In introductory chemistry, what is the key difference between an atom and an ion?

• A. An atom contains neutrons but no electrons, while an ion contains electrons but no neutrons.
• B. An atom is electrically neutral, while an ion has a net charge because it has gained or lost electrons.
• C. An atom is a molecule, while an ion is a single proton.
• D. An atom always has more protons than electrons, while an ion always has more electrons than protons.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the definition of an atom. An atom is the smallest unit of an element that retains the chemical properties of that element. It consists of protons, neutrons, and electrons, and is electrically neutral because the number of protons equals the number of electrons.
2. Step 2: Understand the definition of an ion. An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge. This means the number of electrons is not equal to the number of protons.
3. Step 3: Identify the key difference. Since atoms have equal numbers of protons and electrons, they are electrically neutral. Ions, however, have an imbalance between protons and electrons, giving them a positive or negative charge.
4. Step 4: Review the incorrect options. For example, atoms do contain electrons and neutrons, so the statement that atoms contain neutrons but no electrons is false. Also, atoms are not molecules, and ions are not single protons.
5. Step 5: Summarize the key concept: The main difference is that an atom is electrically neutral, while an ion carries a net charge due to the loss or gain of electrons.