09 Chemistry

Unlocking the Secrets of Chemical Communication

Chemistry has its own universal language of chemistry, a precise system of symbols, formulas, and equations that scientists use to communicate reactions, elements, and compounds. This language of chemistry includes chemical symbols, valency, molecular formulas, and balanced equations, all of which follow strict rules to ensure clarity and accuracy. By mastering the language of chemistry, students and researchers can decode complex reactions, predict product formations, and understand the composition of matter. From Dalton’s early symbols to modern IUPAC conventions, this language of chemistry bridges theory and experimentation, making it an essential foundation for scientific discovery. Whether balancing equations or calculating molecular masses, fluency in the language of chemistry is key to unlocking the mysteries of the chemical world.

SYLLABUS

(i) Symbol of an element; valency; formulae of radicals and formulae of compounds. Balancing of simple chemical equations.

Symbol – definition; symbols of the elements used often.
Valency – definition; hydrogen combination and number of valence electrons of the metals and non-metals; mono, di, tri and tetra valent elements.
Radicals – definition; formulae and valencies.
Compounds – name and formulae.
Chemical equation – definition and examples of chemical equations with one reactant and two or three products, two reactants and one product, two reactants and two products and two reactants and three or four products; balancing of equations (by hit and trial method).

(ii) Relative Atomic Masses (atomic weights) and Relative Molecular Masses (molecular weights): either standard H atom or 1/12th of carbon 12 atom.

Definitions
Calculation of Relative Molecular Mass and percentage composition of a compound.

Summary

1. What is Chemistry?

Chemistry is the science that studies matter—what it’s made of, its structure, and how it changes under different conditions.
Matter is made up of elements, which are pure substances that cannot be broken down further.

2. Atoms and Molecules

Atoms are the smallest particles of an element.
When atoms of the same type join, they form molecules.
Molecules can be:
- Monoatomic (1 atom, e.g., helium).
- Diatomic (2 atoms, e.g., oxygen O₂).
- Polyatomic (many atoms, e.g., sulphur S₈).

3. Compounds

When different elements combine, they form compounds (e.g., water H₂O, salt NaCl).
The smallest particle of a compound is a molecule.

4. Symbols of Elements

Elements are represented by symbols (e.g., O for oxygen, H for hydrogen).
Some symbols come from Latin names (see table below).

Element	Symbol	Latin Name
Gold	Au	Aurum
Silver	Ag	Argentum
Iron	Fe	Ferrum
Sodium	Na	Natrium
Potassium	K	Kalium

Chemical Symbols & Formulas – Easy Summary

1. What is a Chemical Symbol?

A symbol is a short way to write an element’s name (e.g., “S” for sulphur, “H” for hydrogen).
If two elements start with the same letter, we add a second small letter (e.g., “Co” for cobalt, “Cu” for copper).

2. Importance of Symbols

A symbol represents:
- The name of the element (e.g., “N” = nitrogen).
- One atom of that element.
- The atomic mass (e.g., “N” also means 14 atomic mass units).

3. Common Element Symbols

Element	Symbol	Element	Symbol
Magnesium	Mg	Hydrogen	H
Aluminium	Al	Nitrogen	N
Calcium	Ca	Oxygen	O
Chromium	Cr	Chlorine	Cl

4. Chemical Formulas

A formula shows atoms in a molecule using symbols (e.g., H₂O = water).
Numbers (subscripts) show how many atoms are present (e.g., CO₂ = 1 carbon + 2 oxygen atoms).
Big numbers before a formula = how many molecules (e.g., 2H₂O = two water molecules).

5. What Formulas Tell Us

The type and number of atoms (e.g., NH₄Cl = 1 nitrogen + 4 hydrogen + 1 chlorine).
The mass ratio (e.g., CO₂ has a mass of 12 + 16×2 = 44 atomic units).

Quiz Time! (MCQs with Answers)
1. Why does cobalt have the symbol “Co”?
a) It’s short for “coconut”
b) Two letters are needed because many elements start with “C” ✅
c) It’s a secret code
2. What does “H₂O” represent?
a) A single hydrogen atom
b) One water molecule (2 hydrogen + 1 oxygen) ✅
c) A helium molecule
3. If you see “2NaCl,” what does it mean?
a) Two atoms of sodium
b) Two molecules of salt (sodium chloride) ✅
c) A typo
4. Why is gold’s symbol “Au”?
a) It’s shiny like the sun (Aurum means “shining dawn” in Latin) ✅
b) Scientists liked the sound
c) It’s short for “awesome uranium”
5. What’s the mass of CO₂ if carbon=12 and oxygen=16?
a) 12
b) 28
c) 44 ✅ (12 + 16 + 16 = 44)

Funny Chemistry Jokes 🧪😂
Why did the chemist sit on his desk?
He wanted to find his solution!
What do you call a clown who’s in jail?
A sodium chloride! (NaCl = “salt” + “silly” pun!)
Why do chemists love nitrates?
Because they’re cheaper than day rates!
What did the scientist say when he found two helium atoms?
HeHe!
Why was the mole of oxygen so happy?
It made Avogadro’s number of friends!

Valency – Simplified Summary

1. What is Valency?

Valency is the combining power of an atom. It tells how many hydrogen atoms (or double the oxygen atoms) an element can bond with.
Example: Oxygen (O) has a valency of 2 because it combines with 2 hydrogen atoms to form water (H₂O).

2. Modern Definition

Valency = Number of electrons an atom can lose, gain, or share to become stable.
Metals (like Na, Mg) lose electrons → Positive valency.
Non-metals (like Cl, O) gain electrons → Negative valency.

3. Variable Valency

Some elements (e.g., Iron, Copper) show multiple valencies due to losing electrons from different shells.
Naming rule:
- Lower valency → “-ous” (e.g., Ferrous = Iron(II), Cu**+** = Cuprous).
- Higher valency → “-ic” (e.g., Ferric = Iron(III), Cu²+ = Cupric).

