IMAT Chemistry · Free notes

Inorganic Compounds and Their Names

Inorganic Compounds and Nomenclature has 9 past questions since 2011, and the ministry papers from 2023 on have asked 4 of them. Every one of them is recall plus a quick charge balance: no long calculations, but no partial credit for a half-remembered ending either. The ministry papers lean on classification, asking what family a compound belongs to and how an oxide behaves in water. Learn the ion charges and the naming endings until they are automatic, and these become some of the fastest marks in the Chemistry section.

The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.

IMAT home All formulas on one page

Subtopic notes

Formula & revision sheet

4 formulas · 6 reference tables · 11 gotchas across all subtopics — the exam-eve cheat-sheet

Oxidation Numbers, Common Ions and Writing Formulas

Formulas (2)

Rules for assigning oxidation numbers · Sum of oxidation numbers $\sum (\text{number of atoms} \times \text{oxidation number}) = \text{overall charge}$
Writing a correct formula by balancing charges · Charge balance $a \times (\text{cation charge}) + b \times (\text{anion charge}) = 0$

Reference tables (1)

Common ions and their charges12 rows

Name	Formula	Charge
Ammonium	$\mathrm{NH_4^+}$	1+
Hydroxide	$\mathrm{OH^-}$	1−
Nitrate / nitrite	$\mathrm{NO_3^-}$ / $\mathrm{NO_2^-}$	1−
Hydrogen carbonate	$\mathrm{HCO_3^-}$	1−
Hydrogen sulfate	$\mathrm{HSO_4^-}$	1−
Ethanoate (acetate)	$\mathrm{CH_3COO^-}$	1−
Permanganate	$\mathrm{MnO_4^-}$	1−
Cyanide	$\mathrm{CN^-}$	1−
Carbonate	$\mathrm{CO_3^{2-}}$	2−
Sulfate / sulfite	$\mathrm{SO_4^{2-}}$ / $\mathrm{SO_3^{2-}}$	2−
Chromate / dichromate	$\mathrm{CrO_4^{2-}}$ / $\mathrm{Cr_2O_7^{2-}}$	2−
Phosphate	$\mathrm{PO_4^{3-}}$	3−

Watch out for (4)

An element in its free state is always zero
→ Rules for assigning oxidation numbers
Hydrogen is negative in metal hydrides
→ Rules for assigning oxidation numbers
Carbonate is 2−, hydrogen carbonate is 1−
→ Common ions and their charges
Brackets matter: Ca(OH)₂ is not CaOH₂
→ Writing a correct formula by balancing charges

Oxides, Hydroxides, Acids, Hydrides and Salts

Formulas (1)

Oxides with water: hydroxides and oxoacids · Oxides and water $\text{metal oxide} + \mathrm{H_2O} \rightarrow \text{hydroxide} \qquad \text{non-metal oxide} + \mathrm{H_2O} \rightarrow \text{oxoacid}$

Reference tables (3)

Basic, acidic, amphoteric and neutral oxides4 rows

Type	Formed by	Behaviour	Examples
Basic	Metals, especially Groups 1 and 2	Neutralises acids; with water gives a hydroxide	$\mathrm{Na_2O}$ , $\mathrm{K_2O}$ , CaO, MgO, CuO
Acidic	Non-metals	Neutralises bases; with water gives an oxoacid	$\mathrm{CO_2}$ , $\mathrm{SO_2}$ , $\mathrm{SO_3}$ , $\mathrm{NO_2}$ , $\mathrm{P_4O_{10}}$ , $\mathrm{SiO_2}$
Amphoteric	Metals near the metal and non-metal border	Reacts with both acids and bases	$\mathrm{Al_2O_3}$ , ZnO, PbO
Neutral	A few non-metals	Reacts with neither acids nor bases	CO, NO, $\mathrm{N_2O}$

Silicon dioxide is acidic although it does not dissolve in water: it reacts with hot concentrated alkali.

Binary acids, oxoacids, hydroxides and hydrides5 rows

Class	Made of	Examples
Binary acid (hydracid)	H + one non-metal	HCl, HBr, HF, $\mathrm{H_2S}$
Oxoacid	H + non-metal + O	$\mathrm{H_2SO_4}$ , $\mathrm{HNO_3}$ , HClO, $\mathrm{H_3PO_4}$ , $\mathrm{H_2CO_3}$
Hydroxide	Metal ion + $\mathrm{OH^-}$	NaOH, $\mathrm{Ca(OH)_2}$ , $\mathrm{Al(OH)_3}$
Metal hydride	Metal + H (H is $-1$ )	NaH, $\mathrm{CaH_2}$ , LiH
Non-metal hydride	Non-metal + H (H is $+1$ )	$\mathrm{CH_4}$ , $\mathrm{NH_3}$ , $\mathrm{H_2O}$

