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Protons, Neutrons, and Electrons — Reading Comprehension

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This comprehensive middle school science passage explores the roles of protons, neutrons, and electrons, the three main subatomic particles that make up atoms. Aligned with NGSS standard MS-PS1-1, the resource explains how protons determine element identity, neutrons add mass, and electrons influence chemical behavior. The passage integrates real-world applications, a relative mass and charge comparison chart, and connects atomic structure to larger scientific principles. It includes a glossary, multiple-choice quiz, writing prompts, and graphic organizers to support diverse learners. Audio integration makes this resource accessible for all students. This resource is perfect for teaching atomic structure in grades 6-8 and supports inquiry-based science instruction.

CONTENT PREVIEW

atom-2 — Protons, Neutrons, and Electrons

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

Particle	Charge	Relative Mass	Location
Proton	+1	1 amu	Nucleus
Neutron	0	1 amu	Nucleus
Electron	-1	~0.0005 amu	Outside nucleus

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?

NucleusElectronMoleculeShell

Which subatomic particle determines the identity of an element?

ProtonNeutronElectronMolecule

Where are electrons located in an atom?

Inside the nucleusIn the outer energy levels or shellsBetween protons and neutronsIn the atomic core

What is the relative mass of a neutron?

1 amu0 amu0.0005 amu10 amu

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

How an atom interacts and reacts with other atomsThe color of an atomThe amount of protons in an atomWhere the nucleus is located

What is an isotope?

Atoms of the same element with different numbers of neutronsAtoms with extra electronsA type of moleculeA charged nucleus