4. Examples of Valency

Element	Valency	Example Compound
Hydrogen (H)	1	H₂O
Oxygen (O)	2	CO₂
Nitrogen (N)	3	NH₃
Carbon (C)	4	CH₄
Iron (Fe)	2 or 3	FeO (Ferrous), Fe₂O₃ (Ferric)

Quiz Time! (MCQs on Valency)
1. What is the valency of nitrogen in NH₃?
a) 1
b) 3 ✅ (Correct! N bonds with 3 H atoms.)
c) 5
2. Why does iron show variable valency?
a) It’s magnetic
b) It loses electrons from different shells ✅ (Yes! Fe²⁺ and Fe³⁺ exist.)
c) It’s a non-metal
3. Cuprous (Cu⁺) and Cupric (Cu²⁺) differ in:
a) Color
b) Valency ✅ (Correct! “ous” = lower valency, “ic” = higher.)
c) Atomic mass
4. Which element always has a valency of 1?
a) Oxygen
b) Hydrogen ✅ (Right! H forms 1 bond, like in HCl.)
c) Carbon

Funny Jokes About Valency 😄
Why did the chemist break up with her boyfriend?
Because there was no valency—he couldn’t bond with her!
Why was the sodium ion (Na⁺) so confident?
Because it never lost its charge!
What did the Fe²⁺ say to the Fe³⁺?
“You’re so extra!” (Fe³⁺ has one more lost electron!)
Why do chemists love valency jokes?
Because they’re bonding!

Variable Valency – Simplified Summary

1. What is Variable Valency?

Some elements can change their valency (combining power) depending on the reaction.
This happens because they lose electrons from different electron shells to form ions.

2. Common Examples

Element	Lower Valency (-ous)	Higher Valency (-ic)
Iron (Fe)	Fe²⁺ (Ferrous)	Fe³⁺ (Ferric)
Copper (Cu)	Cu⁺ (Cuprous)	Cu²⁺ (Cupric)
Mercury (Hg)	Hg⁺ (Mercurous)	Hg²⁺ (Mercuric)
Lead (Pb)	Pb²⁺ (Plumbous)	Pb⁴⁺ (Plumbic)

3. Why Does It Happen?

Atoms may lose extra electrons from inner shells to form different ions.
Example: Iron can lose 2 electrons (Fe²⁺) or 3 electrons (Fe³⁺).

4. Naming Rules

Lower valency → Ends with “-ous” (e.g., Ferrous = Fe²⁺).
Higher valency → Ends with “-ic” (e.g., Ferric = Fe³⁺).
Modern naming uses Roman numerals (e.g., Iron(II) = Fe²⁺, Iron(III) = Fe³⁺).

Quiz Time! (MCQs on Variable Valency)
1. What is the valency of copper in Cu₂O?
a) 1 ✅ (Correct! Cuprous = Cu⁺.)
b) 2
c) 3
2. Why does iron show variable valency?
a) It’s magnetic
b) It loses electrons from different shells ✅ (Yes! Fe can lose 2 or 3 electrons.)
c) It’s a gas
3. What is the modern name for Fe³⁺?
a) Ferrous
b) Iron(II)
c) Iron(III) ✅ (Correct! Higher valency = “-ic” or Roman numeral III.)
4. Which element does NOT show variable valency?
a) Iron (Fe)
b) Sodium (Na) ✅ (Right! Na always has a valency of 1.)
c) Lead (Pb)

Funny Jokes About Variable Valency 😆
Why did Fe²⁺ break up with Fe³⁺?
Because Fe³⁺ was too charged for the relationship!
Why did the chemistry teacher love variable valency?
Because it made bonding more exciting!
What did Cuprous (Cu⁺) say to Cupric (Cu²⁺)?
“You’re always so extra!”
Why was Mercury (Hg) so unpredictable?
Because it kept changing its charge—just like its temperature!

Radicals – Simplified Summary

1. Definition of Radicals (Pink Section)

A radical is an atom or group of atoms that behaves as a single charged unit (positive or negative) in chemical reactions.
Example: In NaCl, Na⁺ (sodium ion) and Cl⁻ (chloride ion) are radicals that combine to form salt.

2. Types of Radicals

Simple Radicals: Single charged atoms (e.g., Na⁺, Cl⁻).
Compound Radicals: Groups of atoms with a net charge (e.g., NH₄⁺, SO₄²⁻).

3. Classification by Origin

Basic/Electropositive Radicals: Come from bases (e.g., Na⁺ from NaOH).
Acid/Electronegative Radicals: Come from acids (e.g., Cl⁻ from HCl).

4. Classification by Valency

Valency	Electropositive (Cations)	Electronegative (Anions)
Monovalent (1)	Na⁺, K⁺, NH₄⁺	Cl⁻, NO₃⁻, OH⁻
Divalent (2)	Ca²⁺, Mg²⁺, Fe²⁺	SO₄²⁻, CO₃²⁻, O²⁻
Trivalent (3)	Al³⁺, Fe³⁺	PO₄³⁻, BO₃³⁻
Tetravalent (4)	Pb⁴⁺, Sn⁴⁺	C⁴⁻, Fe(CN)₆⁴⁻

5. Complete Tables of Radicals

Table of Electropositive Radicals (Cations)

Valency	Radical	Symbol	Example Source
Monovalent (9)	Sodium	Na⁺	NaOH
	Potassium	K⁺	KOH
	Ammonium	NH₄⁺	NH₄OH
Divalent (13)	Calcium	Ca²⁺	Ca(OH)₂
	Magnesium	Mg²⁺	Mg(OH)₂
	Iron(II)	Fe²⁺	Fe(OH)₂
Trivalent (6)	Aluminium	Al³⁺	Al(OH)₃
	Iron(III)	Fe³⁺	Fe(OH)₃
Tetravalent (3)	Lead(IV)	Pb⁴⁺	Pb(OH)₄

Table of Electronegative Radicals (Anions)

Valency	Radical	Symbol	Example Source
Monovalent (20)	Chloride	Cl⁻	HCl
	Nitrate	NO₃⁻	HNO₃
	Hydroxide	OH⁻	NaOH
Divalent (15)	Sulphate	SO₄²⁻	H₂SO₄
	Carbonate	CO₃²⁻	H₂CO₃
	Oxide	O²⁻	–
Trivalent (8)	Phosphate	PO₄³⁻	H₃PO₄
	Borate	BO₃³⁻	H₃BO₃
Tetravalent (2)	Carbide	C⁴⁻	–

6. Key Properties

Radicals cannot exist freely – they always pair to form neutral compounds.
In water, salts split into radicals (e.g., NaCl → Na⁺ + Cl⁻).
The valency determines how radicals combine (e.g., Ca²⁺ + 2Cl⁻ → CaCl₂).

