Cations

	Coloured				White				None
	NaOH (aq)	NH3 (aq)			NaOH (aq)	NH3(aq)			NaOH (aq)	NH3(aq)
Cu2+	I	*S		Zn2+	S	S		Ca2+	*I	-
Fe2+	I	I		Al3+	S	I		NH4+	-	-
Fe3+	I	I		Pb2+	S	I

 

 

Anions

	Coloured				White				None
	Reagent	Pdt			Reagent	Pdt			Reagent	Pdt
I-	H+ / Pb(NO3)2	PbI2		Cl-	H+ / AgNO3	AgCl		NO3-	Al/ NaOH Heat	NH3
				SO42-	H+ / Ba(NO3)2	BaSO4		CO32-	H+	CO2
I		Pee	on	Ch  SO		Ag      Ba	with	NO   CO		NH3 CO

(A) Naming of ionic compounds [ 'Metal' + 'Non-metal' ]

Pre-requisites

A1) Write on top of the Roman numerals of the Periodic Table 1+ 2+ 3+ ..... as shown below.

	1+	2+		3+	4+/4-	3-	2-	1-	0
	I	II		III	IV	V	VI	VII	0

 

A2) Highlight the elements as shown below. Call this 'a 7 and a dot'. These standalone elements will always be       

        written as X₂. They are diatomic.

	I	II		III	IV	V	VI	VII	0
			H
						N	O	F
								Cl
								Br
								I
								At

 

A3) Memorise these commonly used polyatomic ions.   

	NH4+	NO3-	OH-	HCO3-	CO32-	SO42-	SO32-	PO43-
	ammonium	nitrate	hydroxide	hydrogencarbonate	carbonate	sulfate	sulfite	phosphate

 

A4) For metal ions with Roman Numerals, they are either transition metals or Group IV metals, the charge of the

       metal ion follows the Roman Numerals assigned.  

(i)   iron (II) ...       means charge of iron is 2+.         It is written as Fe²⁺.

(ii)  iron (III) ...     means charge of iron is 3+.         It is written as Fe³⁺.

(iii) copper (I) ...    means charge of copper is 1+.    It is written as Cu⁺.

(iv) copper (II) ...  means charge of copper is 2+.    It is written as Cu²⁺.

(v)  lead (II) ....     means charge of lead is 2+.        It is written as  Pb²⁺.

(vi) lead (IV) ....     means charge of lead is 4+.        It is written as  Pb⁴⁺.

 

 

Q1 : Chemical formula of calcium chloride. 

A1 : Step 1 : Now, look at the Periodic Table and refer to A1. Write down Ca²⁺ and Cl^-.

        Step 2 : Cross 'number only NOT CHARGES' to bottom of the element. Hence, Ca is 1 and Cl is 2 like this. Ca₁Cl₂

        Step 3 : There is no need to put 1 for Ca as it is understood as '1' NOT '0'. Therefore, final answer : CaCl₂

 

Q2 : Chemical formula of sodium chloride. 

A2 : Step 1 : Now, look at the Periodic Table and refer to A1. Write down Na⁺ and Cl^-.

        Step 2 : If the numerically charges are the same (e.g 1+  1- or 2+  2- or 3+  3- , ignore crossing and simply write as, in   

                      this case, NaCl.)

 

Q3 : Chemical formula of calcium hydroxide. 

A3 : Step 1 : Now, look at the Periodic Table and refer to A1, write down Ca²⁺. Refer to A3, write down OH^-.

        Step 2 : Cross 'number only NOT CHARGES' to bottom of the ions. Hence, Ca is 1 and OH is 2 like this Ca₁OH₂

         Step 3 : Since OH- is polyatomic ion, bracket (OH). Ignore '1' for Ca to get the final answer Ca(OH)₂.

 

Q4 : Chemical formula of iron (III) sulfate. 

A4 : Step 1 : Refer to A4, write down Fe³⁺. Refer to A3, write down SO₄^2-.

        Step 2 : Cross 'number only NOT CHARGES' to bottom of the ions. Hence, Fe is 2 and SO₄ is 3 like this Fe₂SO_{4 3}

         Step 3 : Since SO₄^2- is polyatomic ion, bracket (SO₄) to get the final answer Fe₂(SO₄)₃.

 

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(B) Naming of covalent compounds  [ Non-metal + Non-metal ]

 Pre-requisites

B1) Memorise the prefixes of the following.

	1	2	3	4	5	6	7	8	9	10
	mono-	di- or bi-	tri-	tetra-	penta-	hexa-	hepta-	octa	nona-	deca-

 

 

Q1 : Chemical formula of carbon dioxide.

A1 : Step 1 : Now, look at the Periodic Table and look for the symbol of carbon. Write down C.

        Step 2 : Oxide comes from the element oxygen. Now look for symbol oxygen. Write down O.

