Parts of an Atom — Reading Comprehension

Grades

Standards

MS-PS1-1
RI.6.3
RI.7.1

About This Reader

This reading passage on Parts of an Atom provides middle school students with a structured and accessible explanation of atomic structure. Aligned with NGSS standard MS-PS1-1 (Develop models to describe the atomic composition of simple molecules and extended structures) and Common Core Reading Standards for Informational Text, the content uses clear headings and subheadings to organize key concepts. The passage first introduces what an atom is, then systematically explains the three main components: protons (positive particles in the nucleus that determine the element), neutrons (neutral particles in the nucleus that add stability), and electrons (negative particles orbiting in shells). Additional sections explain how these parts maintain balance in neutral atoms and how changes in electron numbers create ions. This resource falls within Science→Physical Science→Properties of Matter and uses straightforward language with concrete examples to help students visualize microscopic atomic structures that form the foundation of matter.

CONTENT PREVIEW

1. Protons

The center of an atom is called the nucleus. This dense core contains protons and neutrons packed tightly together. Protons have a positive electrical charge. The number of protons in an atom determines what element it is - hydrogen has 1 proton, oxygen has 8, and gold has 79.

2. Neutrons

Neutrons are also found in the nucleus alongside protons. Neutrons have no charge at all, making them neutral particles. They add mass to the atom and help keep the nucleus stable.

3. Electrons

Orbiting around the nucleus are electrons, which are tiny particles with a negative charge. They move extremely fast in regions called electron shells or energy levels. The first shell can hold up to 2 electrons, the second shell up to 8, and so on. Unlike the heavy nucleus, electrons are incredibly lightweight - about 1/1836 the mass of a proton!

Atomic Balance

In a neutral atom, the number of protons equals the number of electrons, so the positive and negative charges balance out. When atoms gain or lose electrons, they become charged particles called ions.

Though incredibly small (about 0.1 nanometers across), atoms make up everything you can see, touch, and even yourself!

Fun fact: If you could stack 1 trillion protons on top of each other, the pile would only be about the size of a grain of salt! Yet despite their tiny size, the repulsive force between two protons that are 1 meter apart is strong enough to lift a weight of 10 million tons.

What is an atom?

The largest unit of matterA type of moleculeThe smallest unit of matter that keeps the properties of an elementA particle found only in liquids

What are the three main parts of an atom?

Protons, electrons, and ionsProtons, neutrons, and electronsNucleus, electrons, and shellsNucleus, protons, and charges

Where are protons located in an atom?

In the electron shellsOrbiting the nucleusIn the nucleusBetween electron shells

What electrical charge do neutrons have?

Positive chargeNegative chargeNo chargeVariable charge

What determines which element an atom is?

The number of electronsThe number of protonsThe number of neutronsThe combined mass of all particles

Where do electrons move in an atom?

Inside the nucleusIn electron shells or energy levelsIn a straight line around the nucleusThey don't move at all