Protons, Neutrons, and Electrons — Reading Comprehension

Atoms are the basic units of matter, and everything we see around us is made up of them. At the center of each atom is a dense nucleus, which contains two types of subatomic particles: protons and neutrons. Outside the nucleus, much farther away, are tiny, rapidly moving electrons. Understanding how these three particles interact is essential to explaining the structure and behavior of all matter.

Subatomic Particles and Their Roles

Protons are positively charged particles located in the nucleus of every atom. The number of protons in an atom determines which element it is. For example, every hydrogen atom has one proton, while every carbon atom has six. Neutrons are also found in the nucleus, but they have no electric charge—they are neutral. Neutrons add mass to the atom and help stabilize the nucleus. Electrons are negatively charged and are found in regions called energy levels or shells around the nucleus. Although electrons have much less mass than protons or neutrons, their arrangement determines the atom’s chemical behavior. The interactions between electrons of different atoms allow for the formation of molecules and chemical reactions.

How Do We Know About Subatomic Particles?

Scientists used experiments and technology, such as the gold foil experiment and particle accelerators, to discover and study subatomic particles. For example, the discovery of the proton was made when Ernest Rutherford observed that some particles bounced back when fired at gold atoms. Later, the neutron’s existence was confirmed by James Chadwick. Modern technology allows scientists to measure the mass and charge of each particle. Protons and neutrons each have a mass of about 1 atomic mass unit (amu), while electrons are about 1/1,836 the mass of a proton. The chart below summarizes their properties:

Relative Mass and Charge of Subatomic Particles

Interactions and Applications

The number of protons defines the atomic number and identity of an element. Neutrons influence the atom’s mass and can create isotopes, which are atoms of the same element with different numbers of neutrons. Electrons, especially those in the outermost shell, determine how atoms bond and react with each other. For instance, sodium (with one electron in its outer shell) readily reacts with chlorine (which needs one electron) to form table salt. These interactions explain why chemical reactions happen and allow us to develop new materials, medicines, and technologies.

On a larger scale, understanding subatomic particles helps explain natural phenomena, such as why certain elements are radioactive or how stars produce energy. The principles of atomic structure connect to larger scientific ideas, including the conservation of matter and the periodic table’s organization.

Interesting Fact: All the atoms in your body—including their protons, neutrons, and electrons—were formed billions of years ago in the cores of stars!

What is found at the center of every atom?

Which subatomic particle determines the identity of an element?

Where are electrons located in an atom?

What is the relative mass of a neutron?

In the passage, what does 'chemical behavior' mean?

What is an isotope?

Why do electrons play a key role in chemical reactions?

True or False: Protons and neutrons have about the same mass.

True or False: Electrons are much heavier than protons.

If an atom has 8 protons, what element is it?