        Step 3 : Refer to B1. 'di' means 2. Therefore, final answer is CO₂. Note : O comes first, then 2.

 

Q2 : Chemical formula of sulfur trioxide.

A2 : Step 1 : Now, look at the Periodic Table and look for the symbol of sulfur. Write down S.

        Step 2 : Oxide comes from the element oxygen. Now look for symbol oxygen. Write down O.

        Step 3 : Refer to B1. 'tri' means 3. Therefore, final answer is SO₃. Note : O comes first, then 3.

 

Q3 : Chemical formula of dinitrogen tetroxide.

A4 : Step 1 : Now, look at the Periodic Table and look for the symbol of nitrogen. Write down N.

        Step 2 : Oxide comes from the element oxygen. Now look for symbol oxygen. Write down O.

        Step 3 : Refer to B1. 'di' means 2 and 'tetra' means 4. Therefore, final answer is N₂O₄. 

        Note : N comes first, then 2. O comes first, then 4.

       

       Suppose you follow the writing of the chemical formula, the name should be sulfur oxide-tri or carbon oxide-di. As this naming

       sounds awkward, the naming convention follows that the prefix precedes the element.

 

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(C) Naming of acids and bases

Pre-requisites

C1)  Mineral acids have a 'H' in front while inorganic bases have an 'O' or 'OH' behind.

C2)  Aqueous ammonia is the only base without 'O' or 'OH' behind in the chemical formula and it is written as       

        NH₃ (aq).

        (Note : Ammonium hydroxide does not exist.)

C3)  Organic acids have a '-COOH' behind while organic bases have a '-NH₂' behind.

C4)  Prefixes of organic compounds. 

No. of carbon atoms	1	2	3	4	5	6	7	8
Prefix	meth-	eth-	prop-	but-	pent-	hex-	hept-	oct-
Structural Prefix	CH3	C2H5	C3H7	C4H9	C5H11	C6H13	C7H15	C8H17

 

 

 

Q1 : Chemical formula of sulfuric acid. 

A1 : Step 1 : Refer to C1, write down H⁺. Refer to A3, write down SO₄^2- as sulfuric comes from sulfate.

                     Note : All '-ric' comes from '-ate' & '-rous' comes from '-ite'.

        Step 2 : Cross 'number only NOT CHARGES' to bottom of the ions. Hence, H is 2 and SO₄ is 1 like this H₂SO_{4 1}

         Step 3 : SO₄^2- is polyatomic ion, bracket (SO₄)₁ but this is redundant as (SO₄)₁ is understood as SO₄.

                      Final answer : H₂SO₄.

 

Q2 : Chemical formula of ethanoic acid. 

A2 : Step 1 : Refer to C3, write down COOH as it is an organic acid, -oic acid. Refer to C4, write CH₃ NOT C₂H₅ as the     

                      C in COOH contributes to 1 carbon. Naming is based on the number of carbon atoms present in compound.

        Step 2 : Combine them and you get CH₃COOH.

 

Q3: Chemical formula of iron (III) hydroxide. 

A4 : Step 1 : Refer to A4, write down Fe³⁺. Refer to A3, write down OH^-.

        Step 2 : Cross 'number only NOT CHARGES' to bottom of the ions. Hence, Fe is 1 and OH is 3 like this Fe₁ OH ₃

         Step 3 : Since OH^- is polyatomic ion, bracket (OH) and ignore '1' to get the final answer Fe(OH)₃.

 

Q4 : Chemical formula of methylamine. 

A4 : Step 1 : Refer to C3, write down NH₂ as it is an organic base, -amine. Refer to C4, write CH₃ as it is a methyl. 

        Step 2 : Combine them and you get CH₃NH₂.

 

General rule of the thumb : Non-metal + Non-metal --> Covalent

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STEP 1

Identify the Group the non-metals belong to.

For example in H₂O, O atom belongs to Group VI (2- hence 2 lines) while

                                   H atom is unplaced but has 1 lone electron (1- hence 1 line).

 

STEP 2

Identify the Period the non-metals belong to and overlap the outermost electron shells.

O atom belongs to Period 2 hence draw 2 concentric circles while

H atom belongs to Period 1 hence draw 1 circle

(Ensure that the outermost circles overlap to house the shared electrons as shown below.)

Single bond = 1 pair of shared electrons.      'x•'  

Double bond = 2 pairs of shared electrons.   'x•x•'

Triple bond = 3 pairs of shared electrons.     'x•x•x•'

 

 

STEP 3

Fill in the Remaining Unbonded electrons for the elements and include the Legend.

In this case for O, 4 'x' electrons for outermost shell and 2 'x' electrons in the first shell.

Count the total number of outermost electrons of each atom. O atom is 8 while H atom is 2. 

The stable noble gas electronic configuration of the outermost electrons is either 8 or 2.