Calcium is element number 20 on the Periodic Table. As an ion it has a +2 charge. How many electrons does a calcium ion have?A20B4C22D18

Break Down the Problem

1. Identify the atomic number of calcium.
2. Determine the charge of the calcium ion.
3. Calculate the number of electrons in the calcium ion based on its atomic number and charge.

Relevant Concepts

• The atomic number of an element indicates the number of protons and, in a neutral atom, also the number of electrons.
• A positive charge indicates a loss of electrons: for a +2 charge, 2 electrons are lost.

Analysis and Detail

1. Calcium (Ca) has an atomic number of 20, which means in a neutral state it has 20 protons and 20 electrons.
2. As a calcium ion ($\text{Ca}^{2+}$), it has a +2 charge. This means it has lost 2 electrons.
3. Thus, the number of electrons in the calcium ion is calculated as follows: $\text{Electrons in } \text{Ca}^{2+} = \text{Electrons in neutral Ca} - \text{Electrons lost}$ $\text{Electrons in } \text{Ca}^{2+} = 20 - 2 = 18$

Verify and Summarize

The calculations confirm that the calcium ion has 18 electrons, as the +2 charge indicates it has lost 2 electrons from the neutral state.

Final Answer

D) 18