Quiz Time! (MCQs on Radicals)
1. Which is a compound radical?
a) Na⁺
b) SO₄²⁻ ✅ (Correct! It’s a group of atoms with a charge.)
2. What valency is Al³⁺?
a) 1
b) 3 ✅ (Right! The superscript “3+” shows its valency.)
3. Which radical comes from HNO₃?
a) CO₃²⁻
b) NO₃⁻ ✅ (Yes! Nitrate is from nitric acid.)
4. How many Cl⁻ ions balance Ca²⁺?
a) 1
b) 2 ✅ (Correct! Ca²⁺ needs two monovalent Cl⁻ ions.)

Funny Jokes About Radicals 😄
Why did Na⁺ and Cl⁻ get married?
Their bond was unbreakably ionic!
Why was SO₄²⁻ a bad comedian?
Its jokes were too sulfuric!
What did NH₄⁺ say to OH⁻?
“You’re OH-some!”
Why did PO₄³⁻ refuse to fight?
It had three charges to defend itself!

Here are the properly formatted tables for your reference:

Table showing List of some common electrovalent positive ions (basic radicals)

Monovalent electropositive	Divalent electropositive	Trivalent electropositive
1. Ammonium NH₄⁺	1. Argentic [Silver(II)] Ag²⁺	1. Aluminium Al³⁺
2. Aurous [Gold (I)] Au⁺	2. Barium Ba²⁺	2. Arsenic As³⁺
3. Argentous [Silver (I)] Ag⁺	3. Calcium Ca²⁺	3. Auric [Gold (III)] Au³⁺
4. Cuprous [Copper (I)] Cu⁺	4. Cupric [Copper(II)] Cu²⁺	4. Bismuth Bi³⁺
5. Hydrogen H⁺	5. Ferrous [Iron (II)] Fe²⁺	5. Chromium Cr³⁺
6. Lithium Li⁺	6. Magnesium Mg²⁺	6. Ferric [Iron (III)] Fe³⁺
7. Sodium Na⁺	7. Manganese Mn²⁺
8. Potassium K⁺	8. Mercuric [Mercury (II)] Hg²⁺	Tetravalent electropositive
9. Mercurous [Mercury (I)] Hg⁺	9. Nickel Ni²⁺	1. Plumbic [Lead (IV)] Pb⁴⁺
	10. Plumbous [Lead (II)] Pb²⁺	2. Platinic [Platinum (IV)] Pt⁴⁺
	11. Platinous [Platinum (II)] Pt²⁺	3. Stannic [Tin (IV)] Sn⁴⁺
	12. Stannous [Tin (II)] Sn²⁺
	13. Zinc Zn²⁺

Table shhowing List of some common electrovalent negative ions (acid radicals)

Monovalent electronegative	Divalent electronegative	Trivalent electronegative
1. Acetate CH₃COO⁻	1. Carbonate CO₃²⁻	1. Arsenate AsO₄³⁻
2. Bicarbonate/Hydrogen carbonate HCO₃⁻	2. Dichromate Cr₂O₇²⁻	2. Nitride N³⁻
3. Bisulphide/Hydrogen sulphide HS⁻	3. Oxide O²⁻	3. Aluminate AlO₃³⁻
4. Bisulphate/Hydrogen sulphate HSO₄⁻	4. Peroxide O₂²⁻	4. Arsenite AsO₃³⁻
5. Bisulphite/Hydrogen sulphite HSO₃⁻	5. Sulphate SO₄²⁻	5. Phosphide P³⁻
6. Bromide Br⁻	6. Sulphite SO₃²⁻	6. Phosphite PO₃³⁻
7. Chloride Cl⁻	7. Sulphide S²⁻	7. Phosphate PO₄³⁻
8. Permanganate MnO₄⁻	8. Silicate SiO₃²⁻	8. Borate BO₃³⁻
9. Fluoride F⁻	9. Thiosulphate S₂O₃²⁻
10. Hydride H⁻	10. Zincate ZnO₂²⁻	Tetravalent electronegative
11. Hydroxide OH⁻	11. Plumbite PbO₂²⁻	1. Carbide C⁴⁻
12. Iodide I⁻	12. Stannate SnO₃²⁻	2. Ferrocyanide Fe(CN)₆⁴⁻
13. Cyanide CN⁻	13. Manganate MnO₄²⁻
14. Nitrate NO₃⁻	14. Chromate CrO₄²⁻
15. Nitrite NO₂⁻	15. Oxalate (COO)₂²⁻
16. Chlorite ClO₂⁻
17. Hypochlorite ClO⁻
18. Chlorate ClO₃⁻
19. Perchlorate ClO₄⁻
20. Meta-aluminate AlO₂⁻

Writing Chemical Formulae – Clear & Concise Guide

1. The Criss-Cross Method Explained

Identify the Ions
Write the positive ion (cation) first, then the negative ion (anion)
Example: For aluminum oxide → Al³⁺ and O²⁻
Note Their Valencies
Write the valency numbers as superscripts (ignore + or – signs)
Example: Al³ and O²
Cross the Numbers
Swap the valency numbers to become subscripts
Example: Al³O² becomes Al₂O₃
Simplify if Possible
Reduce subscripts to lowest whole numbers
Example: Ca²O² simplifies to CaO

