Basic chemistry help for students and teachers


Interactive Chemistry Worksheets for Students


Periodic table

Naming compounds

Basic formula

Simple compounds

Ionic compounds 1

Ionic compounds 2

Chemical suffixes

Old chemical names

Hydrocarbons - Alkanes

Alkanes, alkenes & alkynes

Alkanols to alkanoic acids


Common compounds

Common formula quiz

Acids, bases and salts

Covalent compounds

Printable worksheets



This chemical formula writing worksheet contains over 200 compounds to solve involving binary and polyatomic ions. Answers are included. More printable formula worksheets are included below.


Teaching students how to write chemical formula

Here is my accumulated knowledge and methodology.  I have been teaching Chemistry for over 20 years and have tried all sorts of ways to teach students how to write chemical formula.

The following method and learning sequence is a quick and easy way to teach students from Junior High School or Middle School (Steps 1-4) through to Senior High School (Steps 1-8). 

Ions, charges and superscripts are not introduced in the early stages as they confuse less able students. Common student errors are also noted in some of the worksheets to help student making mistakes.


1. How to name a compound from its elements

i)   When a metal element chemically combines with a non-metal element a compound is formed.

ii)  The compound is given a name. The metal is named first and the non-metal is named second.

iii) The suffix of the non-metal is changed to an "ide" to indicate that a compound has been formed.

Metal + Non-metal Ionic Compound

Sodium + Chlorine Sodium Chloride

Elements and Compounds Worksheet. US Spelling.

Elements and Compounds Worksheet. International Spelling.


2.  How to determine the combining power of an element

The combining power of an element is also called its valency.

Students can use the Periodic Table to find the combining power of many elements. This is an important step in teaching students how to write the chemical formula of a number of simple of ionic compounds.

Valencies and the Periodic table - US

Valencies and the Periodic table - International


3.  How to use valencies to write chemical formula

The 'arms and link' method is a quick and easy way for students to learn how to write the chemical formula of compounds. 

Using this method the chemical formula of aluminum chloride (US spelling) or aluminium chloride (International Spelling) can easily be determined as shown by the illustration below.

Al has a combining power of 3.It has 3 arms. Cl has a combining power of 1. It has 1 arm. To link all the arms of Al three Cl's must be used. The chemical formula for this compound is therefore AlCl3.

Note: Subscripts are used when an element in a compound appears more than once.

In the above example a small 3 is written in the formula, AlCl3  to show that Cl appears 3 times. to 



4. Binary Ionic Compounds Worksheet

The worksheet contains over 100 chemical formulas for students to solve. Compounds containing two elements only are used which are between a metal and a non-metal. ie. Binary ionic compounds.

For the transition metals students need to learn that the combining power of zinc is always 2 and silver is always 1. Romans numerals are used to indicate the combining power of lead, tin and the transitions metals.

Chemical formula - Simple binary compounds - US

Chemical formula - Simple binary compounds - International


5. Common Acids, Bases and Polyatomic Ions

The following chemical model helps students to learn the relationship between the chemical formula of the common acids and bases with the ions they produce in a chemical reaction.

A polyatomic ion is a charged chemical species which consists of two or more different elements. eg. The phosphate ion, PO43- consists of two different elements, phosphorus and oxygen and carries a negative charge of 3.


Acids, Bases and Ions - Formula models

Chemical Bingo is a great way to drill students and help them to learn the chemical formula of a range of common acids, bases and polyatomic ions.

Acids, Bases and Polyatomic Ions - Chemical Bingo Sheet

You call also make your own game of chemical bingo.


6. Compounds with Polyatomic ions

Students have difficulty in writing the chemical formula of compounds with polyatomic ions. The following model helps students to visualize both the combining power and the chemical formula of a range of polyatomic ions.

Chemical species also combine with each other in whole number ratios. This is used in the writing of chemical formula.

a) Chemical formula model

Chemical formula models - US

Chemical formula models - International


b) Chemical formula worksheets - Compounds with polyatomic ions

The relationship between the charge of an ion and its combining power is continued to be shown to help students understand why chemicals combine with one another.

Chemical formula - Compounds containing basic polyatomic ions - US

Chemical formula - Compounds containing basic polyatomic ions -  International

The arms and link method can be continued to be shown to help students determine the chemical formula of a compound.

Note: Brackets are used a polyatomic group occurs more than once in a compound. In the above example, the sulfate or SO42- group occurs three times, so brackets are used. 


7. Drill - Writing the Chemical formula of a range of ionic compounds

Practice makes perfect. This worksheet contains 100 ionic compounds with solutions.

The distinction between the "ide" and "ate" suffix of chemical compounds is also reinforced as students are often confused between the two. While the following pairs of chemical names are similar in appearance their chemical formulas are different and need to be distinguished: sodium nitride & sodium nitrate; sodium sulfide & sodium sulfate and sodium phosphide & sodium phosphate. 

Chemical formula drill - US

Chemical formula drill - International


8. How to name Covalent Compounds

Non-metallic elements can combine with one another to produce covalent compounds.

Non-metal + Non-metal Covalent compound

The same non-metallic elements however, can produce a variety of covalent compounds under different reaction conditions.

For example nitrogen and oxygen can combine with one another to produce NO, N2O5, N2O, N2O4, N2O3 and NO2

Valencies cannot be used to determine the chemical formula of many of these compounds.

Students studying Senior Chemistry courses are however, expected to name covalent compounds.

How are they named?

How are covalent compounds named?


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