Name: atoms and their subatomic particles
Uploaded: 2026-06-01T06:28:00.281Z
Duration: 1 min 33 s
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K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Space Systems

3.3.9-12.A

Atomic Structure

Elements are substances with unique physical and chemical properties that cannot be broken down into other substances by chemical reactions.Each element, like potassium, consists of atoms that differ from those of other elements.These differences are found in the subatomic particles that make up each atom.Two of these particle types are clustered in a central nucleus. Protons are positively charged, while neutrons are uncharged, neutral.While both contribute to the atomic mass, each carrying approximately one atomic mass unit, the number of protons, referred to as the atomic number, defines the specific element. Changing the number of protons results in a different element.Electrons, a third type of subatomic particle, are negatively charged and move rapidly in a cloud around the nucleus.This cloud is mostly empty space and makes up the vast majority of an atom&#x27;s volume.Electrons remain near the nucleus because they are attracted to the positive charge of protons.An atom contains an equal number of protons and electrons, which cancels out the positive and negative charges, leading to no net charge.But, depending on their valence electron configuration, some atoms tend to gain or lose electrons to reach a more stable electron arrangement. In this case, they can lose electrons and become positively charged ions called cations or gain electrons and become negatively charged ions called anions.

atomic structure

All matter is composed of atoms, the smallest individual units of elements. Each atom is made up of three subatomic particles: protons, neutrons, and electrons. Together, these three particles account for the mass and the charge of an atom.<h4>The History of Atomic Theory</h4>The first person to propose that everything on Earth is made up of tiny particles was the Greek philosopher Democritus, around 450 B.C. He used the term atomos, Greek for &#x201C;indivisible,&#x201D; from which the modern term &#x201C;atom&#x201D; is derived. His idea was not taken seriously at the time, however, and it was many centuries before the concept of the atom would be revived. In the 19th century, John Dalton proposed the atomic theory that is still largely correct today. He put forth five postulates to explain how atoms made up the world around us: (1) all matter is composed of infinitely small particles, or atoms; (2) all atoms of a given element are identical to one another and (3) are different from the atoms of all other elements; (4) two or more elements can combine in a fixed ratio to form a compound; and (5) atoms cannot be created or destroyed in a chemical reaction, but they can be rearranged to form new substances.<h4>Discovering the Subatomic Particles that Make up the Atom</h4>Dalton was only partially correct about the particles that make up matter. While atoms cannot be broken down further by ordinary chemical or physical processes, they are composed of three smaller subatomic particles. The first clue about the subatomic structure came at the end of the 19th century when J.J. Thomson discovered the electron. Scientists knew that the overall charge of an atom was neutral, but Thomson&#x2019;s &#x201C;plum pudding model&#x201D; of the atom attempted to reconcile this new information regarding the existence of a negatively-charged particle, suggesting that electrons were found studded throughout an area of positive charge. Just a few years later, Ernest Rutherford performed an experiment showing that most of an atom&#x2019;s mass is concentrated in the nucleus, where protons account for an atom&#x2019;s positive charge, and the tiny negatively-charged electrons make up most of the space outside of the nucleus. This disproved Thomson&#x2019;s plum pudding model and brought scientists one step closer to the familiar model of the atom we know today. The neutron was discovered later, in 1932, by James Chadwick. This final piece of the puzzle meant that scientists had now accounted for all the mass present in an atom with protons and neutrons, and all of its charge with protons and electrons.<h4>The Structure of an Atom</h4>Protons are found in the nucleus of an atom, have a positive charge, and a mass of one atomic mass unit (AMU) each. The number of protons is equal to the atomic number on the periodic table and determines the identity of the element. Neutrons are also found in the nucleus. They have no charge, but they have the same mass as protons and thus contribute to the atomic mass of an atom. Electrons orbit around the nucleus in clouds. They have a negative charge and negligible mass, so they contribute to the overall charge of an atom, but not to its mass.

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KEY TERMS AND CONCEPTS

Learn by watching this video about Atomic Structure: Protons, Neutrons and Electrons at JoVE.com

atoms and their subatomic particles

Atoms are the smallest units of elements, and they make up all matter. Each atom contains three subatomic particles: protons, neutrons, and electrons. These particles give an atom its mass and its charge.

