
The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. It is always a whole number because the number of protons (atomic number) and the number of neutrons in an atom are both whole numbers.
Atomic Number
- The atomic number is the number of protons in an atom’s nucleus.
- It determines the element to which an atom belongs.
- It is unique for each element and cannot be changed without changing the element itself.
Number of Neutrons
- The number of neutrons in an atom’s nucleus is determined by the isotope of the element.
- Isotopes are different forms of the same element that have different numbers of neutrons.
- The number of neutrons can vary for a given element, but it must be a whole number.
Mathematical Explanation
The mass number of an atom can be represented by the following equation:
Mass Number = Atomic Number + Number of Neutrons
Since both atomic number and number of neutrons are whole numbers, the sum of these two numbers must also be a whole number.
Therefore, the mass number of an atom is always a whole number.
Table of Examples
The following table shows the atomic numbers, numbers of neutrons, and mass numbers for various isotopes of hydrogen and carbon:
| Isotope | Atomic Number | Number of Neutrons | Mass Number |
|---|---|---|---|
| Hydrogen-1 | 1 | 0 | 1 |
| Hydrogen-2 (deuterium) | 1 | 1 | 2 |
| Carbon-12 | 6 | 6 | 12 |
| Carbon-13 | 6 | 7 | 13 |
| Carbon-14 | 6 | 8 | 14 |
As you can see from the table, the mass numbers for all of these isotopes are whole numbers. This is because the sum of the atomic numbers and numbers of neutrons for each isotope is also a whole number.
Question 1:
Why is the mass number of an atom always a whole number?
Answer:
The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. Protons and neutrons are indivisible particles, so the mass number must also be an integer.
Question 2:
What determines the mass number of an element?
Answer:
The mass number of an element is determined by the number of protons in its nucleus, which is specific to each element.
Question 3:
How is the mass number related to the atomic number?
Answer:
The mass number of an atom is typically greater than its atomic number, which represents the number of protons in the nucleus. This difference is due to the presence of neutrons, which have no charge.
Well, there you have it, folks! Now you know why the mass number of an atom is always a whole number. It’s because it’s a count of the total number of protons and neutrons in the nucleus, and both protons and neutrons are indivisible particles. So, the next time you hear someone talking about the mass number of an atom, you can impress them with your newfound knowledge. Thanks for reading! Be sure to check back later for more exciting science tidbits.