2. Practical Examples

Compound	Ions	Valencies	Criss-Cross	Final Formula
Magnesium Chloride	Mg²⁺, Cl⁻	Mg², Cl¹	Mg₁Cl₂	MgCl₂
Aluminum Sulfate	Al³⁺, SO₄²⁻	Al³, SO₄²	Al₂(SO₄)₃	Al₂(SO₄)₃
Calcium Phosphate	Ca²⁺, PO₄³⁻	Ca², PO₄³	Ca₃(PO₄)₂	Ca₃(PO₄)₂

3. Essential Chemical Formulae

Compound Name	Formula	Containing Ions
Sodium Chloride	NaCl	Na⁺, Cl⁻
Potassium Nitrate	KNO₃	K⁺, NO₃⁻
Ammonium Carbonate	(NH₄)₂CO₃	NH₄⁺, CO₃²⁻
Iron(III) Oxide	Fe₂O₃	Fe³⁺, O²⁻

4. Naming Compounds – 5 Key Rules

Metal + Non-Metal Compounds
Name: Metal name + non-metal root + “-ide”
Example: CaCl₂ = Calcium chloride
Compounds with Two Non-Metals
Use prefixes (mono-, di-, tri-) to show atom counts
Example: N₂O₅ = Dinitrogen pentoxide
Oxygen-Containing Compounds
Name changes based on oxygen atoms:
Hypo- (least O), -ite (some O), -ate (more O), per- (most O)
Example: NaClO = Sodium hypochlorite
Acid Naming
Binary acids: “Hydro-” + non-metal + “-ic acid” (HCl = Hydrochloric acid)
Oxyacids: Non-metal + “-ous” or “-ic” + “acid” (H₂SO₄ = Sulfuric acid)
Common Names
Some compounds have special names:
H₂O = Water
NH₃ = Ammonia
CH₄ = Methane

Practice Quiz
What’s the formula when Ca²⁺ combines with NO₃⁻?
a) CaNO₃
b) Ca(NO₃)₂ ✓ (Correct! Needs two NO₃⁻ to balance Ca²⁺)
How would you name P₂O₅?
a) Phosphorus oxide
b) Diphosphorus pentoxide ✓ (Right! Uses prefixes)
Which is the correct name for H₂SO₃?
a) Sulfuric acid
b) Sulfurous acid ✓ (Correct! -ite becomes -ous in acids)
What’s wrong with “AlO” as a formula?
a) Needs simplification
b) Charges aren’t balanced ✓ (Al³⁺ needs O²⁻ in 2:3 ratio)
Chemistry Humor
Why did the chemist refuse to write KO?
It looked too explosive!
What did the sodium say to the chloride?
“Our bond is unbreakable!”
Why was the chemical equation sad?
It couldn’t balance its life!
What’s a chemist’s favorite dance?
The ionic shuffle!

Chemical Equations – Simplified Guide

1. Writing Chemical Equations (4 Steps)

List Reactants & Products
Reactants (left) and products (right) separated by an arrow (→)
Example: C + O₂ → CO₂
Use Correct Symbols/Formulae
Write elements/molecules in their standard forms
Example: H₂ (not H) for hydrogen gas
Add State Symbols (Optional)
(s)=solid, (l)=liquid, (g)=gas, (aq)=aqueous
Example: 2H₂(g) + O₂(g) → 2H₂O(l)
Balance the Equation
Ensure equal atoms on both sides (law of conservation of mass)

2. Example Equations

Word to Chemical:
“Hydrogen reacts with oxygen to form water”
2H₂ + O₂ → 2H₂O
Combustion Reaction:
CH₄ + 2O₂ → CO₂ + 2H₂O

3. Types of Chemical Reactions

Type	Example	Equation
1 reactant → 2+ products	Decomposition	2H₂O → 2H₂ + O₂
2 reactants → 1 product	Combination	N₂ + 3H₂ → 2NH₃
2 reactants → 2 products	Displacement	Zn + H₂SO₄ → ZnSO₄ + H₂
2 reactants → 3+ products	Complex	Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O

4. Skeleton vs Balanced Equations

Skeleton (Unbalanced): KNO₃ → KNO₂ + O₂ (O atoms unequal)
Balanced: 2KNO₃ → 2KNO₂ + O₂ (All atoms equal)

5. Why Balance Equations?

Law of Conservation of Mass: Matter cannot be created/destroyed. Total mass of reactants = total mass of products.
Example: 2H₂ + O₂ → 2H₂O (4g H₂ + 32g O₂ → 36g H₂O)

6. Balancing Methods

A. Hit & Trial Method

Count Atoms: List atoms on both sides
Balance One Element at a Time (start with least frequent)
Example:
Cu + HNO₃ → Cu(NO₃)₂ + NO₂ + H₂O (Unbalanced)
Steps:
1. Balance Cu: Already 1 on both sides
2. Balance N: 1→3 → Multiply HNO₃ by 4
3. Final: Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O

B. Partial Equation Method

Break Complex Reactions into simpler steps
Balance Each Step, then combine
Example (Iodine Liberation):
Step 1: H₂O₂ → H₂O + [O]
Step 2: 2KI + H₂O + [O] → 2KOH + I₂
Combined: 2KI + H₂O₂ → 2KOH + I₂

Key Takeaways

Always write correct formulae before balancing
Balance by adjusting coefficients (never change subscripts)
For complex reactions, partial equations simplify the process

Memory Tip: “Balance Like a Pro – Start with Metals, Save O & H for Last!”

