During chemical reactions, the atoms in the reactants rearrange to form products with different properties.

The idea of atoms rearranging in a chemical reaction can be an advanced concept for elementary school teachers. You can experience a physical representation of this abstract concept by modeling what happens in a chemical reaction. Use different colored clay shaped in small spheres to model the atoms, and use toothpicks to model the bonds connecting the atoms to each other.

Start with simple reactions such as the splitting of water to form hydrogen gas and oxygen gas (remember that hydrogen gas consists of two hydrogen atoms connected to each other, and oxygen gas has two oxygen atoms connected to each other). For this reaction, you will need to start with two molecules of water, which split to form two molecules of hydrogen and one molecule of oxygen. The connections among the atoms definitely rearrange to make this happen.

For an advanced exercise, you can practice this modeling for the reaction that happens when cells burn sugar to get energy (respiration). This complex reaction involves molecules mentioned in Standard 1g (water, sugar, oxygen, and carbon dioxide). It also deepens understanding of cellular respiration, which is one of the Life Science standards for this grade level (Standard 2g).

In respiration, one sugar molecule combines with six oxygen molecules to form six molecules of carbon dioxide and six molecules of water. You will need 18 oxygen atoms, 12 hydrogen atoms, and 6 carbon atoms. You will definitely need to rearrange how the atoms connect with each other.

The molecules of sugar, water, and carbon dioxide should look like:

carbon dioxide  O – C – O

water  H – O – H

The major feature of a sugar molecule is that five carbon atoms join with one oxygen atom to form a hexagon. The other carbon, oxygen and hydrogen atoms are connected as shown below.

Modeling the splitting of water and respiration of sugar reinforces that oxygen gas occurs as molecules of diatomic gas and not as isolated oxygen atoms (as discussed in the Overview for this set of standards).