The idea that matter is made of tiny particles goes back to Democritus, a Greek philosopher around 450 B.C. He used the word atomos, which means “indivisible.” The idea was not accepted at the time, but it returned many centuries later.

In the 19th century, John Dalton proposed an atomic theory that is still mostly correct today. He said that all matter is made of tiny atoms, that atoms of the same element are alike, and that atoms of different elements are different. He also said that elements combine in fixed ratios to form compounds, and that atoms are not created or destroyed in chemical reactions, but can be rearranged into new substances.

Dalton was only partly right about what atoms are made of. At the end of the 19th century, J.J. Thomson discovered the electron. Scientists already knew atoms had no overall charge, so Thomson suggested the plum pudding model. In this model, negatively charged electrons were spread through a region of positive charge.

A few years later, Ernest Rutherford showed that most of an atom’s mass is concentrated in the nucleus. The nucleus is the dense center of the atom. Rutherford’s work showed that protons give the atom its positive charge, while the tiny negative electrons occupy most of the space outside the nucleus. This result replaced Thomson’s plum pudding model.

The last major particle was found in 1932 by James Chadwick. He discovered the neutron. With protons and neutrons, scientists could account for the mass of the atom. With protons and electrons, they could account for its charge. Protons are found in the nucleus, have a positive charge, and each has a mass of one atomic mass unit, or AMU.

Atoms and Their Subatomic Particles

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Periodic Table Basics for Living Things

The periodic table helps explain which elements living things need and how those elements are related. Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all occur naturally, and even fewer are essential for life. Living matter is made mostly of carbon, nitrogen, hydrogen, and oxygen. Together, these elements make up most of the human body and are also found in all life on Earth. Smaller amounts of calcium,...

Atoms are the smallest units of elements, and they make up all matter. Each atom contains three subatomic particles: protons, neutrons, and electrons. These particles give an atom its mass and its charge. The idea that matter is made of tiny particles goes back to Democritus, a Greek philosopher around 450 B.C. He used the word atomos, which means “indivisible.” The idea was not accepted at the time, but it returned many centuries later. In the 19th century, John Dalton proposed an atomic...

isotopes

Atomic Mass and Isotope Basics

Atomic mass and isotopes are linked by the number of protons and neutrons in an atom. The number of protons sets an element’s atomic number, or Z. For example, every atom with eight protons is oxygen. Atoms of the same element can still differ because they can have different numbers of neutrons. The mass number, or A, is the total of protons and neutrons. Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have several isotopes. Carbon-12, carbon-13,...

electron behavior

Electron Shells and Valence Electrons

Electrons are negatively charged subatomic particles that occupy regions around the positively charged nucleus of an atom. Their location is linked to energy levels called shells. They are also grouped into sub-shells and orbitals within each shell. An electron’s shell shows its general energy level. Electrons closer to the nucleus have less energy, while electrons farther away have more energy. The sub-shell gives a more exact location and energy level. An orbital is the shape of the region...

electron orbital model

Electron Orbitals and Energy Levels

Electron orbitals show where electrons are most likely to be found around the atomic nucleus. They also help explain energy levels, orbital shapes, and three-dimensional orientation. In an atom, electron location is described first by a shell, or principal energy level. It is then described by a subshell within that shell and by the individual orbitals inside each subshell. The first shell is closest to the nucleus. It has only one subshell and one spherical orbital, called the 1s orbital.

covalent bonds

Electronegativity and Covalent Bond Polarity

Covalent bonds form when two atoms share electrons to fill their valence shells. The way those shared electrons are pulled depends on electronegativity, which is an atom’s ability to attract electrons in a bond. When atoms have similar electronegativities, they form nonpolar covalent bonds. When their electronegativities differ, the bond is polar because the electrons are shared unevenly. The number of covalent bonds an atom can make depends on its valence electrons. Oxygen has six valence...