Chemical Formula Writing Examples

Name of Compound	Symbols with valencies	Exchange of valency	Formula
Magnesium chloride	Mg²⁺ Cl⁻¹	Mg² Cl₁	MgCl₂
Calcium oxide	Ca²⁺ O²⁻ [Dividing by H.C.F. it becomes Ca¹⁺ O¹⁻]	Ca² O₂ → Ca¹ O¹	CaO
Aluminium hydroxide	Al³⁺ (OH)⁻¹	Al³ (OH)₁	Al(OH)₃
Phosphorus trioxide	P³⁺ O²⁻	P² O₃	P₂O₃
Sodium meta-aluminate	Na⁺ AlO₂⁻	Na¹ AlO₂¹	NaAlO₂
Sodium aluminate	Na⁺ AlO₃³⁻	Na₃ AlO₃¹	Na₃AlO₃

Table with some Important Chemical Formulae (Part 1)

Chemical Name	Symbol with charge	Formula	Chemical Name	Symbol with charge	Formula
Potassium chloride	K¹⁺Cl¹⁻	KCl	Potassium plumbite	K¹⁺PbO₂²⁻	K₂PbO₂
Potassium bromide	K¹⁺Br¹⁻	KBr	Sodium chloride	Na¹⁺Cl¹⁻	NaCl
Potassium iodide	K¹⁺I¹⁻	KI	Sodium hydroxide	Na¹⁺OH¹⁻	NaOH
Potassium hydroxide	K¹⁺OH¹⁻	KOH	Sodium nitrite	Na¹⁺NO₂¹⁻	NaNO₂
Potassium nitrite	K¹⁺NO₂¹⁻	KNO₂	Sodium nitrate	Na¹⁺NO₃¹⁻	NaNO₃
Potassium nitrate	K¹⁺NO₃¹⁻	KNO₃	Sodium hydrogen carbonate	Na¹⁺HCO₃¹⁻	NaHCO₃
Potassium hydrogen carbonate	K¹⁺HCO₃¹⁻	KHCO₃	Sodium hydrogen sulphite	Na¹⁺HSO₄¹⁻	NaHSO₃
Potassium hydrogen sulphite	K¹⁺HSO₃¹⁻	KHSO₃	Sodium hydrogen sulphate	Na¹⁺HSO₄¹⁻	NaHSO₄
Potassium hydrogen sulphate	K¹⁺HSO₄¹⁻	KHSO₄	Sodium metaluminate	Na¹⁺AlO₂¹⁻	NaAlO₂
Potassium metaluminate	K¹⁺AlO₂¹⁻	KAlO₂	Sodium sulphate	Na¹⁺SO₄²⁻	Na₂SO₃
Potassium permanganate	K¹⁺MnO₄¹⁻	KMnO₄	Sodium carbonate	Na¹⁺SO₄²⁻	Na₂SO₄
Potassium sulphite	K¹⁺SO₃²⁻	K₂SO₃	Sodium zincate	Na¹⁺ZnO₂²⁻	Na₂ZnO₂
Potassium sulphate	K¹⁺SO₄²⁻	K₂SO₄	Sodium plumbite	Na¹⁺PbO₂²⁻	Na₂PbO₂
Potassium carbonate	K¹⁺CO₃²⁻	K₂CO₃	Silver chloride	Ag¹⁺Cl¹⁻	AgCl
Potassium dichromate	K¹⁺Cr₂O₇²⁻	K₂Cr₂O₇	Ammonium chloride	NH₄¹⁺Cl¹⁻	NH₄Cl
Potassium zincate	K¹⁺ZnO₂²⁻	K₂ZnO₂	Ammonium sulphate	NH₄¹⁺SO₄²⁻	(NH₄)₂SO₄
			Ammonium hydroxide	NH₄¹⁺OH¹⁻	NH₄OH

Table with some Important Chemical Formulae (Part 2 – Calcium Compounds)

Chemical Name	Symbol with charge	Formula
Calcium chloride	Ca²⁺Cl¹⁻	CaCl₂
Calcium hydroxide	Ca²⁺OH¹⁻	Ca(OH)₂
Calcium nitrate	Ca²⁺NO₃¹⁻	Ca(NO₃)₂
Calcium hydrogen carbonate	Ca²⁺HCO₃¹⁻	Ca(HCO₃)₂
Calcium hydrogen sulphite	Ca²⁺HSO₃¹⁻	Ca(HSO₃)₂
Calcium sulphite	Ca²⁺SO₃²⁻	CaSO₃
Calcium sulphate	Ca²⁺SO₄²⁻	CaSO₄
Calcium carbonate	Ca²⁺CO₃²⁻	CaCO₃
Calcium oxide	Ca²⁺O²⁻	CaO
Calcium silicate	Ca²⁺SiO₃²⁻	CaSiO₃
Calcium nitride	Ca²⁺N³⁻	Ca₃N₂

Table of some Important Chemical Formulae (Part 3 – Magnesium and Zinc Compounds)

Chemical Name	Symbol with charge	Formula
Magnesium chloride	Mg²⁺Cl¹⁻	MgCl₂
Magnesium hydroxide	Mg²⁺OH¹⁻	Mg(OH)₂
Magnesium nitrate	Mg²⁺NO₃¹⁻	Mg(NO₃)₂
Magnesium oxide	Mg²⁺O²⁻	MgO
Magnesium nitride	Mg²⁺N³⁻	Mg₃N₂
Zinc chloride	Zn²⁺Cl¹⁻	ZnCl₂
Zinc hydroxide	Zn²⁺OH¹⁻	Zn(OH)₂
Zinc nitrate	Zn²⁺NO₃¹⁻	Zn(NO₃)₂
Zinc sulphate	Zn²⁺SO₄²⁻	ZnSO₄
Zinc carbonate	Zn²⁺CO₃²⁻	ZnCO₃
Zinc oxide	Zn²⁺O²⁻	ZnO
Lead [II] chloride	Pb²⁺Cl¹⁻	PbCl₂
Lead [II] bromide	Pb²⁺Br¹⁻	PbBr₂
Lead [II] hydroxide	Pb²⁺OH¹⁻	Pb(OH)₂
Lead [II] nitrate	Pb²⁺NO₃¹⁻	Pb(NO₃)₂

