Naming Common Ionic Compounds — Fast, Fun, and Actually Useful

You already learned how the periodic table tells you how many valence electrons an atom has and how ionic versus covalent bonds form. Now we turn those tools into language: how to name the ionic compounds you meet in the lab, in the news, and in neutralization reactions from acids and bases.

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Why this matters (quick reminder)

Knowing names lets you: recognize salts formed when acids neutralize bases (remember HCl + NaOH → NaCl + H2O?), write correct formulas that obey conservation of charge, and communicate safely in chemistry class and beyond.

Think of naming as the address label for a compound. If you get the name right, you can rebuild the formula, predict behavior, and avoid accidentally pouring sodium chloride into your ethanol (don’t do that).

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Core naming rules (the cheat sheet)

1) Metal + nonmetal (simple ions)

• Cation first (metal), then anion.
• For a single-element anion, change the ending to -ide.

Examples:

• NaCl → sodium chloride
• MgO → magnesium oxide
• Al2O3 → aluminium oxide (US: aluminum oxide)

(Micro explanation: Metals form positive ions (cations), nonmetals form negative ions (anions). Name the cation, then the anion with -ide.)

2) Compounds with polyatomic ions

Some charged groups of atoms behave as single units — polyatomic ions. Use the polyatomic ion name unchanged.

Common ones to memorize (you’ll see these a lot):

• NO3- : nitrate
• SO4^2- : sulfate
• CO3^2- : carbonate
• OH- : hydroxide
• NH4+ : ammonium

Examples:

• NaNO3 → sodium nitrate
• CaCO3 → calcium carbonate
• NH4Cl → ammonium chloride

3) Transition metals (variable charges)

Many transition metals have more than one common charge. Use Roman numerals to show the metal’s charge in the name.

Examples:

• FeCl2 → iron(II) chloride (Fe2+)
• FeCl3 → iron(III) chloride (Fe3+)
• CuO → copper(II) oxide (Cu2+)

(Micro explanation: Roman numerals are required when a metal can form multiple cations; they tell you the exact charge so you can write the correct formula.)

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From name → formula: step-by-step (use conservation of charge)

1. Identify the cation and anion from the name. Write their charges (use periodic table / memory for polyatomic ions).
2. Balance total positive and negative charge so the net charge = 0 (conservation of charge).
3. Write the formula with subscripts showing how many of each ion. Use parentheses around polyatomic ions when needed.

Example 1 — "magnesium nitrate":

• Mg2+ and NO3-
• Need two NO3- to balance one Mg2+ (2 × -1 = -2)
• Formula: Mg(NO3)2

Example 2 — "aluminium sulfate":

• Al3+ and SO4^2-
• Least common multiple of 3 and 2 is 6 → need 2 Al3+ (total +6) and 3 SO4^2- (total -6)
• Formula: Al2(SO4)3

(Side note: You never change ion charges; you only change how many of each ion are needed to cancel charges.)

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From formula → name: reverse the steps

1. Split formula into ions.
2. Name the cation (if transition metal, determine charge, use Roman numeral if needed).
3. Name the anion (-ide for monoatomic, or the polyatomic name).

Examples:

• K2SO4 → potassium sulfate (K+ and SO4^2-)
• Cu(NO3)2 → copper(II) nitrate (Cu2+ with two NO3-)

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Naming salts from neutralization (connect to acids/bases)

When an acid and a base neutralize, the H+ from the acid and the OH- from the base make water; the remaining ions form a salt.

Examples tied to your previous lesson on acids and pH:

• HCl (hydrochloric acid) + NaOH (sodium hydroxide) → NaCl (sodium chloride) + H2O
  • Name of salt: sodium chloride
• H2SO4 (sulfuric acid) + 2 NaOH → Na2SO4 (sodium sulfate) + 2 H2O
  • Name of salt: sodium sulfate

Important: the acid’s anion gives the salt’s anion (e.g., sulfate from sulfuric acid, nitrate from nitric acid). The base supplies the metal cation.

Also: some salts affect pH (remember that salts of weak acids or bases can change solution pH). Knowing the salt’s name helps predict that behavior.

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Quick common mistakes and how to avoid them

• Saying "sodium chloride" when the formula is Na2Cl — impossible. Always check charge balance.
• Forgetting parentheses for multiple polyatomic ions: Mg(NO3)2, not MgNO32.
• Not using Roman numerals with transition metals: "iron chloride" is vague — use iron(II) chloride or iron(III) chloride.
• Mixing up -ate and -ite. These are related polyatomic ions (e.g., sulfate SO4^2- vs sulfite SO3^2-); memorize common pairs.

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Practice — try these (answers follow)

1. Name: KBr
2. Formula: aluminium hydroxide
3. Name: CuSO4
4. Formula: iron(III) oxide
5. Name: (NH4)2CO3
6. Formula: calcium phosphate

Answers

1. potassium bromide
2. Al(OH)3 (Al3+ + 3 OH-)
3. copper(II) sulfate (Cu2+ with SO4^2-)
4. Fe2O3 (Fe3+ with O2-)
5. ammonium carbonate
6. Ca3(PO4)2 (Ca2+ and PO4^3- → need 3 Ca2+ and 2 PO4^3-)

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Key takeaways — stick these in your brain

• Cation first, anion second. Monoatomic anions end in -ide. Polyatomic ions keep their names.
• Balance charges — conservation of charge is the rule that builds correct formulas.
• Roman numerals for metals with multiple charges.
• Neutralization reactions make salts — name the salt by combining the cation from the base and the anion from the acid.

"If you can read the periodic table and balance a simple equation, you can name almost any ionic compound you’ll see in Grade 10 chemistry. Practice = instant confidence."

Go try the practice problems with a friend — or explain the rules to someone who doesn’t like chemistry (try your cat). If they understand, you do too.