Salts: normal, acid, basic and hydrated4 rows

Type	Contains	Examples
Normal salt	No replaceable H left	NaCl, $\mathrm{K_2SO_4}$ , $\mathrm{CaCO_3}$ , $\mathrm{CH_3COONa}$
Acid salt	Anion still carries acidic H	$\mathrm{NaHCO_3}$ , $\mathrm{NaHSO_4}$ , $\mathrm{KH_2PO_4}$
Basic salt	$\mathrm{OH^-}$ as well as another anion	Mg(OH)Cl, $\mathrm{Cu_2(OH)_2CO_3}$
Hydrated salt	Water of crystallisation	$\mathrm{CuSO_4 \cdot 5H_2O}$

Watch out for (4)

Not every non-metal oxide is acidic
→ Basic, acidic, amphoteric and neutral oxides
The acid keeps the oxidation number of its oxide
→ Oxides with water: hydroxides and oxoacids
An acid is not an oxide, and a hydroxide is not an acid
→ Binary acids, oxoacids, hydroxides and hydrides
Hydrogen in a formula does not make an acid salt
→ Salts: normal, acid, basic and hydrated

IUPAC and Traditional Names of Inorganic Compounds

Formulas (1)

From name to formula and from formula to name · Charge on each metal ion $\text{charge on each cation} = \frac{\text{number of anions} \times |\text{anion charge}|}{\text{number of cations}}$

Reference tables (2)

Naming metal compounds and binary covalent compounds7 rows

Formula	Stock (IUPAC) name	Traditional name
$\mathrm{FeCl_2}$	iron(II) chloride	ferrous chloride
$\mathrm{FeCl_3}$	iron(III) chloride	ferric chloride
$\mathrm{Cu_2O}$	copper(I) oxide	cuprous oxide
CuO	copper(II) oxide	cupric oxide
$\mathrm{SnCl_4}$	tin(IV) chloride	stannic chloride
PbO	lead(II) oxide	plumbous oxide
$\mathrm{Hg_2Cl_2}$	mercury(I) chloride	mercurous chloride

Oxoacids and oxoanions: hypo-, -ous, -ic, per- and -ite, -ate11 rows

Acid	Acid name	Anion	Anion name	Oxidation number
HClO	hypochlorous acid	$\mathrm{ClO^-}$	hypochlorite	Cl +1
$\mathrm{HClO_2}$	chlorous acid	$\mathrm{ClO_2^-}$	chlorite	Cl +3
$\mathrm{HClO_3}$	chloric acid	$\mathrm{ClO_3^-}$	chlorate	Cl +5
$\mathrm{HClO_4}$	perchloric acid	$\mathrm{ClO_4^-}$	perchlorate	Cl +7
$\mathrm{H_2SO_3}$	sulfurous acid	$\mathrm{SO_3^{2-}}$	sulfite	S +4
$\mathrm{H_2SO_4}$	sulfuric acid	$\mathrm{SO_4^{2-}}$	sulfate	S +6
$\mathrm{HNO_2}$	nitrous acid	$\mathrm{NO_2^-}$	nitrite	N +3
$\mathrm{HNO_3}$	nitric acid	$\mathrm{NO_3^-}$	nitrate	N +5
$\mathrm{H_3PO_4}$	phosphoric acid	$\mathrm{PO_4^{3-}}$	phosphate	P +5
$\mathrm{H_2CO_3}$	carbonic acid	$\mathrm{CO_3^{2-}}$	carbonate	C +4
HCl	hydrochloric acid	$\mathrm{Cl^-}$	chloride	Cl −1

Watch out for (3)

-ous and -ic on a metal give its charge, not the anion
→ Naming metal compounds and binary covalent compounds
-ite is the lower oxidation state, not the higher
→ Oxoacids and oxoanions: hypo-, -ous, -ic, per- and -ite, -ate
Work out the metal's charge from the anion first
→ From name to formula and from formula to name

PYQ weightage by concept

10 concepts · 0 PYQs — where the marks actually sit, so you know what to drill first

Oxidation Numbers, Common Ions and Writing Formulas0 PYQs · 0%

Concept	PYQs	Share
Rules for assigning oxidation numbersfoundation	—	—
Common ions and their chargesfoundation	—	—
Writing a correct formula by balancing chargesfoundation	—	—

Oxides, Hydroxides, Acids, Hydrides and Salts0 PYQs · 0%

Concept	PYQs	Share
Basic, acidic, amphoteric and neutral oxidesfoundation	—	—
Oxides with water: hydroxides and oxoacidsfoundation	—	—
Binary acids, oxoacids, hydroxides and hydridesfoundation	—	—
Salts: normal, acid, basic and hydratedfoundation	—	—

IUPAC and Traditional Names of Inorganic Compounds0 PYQs · 0%

Concept	PYQs	Share
Naming metal compounds and binary covalent compoundsfoundation	—	—
Oxoacids and oxoanions: hypo-, -ous, -ic, per- and -ite, -atefoundation	—	—
From name to formula and from formula to namefoundation	—	—