How are the atomic number (Z) and mass number (A) related to each other?

Answer

To understand the relationship between atomic number (Z) and mass number (A), we can break it down into a few clear steps:

### Step 1: Define Atomic Number (Z)
The atomic number (Z) of an element is defined as the number of protons present in the nucleus of an atom. It also equals the number of electrons in a neutral atom.

### Step 2: Define Mass Number (A)
The mass number (A) is the total number of protons and neutrons in the nucleus of an atom. It gives an indication of the mass of the atom.

### Step 3: Relationship Between Mass Number and Atomic Number
The relationship between mass number (A), atomic number (Z), and the number of neutrons (N) can be expressed with the formula:
\[ A = Z + N \]
Where:
- A = Mass number
- Z = Atomic number
- N = Number of neutrons

### Step 4: Rearranging the Formula
From the formula \( A = Z + N \), we can also express the number of neutrons (N) as:
\[ N = A - Z \]
This shows how the mass number and atomic number are related through the number of neutrons.

### Conclusion
In summary, the atomic number (Z) indicates the number of protons in an atom, while the mass number (A) represents the total number of protons and neutrons. The relationship can be summarized by the equation \( A = Z + N \).

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