Table of some Important Chemical Formulae (Part 4 – Other Metal Compounds)

Chemical Name	Symbol with charge	Formula
Lead [II] sulphate	Pb²⁺SO₄²⁻	PbSO₄
Lead [II] oxide	Pb²⁺O²⁻	PbO
Manganese chloride	Mn²⁺Cl¹⁻	MnCl₂
Manganese sulphate	Mn²⁺SO₄²⁻	MnSO₄
Aluminium chloride	Al³⁺Cl¹⁻	AlCl₃
Aluminium sulphate	Al³⁺SO₄²⁻	Al₂(SO₄)₃
Aluminium hydroxide	Al³⁺OH¹⁻	Al(OH)₃
Aluminium sulphide	Al³⁺S²⁻	Al₂S₃
Aluminium oxide	Al³⁺O²⁻	Al₂O₃
Chromium chloride	Cr³⁺Cl¹⁻	CrCl₃
Chromium sulphate	Cr³⁺SO₄²⁻	Cr₂(SO₄)₃
Chromium oxide	Cr³⁺O²⁻	Cr₂O₃
Copper [I] (cuprous)	Cu¹⁺Cl¹⁻	CuCl
Copper [I] chloride	Cu¹⁺O²⁻	Cu₂O
Copper [I] oxide	Cu¹⁺S²⁻	Cu₂S
Copper [I] sulphide	Cu²⁺Cl¹⁻	CuCl₂
Copper [II] (cupric)	Cu²⁺OH¹⁻	Cu(OH)₂
Copper [II] chloride	Cu²⁺NO₃¹⁻	Cu(NO₃)₂
Copper [II] hydroxide	Cu²⁺SO₄²⁻	CuSO₄
Copper [II] nitrate	Cu²⁺S²⁻	CuS
Copper [II] sulphate	Cu²⁺O²⁻	CuO
Copper [II] sulphide	Cu²⁺O²⁻	CuO
Copper [II] oxide	Cu²⁺SO₄²⁻	CuSO₄

Table with some Important Chemical Formulae (Part 5 – Iron Compounds)

Chemical Name	Symbol with charge	Formula
Iron [II] (ferrous)
Iron [II] chloride	Fe²⁺Cl¹⁻	FeCl₂
Iron [II] hydroxide	Fe²⁺OH¹⁻	Fe(OH)₂
Iron [II] nitrate	Fe²⁺NO₃¹⁻	Fe(NO₃)₂
Iron [II] sulphate	Fe²⁺SO₄²⁻	FeSO₄
Iron [II] sulphide	Fe²⁺S²⁻	FeS
Iron [II] oxide	Fe²⁺O²⁻	FeO
Iron [III] (ferric)
Iron [III] chloride	Fe³⁺Cl¹⁻	FeCl₃
Iron [III] sulphate	Fe³⁺SO₄²⁻	Fe₂(SO₄)₃
Iron [III] hydroxide	Fe³⁺OH¹⁻	Fe(OH)₃
Iron [III] sulphide	Fe³⁺S²⁻	Fe₂S₃
Iron [III] nitrate	Fe³⁺NO₃¹⁻	Fe(NO₃)₃
Iron [III] oxide	Fe³⁺O²⁻	Fe₂O₃

Naming Certain Compounds (Chemical Nomenclature) and Valency Calculation – Summary

1. Naming Chemical Compounds (5 Rules)

(1) Metal + Non-Metal Compounds
Format: Metal name + Non-metal root + “-ide”
Example:
Calcium + Nitrogen → Calcium nitride (Ca₃N₂)

(2) Two Non-Metals
Use prefixes (mono-, di-, tri-) to indicate atom counts.
Example:
PCl₃ → Phosphorus trichloride
PCl₅ → Phosphorus pentachloride

(3) Compounds with Oxygen
Naming depends on oxygen count:
Hypo-…-ite: Least oxygen (e.g., NaClO → Sodium hypochlorite)
…-ite: 2 oxygen (e.g., NaClO₂ → Sodium chlorite)
…-ate: 3 oxygen (e.g., NaClO₃ → Sodium chlorate)
Per-…-ate: Most oxygen (e.g., NaClO₄ → Sodium perchlorate)

(4) Naming Acids
Binary Acids (H + Non-metal):
“Hydro-” + Non-metal root + “-ic acid”
Example: HCl → Hydrochloric acid
Oxyacids (H + Polyatomic ion):
“-ate” ion → “-ic acid” (H₂SO₄ → Sulfuric acid)
“-ite” ion → “-ous acid” (H₂SO₃ → Sulfurous acid)

(5) Common (Trivial) Names
NH₃ → Ammonia (not “Nitrogen trihydride”)
H₂O → Water (not “Dihydrogen oxide”)

2. Calculating Valency from Formulas

Steps:

Write the formula (e.g., NO₂).
Swap subscripts/superscripts:
NO₂ → N²O¹
Multiply by known valencies (O = 2):
N²O¹ → N⁴O²
Result: Valency of N = 4.

Example Table:

Step	Action	Example (NO₂)
1	Write formula	NO₂
2	Swap subscripts	N²O¹
3	Multiply by O’s valency (2)	N⁴O²
4	Determine valency	N = 4

Key Points:

Uses standard valencies: H=1, O=2, Cl=1.
Works for both elements and radicals.

Key Takeaways

Naming Rules: Depends on composition (metal/non-metal, oxygen content, acid type).
Valency Calculation: Swap subscripts, adjust using known valencies, and simplify.
Exceptions: Common names (e.g., water, ammonia) override systematic rules.

Exercise 1(A) Solutions

Question 1: What is a symbol? What information does it convey?

Answer:
A chemical symbol is a short representation of an element that conveys three key pieces of information:

The name of the element (e.g., ‘S’ stands for sulphur)
One atom of that element
The atomic mass of the element (e.g., ‘N’ represents 14 atomic mass units of nitrogen) (From Chapter 1.2 – Chemical Symbols section, page 2 of the textbook)

Question 2: Why is the symbol S for sulphur, but Na for sodium and Si for silicon?

