Counting Atoms

Front

What is an element in chemistry?

Back

An element is a pure substance that cannot be broken down into simpler substances by chemical means. Each element is made up of atoms that have the same number of protons.

Front

How do you determine the number of elements in a chemical formula?

Back

Count the different capital letters in the formula. Each capital letter represents a different element.

Front

What does the subscript in a chemical formula indicate?

Back

The subscript indicates the number of atoms of the element that are present in the molecule. For example, in H₂O, the '2' indicates there are 2 hydrogen atoms.

Front

What is a coefficient in a chemical formula?

Back

A coefficient is a number placed in front of a chemical formula to indicate how many molecules or moles of that substance are present. For example, in 3H₂O, the '3' indicates there are 3 water molecules.

Front

How many hydrogen atoms are in the formula 3(NH₄)₂CrO₄?

Back

There are 24 hydrogen atoms.

Front

How do you calculate the total number of atoms in a compound?

Back

Multiply the number of atoms of each element by its subscript and then sum all the products.

Front

What is the formula for calculating the number of oxygen atoms in Al₂(SO₄)₃?

Back

In Al₂(SO₄)₃, there are 3 sulfate ions, each containing 4 oxygen atoms, so the total is 3 x 4 = 12 oxygen atoms.

Front

How many magnesium atoms are in 10MgCl₂?

Back

There are 10 magnesium atoms.

Front

What does the formula NaCl represent?

Back

NaCl represents sodium chloride, which is composed of one sodium atom and one chlorine atom.

Front

How many sodium atoms are in 6NaCl?

Back

There are 6 sodium atoms.