There are six electrons, six protons and six neutrons in an atom of an element. What is the atomic mass number of the element?
12
Calculating Atomic Mass Number
The question asks for the atomic mass number of an element given the number of electrons, protons, and neutrons in its atom.
Understanding Atomic Structure
An atom is made up of three main subatomic particles:
- Protons: Positively charged particles found in the nucleus. The number of protons determines the element and is called the atomic number (\(Z\)).
- Neutrons: Neutrally charged particles also found in the nucleus.
- Electrons: Negatively charged particles that orbit the nucleus. In a neutral atom, the number of electrons equals the number of protons.
What is Atomic Mass Number?
The atomic mass number (often represented by \(A\)) is the total number of protons and neutrons in an atom's nucleus. It is essentially the mass of the nucleus (since protons and neutrons are much heavier than electrons).
The formula for atomic mass number is:
\[ A = \text{Number of Protons} + \text{Number of Neutrons} \]
Applying the Formula
We are given that the atom has:
- Number of electrons = 6
- Number of protons = 6
- Number of neutrons = 6
To find the atomic mass number, we use the number of protons and neutrons:
\[ A = 6 \text{ (protons)} + 6 \text{ (neutrons)} \]
\[ A = 12 \]
The number of electrons (6) is equal to the number of protons, confirming it's a neutral atom, but the number of electrons is not used in calculating the atomic mass number.
Conclusion
The atomic mass number of the element is 12.
| Particle | Number Given | Used for Mass Number? |
|---|---|---|
| Electrons | 6 | No |
| Protons | 6 | Yes |
| Neutrons | 6 | Yes |
Revision Table: Key Atomic Concepts
| Term | Definition |
|---|---|
| Atomic Number (\(Z\)) | Number of protons in the nucleus. Determines the element. |
| Mass Number (\(A\)) | Total number of protons and neutrons in the nucleus. |
| Isotope | Atoms of the same element (same number of protons) but with different numbers of neutrons (and thus different mass numbers). |
| Atomic Mass | Average mass of atoms of an element, taking into account the relative abundance of its isotopes. Usually expressed in atomic mass units (amu). |
Additional Information: Element Identification
The number of protons is what uniquely identifies an element. An element with 6 protons is always Carbon, regardless of the number of neutrons or electrons. The atomic number (number of protons) is a fundamental property of an element.
Atoms of the same element can have different numbers of neutrons; these are called isotopes. For example, Carbon-12 has 6 protons and 6 neutrons (mass number 12), while Carbon-14 has 6 protons and 8 neutrons (mass number 14). The question describes a Carbon-12 atom.
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