Answer:
Chemical symbols follow these conventions:

Sulphur (‘S’): Derived from its English name
Sodium (‘Na’): From Latin “Natrium” to avoid confusion with sulphur
Silicon (‘Si’): From Latin “Silex” (flint) to distinguish it from other elements This system was established by Berzelius to create a standardized notation. (Refer to Table 1.1 and Chapter 1.2, page 2)

Question 3: If the symbol for cobalt, Co, were written as CO, what would be wrong with it?

Answer:
The capitalization makes a critical difference:

‘Co’ represents the element cobalt (a single metallic atom)
‘CO’ represents carbon monoxide (a compound molecule containing one carbon and one oxygen atom) This distinction prevents confusion between elements and compounds in chemical notation. (From Chapter 1.2 note about symbol capitalization)

Question 4: What do the following symbols stand for?

(a) H
Represents one atom of the element hydrogen (atomic number 1)

(b) H₂
Represents one molecule of hydrogen gas consisting of two covalently bonded hydrogen atoms

Question 5:

(a) Explain the terms ‘valency’ and ‘variable valency’
Valency refers to the combining capacity of an atom, determined by the number of electrons it can lose, gain or share to achieve stability. Variable valency occurs when certain elements (particularly transition metals like iron, copper) can exhibit different valencies in different compounds due to the availability of electrons from multiple shells. (From Chapter 1.4 – Valency section, pages 4-5)

(b) How are elements with variable valency named?
Elements showing variable valency use:

The suffix “-ous” for the lower valency state (e.g., Ferrous for Fe²⁺)
The suffix “-ic” for the higher valency state (e.g., Ferric for Fe³⁺) Modern nomenclature uses Roman numerals (e.g., Iron(II) oxide for FeO) (From Chapter 1.4 – Variable Valency section, page 5)

Question 6: Give the formula and valency of:

(a) Aluminate → AlO₂⁻ (Valency: 1) (b) Chromate → CrO₄²⁻ (Valency: 2) (c) Aluminium → Al³⁺ (Valency: 3) (d) Cupric → Cu²⁺ (Valency: 2) (From Tables 1.3 and 1.4, pages 5-6)

Question 7: What is a chemical formula? What is the rule for writing a formula correctly?

Answer:
A chemical formula is the symbolic representation of a molecule that shows:

The elements present
Their relative proportions Rules for writing:
The electropositive element is written first
The electronegative element follows
Valencies are balanced using the criss-cross method
Subscripts are reduced to simplest whole numbers (From Chapter 1.3 – Formula section, page 3)

Question 8: What do you understand by the following terms?

(a) Acid radical
A negatively charged ion (anion) derived from acids that can combine with positive ions to form salts. Examples include Cl⁻ (from HCl) and SO₄²⁻ (from H₂SO₄).

(b) Basic radical
A positively charged ion (cation) derived from bases that can combine with negative ions to form salts. Examples include Na⁺ (from NaOH) and NH₄⁺ (from NH₄OH). (From Chapter 1.5 – Radicals section, page 5)

Question 9: Match the following compounds with their formulae

Original Table:

Compound	Formula Code
(a) Boric acid	(i) NaOH
(b) Phosphoric acid	(ii) SiO₂
(c) Nitrous acid	(iii) Na₂CO₃
(d) Nitric acid	(iv) KOH
(e) Sulphurous acid	(v) CaCO₃
(f) Sulphuric acid	(vi) NaHCO₃
(g) Hydrochloric acid	(vii) H₂S
(h) Silica (sand)	(viii) H₂O
(i) Caustic soda (sodium hydroxide)	(ix) PH₃
(j) Caustic potash (potassium hydroxide)	(x) CH₄
(k) Washing soda (sodium carbonate)	(xi) NH₃
(l) Baking soda (sodium bicarbonate)	(xii) HCl
(m) Limestone (calcium carbonate)	(xiii) H₂SO₃
(n) Water	(xiv) HNO₃
(o) Hydrogen sulphide	(xv) HNO₂
(p) Ammonia	(xvi) H₃BO₃
(q) Phosphine	(xvii) H₃PO₄
(r) Methane	(xviii) H₂SO₄

Answer Table:

Compound	Correct Formula	Match Code
(a) Boric acid	H₃BO₃	(xvi)
(b) Phosphoric acid	H₃PO₄	(xvii)
(c) Nitrous acid	HNO₂	(xv)
(d) Nitric acid	HNO₃	(xiv)
(e) Sulphurous acid	H₂SO₃	(xiii)
(f) Sulphuric acid	H₂SO₄	(xviii)
(g) Hydrochloric acid	HCl	(xii)
(h) Silica (sand)	SiO₂	(ii)
(i) Caustic soda	NaOH	(i)
(j) Caustic potash	KOH	(iv)
(k) Washing soda	Na₂CO₃	(iii)
(l) Baking soda	NaHCO₃	(vi)
(m) Limestone	CaCO₃	(v)
(n) Water	H₂O	(viii)
(o) Hydrogen sulphide	H₂S	(vii)
(p) Ammonia	NH₃	(xi)
(q) Phosphine	PH₃	(ix)
(r) Methane	CH₄	(x)

(From common names reference in the textbook)

Question 10: Select the basic and acidic radicals in:

(a) MgSO₄ → Basic: Mg²⁺, Acidic: SO₄²⁻

(b) (NH₄)₂SO₄ → Basic: NH₄⁺, Acidic: SO₄²⁻

(d) ZnCO₃ → Basic: Zn²⁺, Acidic: CO₃²⁻

(e) Mg(OH)₂ → Basic: Mg²⁺, Acidic: OH⁻

(From Chapter 1.5 – Radicals section and Tables 1.3-1.4)

Question 11: Formula for A³⁺ + B²⁻?

