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Chemical Symbols and Formulas

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Chemical Symbols and Formulas

Use element symbols and formula rules to decode the materials labels. Remember: the first letter of a symbol is uppercase, any second letter is lowercase, and a subscript tells how many atoms of the element immediately before it are present. No subscript means one atom.

Read the labels

Each question is a clue from the materials checklist.

1.The checklist says the sensor casing contains iron. Which symbol should be written on the label?

2.Is the symbol Mg written with correct capitalisation for magnesium? Explain the capitalisation rule briefly.

3.Match each element with its symbol: hydrogen, sodium, chlorine, carbon and oxygen.

Hydrogen
Sodium
Chlorine
Carbon
Oxygen

4.One draft label reads co for cobalt. Rewrite the symbol correctly, then state why the draft is wrong.

Decode the formulas

Count each element’s atoms in one formula unit or molecule. A subscript applies only to the element immediately before it.

5.A water label reads H₂O. How many hydrogen atoms and oxygen atoms does one water molecule contain?

6.A sealed sample is labelled CO₂. Select the correct atom count.

1 carbon and 2 oxygen atoms
2 carbon and 1 oxygen atom
1 carbon and 1 oxygen atom
2 carbon and 2 oxygen atoms

7.Complete the atom counts for calcium chloride, CaCl₂: calcium atoms = ; chlorine atoms = .

8.A cleaning fluid is labelled CH₄. Name the elements and give the total number of atoms in one molecule.

Repair and build labels

Use the element symbols and the stated atom counts to make clear, correctly written formulas.

9.A label printer produces h2o. Rewrite this formula using correct chemical-symbol capitalisation and subscript notation.

10.Select every correctly written formula for a compound.

Nacl
CO₂
CaCl₂
ch4
NH₃

11.Write the formula for each stated atom combination: (a) one carbon and two oxygen atoms; (b) one sodium and one chlorine atom; (c) one nitrogen and three hydrogen atoms.

12.Describe how to show the atoms in H₂O, and explain how the formula tells you what to include.

13.A sample is labelled Fe₂O₃. How many iron atoms and oxygen atoms does the formula represent? What does the small 3 tell you?