An atom is the smallest particle of an element such as carbon, hydrogen or nitrogen that retains the properties of that element. Break an atom of carbon down any further, and it will no longer be carbon. Children have trouble conceptualizing things they cannot see, and they usually do not have the vocabulary to discuss ideas such as "elements" and "microscopic," so explaining the concept of the atom to a young child can be difficult. To do it, you can employ a number of physical props.
Show the graphite refill to your child and tell her that it is made of material called carbon, which is an element.
Demonstrate to your child how you can break the graphite into smaller and smaller pieces. Keep breaking the graphite until the pieces are truly miniscule, and explain to the child that the graphite could eventually be broken into pieces so small you could not see them without a microscope.
Tell the child that the smallest possible piece of an carbon that you could break the graphite into would be called an "atom," and that if you broke the atom apart, it would no longer be carbon.
Place the dinner plate in front of your child and tell her that you will show her what an atom would look like if she could see it through a super-powerful microscope.
Place the red beads in the center of the dinner plate. Explain that every atom has protons in its center and that a carbon atom, like the ones that make up graphite, has six protons.
Intermix the white beads with the red beads. Tell your child that these are neutrons.
Set the blue beads all around the perimeter of the plate. Explain to your child that these are electrons and that they orbit the protons and neutrons just like the planets orbit the sun. Tell her that most atoms have the same number of electrons as they do protons.
Remove a red bead from the center of the plate and tell your child that what makes the atoms of different elements different from each other is the number of protons in the middle. If you change the proton number, you change the element.