To calculate an ion's charge from its atomic number and mass number, you need to consider the number of protons and electrons in the ion.
Determine the number of protons: The atomic number of an element represents the number of protons in its nucleus. Therefore, the atomic number directly provides the number of protons in an atom.
Determine the number of electrons: In a neutral atom, the number of electrons is equal to the number of protons. However, if the ion is positively or negatively charged, the number of electrons will differ.
- For positively charged ions (cations): Subtract the charge (in units of positive charges, +) from the number of protons. For example, if the ion has a charge of +2, subtract 2 from the number of protons.
- For negatively charged ions (anions): Add the charge (in units of negative charges, -) to the number of protons. For example, if the ion has a charge of -1, add 1 to the number of protons.
Note: The mass number (or atomic mass) is not directly involved in determining the charge of an ion. It represents the total number of protons and neutrons in an atom but does not influence the ion's charge.
Once you determine the number of protons and electrons in the ion, the resulting charge corresponds to the excess or deficit of electrons. A positive charge (+) indicates a cation with fewer electrons than protons, while a negative charge (-) indicates an anion with more electrons than protons.
It's important to note that the charge of an ion can also be determined by other factors, such as its position in the periodic table and its electron configuration, which influence the tendency of an atom to gain or lose electrons.