All About Atoms

Lesson Plan - Get It!

Audio:

Through the previous three Related Lessons in our Atoms series, found in the right-hand sidebar, you have learned about the structure of the atom by studying subatomic particles.

You learned that the atom is made up of protons and neutrons in the dense nucleus, surrounded by a cloud of moving electrons. Atoms make up the entire world (there's your answer!), from a grain of sand to an elephant!

The subatomic particles found in atoms determine the type of substance. Remember that protons are positively charged, and are used to identify the atom.

For example, all atoms of calcium will have 20 protons, because that is the atomic number. The number of protons will not change, because it is unique to that element.

• Can you remember how to calculate the number of neutrons in calcium?

Take the atomic mass, 40, and subtract the atomic number, 20. That means that an atom of calcium has 20 neutrons. However, not all atoms of calcium really have 20 neutrons. The number of neutrons can fluctuate!

When an atom has more or less neutrons than it is supposed to, it is called an isotope. Isotopes exist naturally throughout our world.

• Have you ever heard of carbon-12, carbon-13, and carbon-14?

The numbers represent the atomic masses. These different atomic forms have different numbers of neutrons, and that impacts the overall atomic mass.

• Notice how each atom of carbon has a different number of neutrons?

That causes the entire atom to have different atomic mass than is shown in the periodic table. Remember that all elements are listed on the periodic table. Isotopes can cause an atom to become radioactive, which means it is able to give off energy through radioactive decay.

The number of electrons in an atom can fluctuate as well! In a neutral atom, the number of protons equals the number of electrons. This balances the positive and negative charges. The atom of sodium shown below has 11 protons and 11 electrons; therefore, it is neutral:

Take a moment to watch Atomic Structure (1 of 6) What Are Atoms? An Explanation from Step-by-Step Science to review what you've learned so far:

Remember that electrons are the bonding tool in an atom, with shells sharing or giving up electrons. When the number of electrons changes, it creates a special atom called an ion.

Ions are charged atoms, and can have a positive or negative charge.

Study the image above carefully, and note how the number of electrons changed. When an atom has more electrons than protons, it has a negative charge. We call these ions anions.

When an atom has fewer electrons than protons, it carries a positive charge. These ions are called kations or cations. When an atom becomes an ion, it is more likely to bond with another atom to regain stability. A neutral atom is a stable atom!

The structure of the atom determines the elemental identity. All atoms on the planet earth represent an element found on the periodic table. They are classified based on the number of protons, because the number of neutrons and electrons can fluctuate.

Isotopes occur because of variations in the number of neutrons in an atom, whereas ions form when an atom gains or loses electrons. These atoms have special features that power our world and allow us to enjoy ice cream! Without atoms, our world would look very different! In fact, it's safe to say, without atoms, there would be no world!

• Why do you think it is important to understand the role of atoms in our world?

Write a quick reflection about this on a sheet of paper before moving on.

In the Got It? section, you will complete a lab on isotopes and atomic mass.