Answer:
Using the criss-cross method:

Write symbols with valencies: A³⁺ B²⁻
Cross the valencies: A₂B₃ Example: Al³⁺ + O²⁻ → Al₂O₃ (aluminium oxide)

(From Chapter 1.6 – Writing Chemical Formulae, page 6)

Question 12: Write chemical formula of:

(a) Aluminium sulphate → Al₂(SO₄)₃
Explanation: Al³⁺ + SO₄²⁻ → Cross valencies (2×3=6) → Al₂(SO₄)₃

(b) Ammonium sulphate → (NH₄)₂SO₄
Explanation: NH₄⁺ + SO₄²⁻ → Cross valencies → (NH₄)₂SO₄

(c) Zinc sulphate → ZnSO₄
Explanation: Zn²⁺ + SO₄²⁻ → Simplify 2:2 ratio → ZnSO₄
(From Chapter 1.6 – Criss-cross method)

Question 13: Write chemical names of:

(a) Ca₃(PO₄)₂ → Calcium phosphate
Rule: Metal + polyatomic ion name

(b) K₂CO₃ → Potassium carbonate
Rule: “-ate” suffix for CO₃²⁻

(d) Mn₃(BO₃)₂ → Manganese borate
Rule: Metal + “-ate” for BO₃³⁻

(e) Mg(HCO₃)₂ → Magnesium bicarbonate
Rule: “Hydrogen carbonate” alternate name

(From Chapter 1.7 – Naming Compounds)

Question 14: Identify radicals and write formulae for:

(a) Barium sulphate

Basic radical: Ba²⁺
Acidic radical: SO₄²⁻
Formula: BaSO₄

(b) Bismuth nitrate

Basic radical: Bi³⁺
Acidic radical: NO₃⁻
Formula: Bi(NO₃)₃

(Process repeated for all sub-questions using Tables 1.3-1.4)

Question 15: Name these chlorine-oxygen compounds:

(a) NaClO → Sodium hypochlorite
Rule: “Hypo-” prefix for least oxygen

(b) NaClO₂ → Sodium chlorite
Rule: “-ite” suffix for intermediate oxygen

(d) NaClO₄ → Sodium perchlorate
Rule: “Per-” prefix for most oxygen
(From Chapter 1.7 – Oxygen compounds naming)

Question 16: Complete the statements:

(a) The formula represents:
(iii) a molecule
Explanation: Formulas show molecular composition (e.g., H₂O = one water molecule)

(b) Correct formula of aluminium oxide:
(iii) Al₂O₃
Explanation: Al³⁺ + O²⁻ → Criss-cross gives Al₂O₃

NO₂ → N²O¹
Multiply by O’s valency (2): N⁴O²
(From Valency calculation method in Chapter 1.8)

Key Takeaways

Symbols: Latin/English origins, capitalization matters (Co vs CO)
Valency: Determines compound formation (use criss-cross method)
Naming:
1. “-ide” for simple anions
1. “-ite”/”-ate” for oxyanions
1. Prefixes for non-metal compounds
Radicals: Cations (positive) and anions (negative) combine to form neutral C + O₂ → CO₂compounds

CHEMICAL EQUATION

A chemical equation is a symbolic representation of a chemical reaction using the symbols and formulae of the substances involved. For example, the burning of coal in air produces carbon dioxide, which can be represented as:

Word equation :
Carbon + Oxygen → Carbon dioxide
Chemical equation : \(C+O_2→CO_2\)

Steps for Writing a Chemical Equation:

Write the symbols or formulae of the reactants on the left, separated by a (+) sign.
Write the symbols or formulae of the products on the right, separated by a (+) sign.
Place an arrow between the reactants and products to show the direction of the reaction.
Represent reactants and products in their molecular forms (since atomic forms are usually unstable).

Example:
Sodium reacts with water to form sodium hydroxide and hydrogen: \(2Na+2H_2 O→2NaOH+H_2\)

A chemical equation clearly identifies the reactants (starting substances) and products (substances formed). For instance: \(CuSO_4 + 2NaOH \longrightarrow Cu(OH)_2+Na_2SO_4\)
Here, copper sulphate and sodium hydroxide (reactants) yield copper hydroxide and sodium sulphate (products).

Types of Chemical Reactions:

Chemical reactions can involve:

One reactant and two or more products:

Example: \(Example: CaCO_3\longrightarrow Cao + CO_2\) (thermal decomposition).

Two reactants and one product:

Example: \(N_2+3H_2\longrightarrow 2NH_3\) (synthesis of ammonia).

Two reactants and two products:

Example: \(AgNO_3 + NaCl\longrightarrow AgCl+NaNO_3\) (double displacement).

Two reactants and three or more products:

Table of Contents

Unlocking the Secrets of Chemical Communication

SYLLABUS

Chemical Symbols & Formulas – Easy Summary

Valency – Simplified Summary

Variable Valency – Simplified Summary

Radicals – Simplified Summary

Table showing List of some common electrovalent positive ions (basic radicals)

Table shhowing List of some common electrovalent negative ions (acid radicals)

Writing Chemical Formulae – Clear & Concise Guide

1. The Criss-Cross Method Explained

2. Practical Examples

3. Essential Chemical Formulae

4. Naming Compounds – 5 Key Rules

Chemical Equations – Simplified Guide

1. Writing Chemical Equations (4 Steps)

2. Example Equations

3. Types of Chemical Reactions

4. Skeleton vs Balanced Equations

5. Why Balance Equations?

6. Balancing Methods

Memory Tip: “Balance Like a Pro – Start with Metals, Save O & H for Last!”

Chemical Formula Writing Examples

Naming Certain Compounds (Chemical Nomenclature) and Valency Calculation – Summary

1. Naming Chemical Compounds (5 Rules)

2. Calculating Valency from Formulas

Key Takeaways

Exercise 1(A) Solutions

Key Takeaways

CHEMICAL EQUATION

Steps for Writing a Chemical Equation:

Types of Chemical Reactions: