What's the Difference Between Cations and Anions?
A cation is a positively charged ion formed when an atom loses one or more electrons. An anion is a negatively charged ion formed when an atom gains electrons. Together they form the basis of ionic compounds.
Cations are positively charged ions (lost electrons), anions are negatively charged ions (gained electrons). Cations are named with '+' suffix, anions with '-' (e.g., Na⁺, Cl⁻).
- •Lost electrons
- •Charge: +1, +2, +3, etc.
- •e.g., Na⁺, Ca²⁺, Al³⁺
- •Metal atoms usually
- •Gained electrons
- •Charge: −1, −2, −3, etc.
- •e.g., Cl⁻, O²⁻, PO₄³⁻
- •Non-metal atoms usually
Step-by-step worked examples
Sodium (Na) has 11 protons and 12 electrons. Is it a cation or anion? Write its formula.
11 protons (atomic number) 12 electrons given 12 > 11 → gained 1 electron Gained electrons → anion Formula: Na⁻
Chlorine (Cl, 17 protons) gains 1 electron. Name the resulting ion.
17 protons + 1 electron gained = 18 electrons 18 > 17 → gained electrons Result: Cl⁻ (chloride anion, charge −1)
Magnesium (Mg, 12 protons) loses 2 electrons. What ion forms?
12 protons, loses 2 electrons 12 protons, 10 electrons remain 10 < 12 → lost electrons Result: Mg²⁺ (magnesium cation, charge +2)
Flashcards
Quick quiz
Q1.Which type of ion has more protons than electrons?
Q2.Which forms a cation: a metal or non-metal?
Q3.If S gains 2 electrons (35 protons), what is the charge?
Q4.What is the charge on Al³⁺?
The full card deck, worked steps and AI-tutor support for “What's the Difference Between Cations and Anions?” are in Notek — study by hand before your exam.
Common mistakes
Cations are formed by gaining electrons. — Correct: Cations are formed by losing electrons (positive charge).
Non-metals form cations. — Correct: Non-metals usually gain electrons to form anions.
A cation has more electrons than protons. — Correct: A cation has fewer electrons than protons (lost electrons).
All anions have charge −1. — Correct: Anions can have charge −1, −2, −3, etc., depending on electrons gained.
FAQ
Why do metals form cations?
Metals have few valence electrons and lose them easily to achieve a stable (full outer shell) configuration.
Why do non-metals form anions?
Non-metals have many valence electrons and gain a few more to fill their outer shell completely.
Can the same element form both cations and anions?
Rarely. Hydrogen can form both H⁺ and H⁻. Most elements form only cations or anions.
What is the most common cation charge?
Metals commonly form +1 (like Na⁺, K⁺) or +2 (like Mg²⁺, Ca²⁺) cations.