How many hands does an atom have?

The idea

The combining capacity of an element is the number of hydrogen or chlorine atoms with which one of its atoms combines to form a compound, as hydrogen and chlorine each have a combining capacity of one.

Two hydrogens for one oxygen

In water, H₂O, one atom of oxygen is joined to two atoms of hydrogen.

What number would you give as the combining capacity of oxygen from this?

• 2
• 1
• 3

Count the partner atoms

Open each tab and count the hydrogen or chlorine atoms joined to one central atom.

Counting partners

We measure the combining capacity with hydrogen or chlorine, because each of them has a combining capacity of one. The capacity is the number of such atoms that one atom joins.

The combining capacity of an element is the number of hydrogen or chlorine atoms with which one of its atoms combines to form a compound. Hydrogen and chlorine each have a combining capacity of one.

Notes

Combining capacity is the number of hydrogen or chlorine atoms one atom combines with. Hydrogen and chlorine each have combining capacity one.

Check yourself

In H₂O, one oxygen atom combines with 2 hydrogen atoms. What is the combining capacity of oxygen?

Answer: 2

It is the number of hydrogen atoms that combine with one oxygen atom: 2.

In NH₃, one nitrogen atom combines with 3 hydrogen atoms. What is the combining capacity of nitrogen?

Answer: 3

Three hydrogen atoms combine with one nitrogen atom, so its combining capacity is 3.

In MgCl₂, one magnesium atom combines with 2 chlorine atoms. What is the combining capacity of magnesium?

Answer: 2

Two chlorine atoms combine with one magnesium atom, so its combining capacity is 2.

The combining capacity of an element is counted in terms of atoms of …

• oxygen or nitrogen. Hydrogen and chlorine are used because each has a combining capacity of one.
• hydrogen or chlorine — correct. Yes!
• neutrons or electrons. The count is of hydrogen or chlorine atoms that one atom combines with.