ionic bonds

Ionic Compounds and Electrolytes

Ionic compounds form when atoms gain or lose electrons to reach a more stable electron configuration. The charged particles that result are called ions. Ionic bonds are electrostatic attractions between oppositely charged ions. The most reactive elements include those with one valence electron, such as potassium, and those that need one more valence electron, such as chlorine. Ions that lose electrons become positive cations. Ions that gain electrons become negative anions. Cations and anions...

hydrogen bonds

Hydrogen Bonds in Water

Hydrogen bonds in water are weak attractions between atoms that are already part of other chemical bonds. One atom is electronegative, such as oxygen, and carries a partial negative charge. The other is a hydrogen atom that is bonded to another electronegative atom and has a partial positive charge. These attractions form because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom like oxygen or nitrogen. The electrons in that bond are shared unequally.

van der waals interactions

Intermolecular Forces in Polar Solutions

Intermolecular forces are the attractions and repulsions that act between atoms and molecules. These electrostatic forces come from particles with permanent, partial, or temporary charges. For neutral atoms and molecules, the main types are ion-dipole, dipole-dipole, and dispersion forces, which are together called van der Waals forces. Polar molecules have a partial positive end and a partial negative end. That separation of charge creates a dipole. In water, oxygen is more electronegative...

elements and compounds

Elements, Compounds, and Bonding

Elements and compounds are the two main kinds of pure substances. A pure substance contains only one kind of matter. An element contains only one type of atom. A compound contains two or more types of atoms joined by a chemical bond. Elements can be atomic or molecular, depending on their basic units. They are unique forms of matter with specific chemical and physical properties. Ordinary chemical reactions cannot break an element into a smaller substance. There are 118 elements, but only 98...

molecular shapes

Electron Geometry and Lone Pairs

Electron geometry and lone pairs help explain why molecules take specific shapes. The arrangement of electron groups around a central atom controls the molecular geometry. Valence electrons form bonding pairs, which sit mainly between bonded atoms, or lone pairs, which belong to one atom only. Electron pairs in the valence shell spread out to reduce repulsion. They do this by maximizing the distance between one another. A diatomic molecule has two regions of electron density, and these are...

pH Scale in Everyday Solutions

pH measures how acidic or basic a water-based solution is. It depends on the concentration of hydronium ions, H3O+, in the solution. In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. Because hydronium ion levels can vary over a very wide range, measuring pH directly in moles is not practical. The pH scale converts hydronium ion concentration into a negative logarithm. Pure water has a pH of 7 and is neutral. Most solutions fall between 0 and 14, but some, such...

chemical reactions

Atoms, Bonds, and Chemical Reactions

Chemical reactions rearrange atoms to form new substances. In a reaction, the starting materials are called reactants, and the new substances are called products. The atoms stay the same type and number, but their bonds change, so the substances become different compounds. During a chemical reaction, bonds between atoms break and form again. This means the shared electrons are rearranged. Some reactions happen on their own, while others need an energy source such as heat or light. In biology,...

redox reactions

Electron Transfer in Redox

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together. The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing...

cohesion

Water Molecules and Surface Tension

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature. Cohesion helps water form droplets on a surface. Water does not...

adhesion

Water Climbing by Adhesion

Water can climb or stick to surfaces because of adhesion, which is the attraction between different kinds of molecules. In water, this is easy to see on polar surfaces such as glass or cellulose in plants. The positive hydrogen side of water is more attracted to the negative oxygen in silica than to nearby water molecules. This attraction helps explain capillary action. If a narrow glass tube is placed in a beaker of water, water molecules attach to the tube’s surface and the water level rises.

states of water

Water Phase Changes and Ice Density

Water changes between solid, liquid, and gas states as temperature and molecular motion change. In this lesson, the focus is on how water freezes, melts, vaporizes, and returns to liquid or solid form. The balance between intermolecular forces, which pull molecules together, and kinetic energy, which pushes them apart, controls each state. Water freezes when intermolecular forces become stronger than kinetic energy. Unlike most substances, ice is less dense than liquid water. This happens...

specific heat

How Specific Heat Affects Temperature

Specific heat capacity describes how much energy a substance needs to rise by 1 degree Celsius for each gram. It is often written with calories, grams, and degrees Celsius, but it can also be shown in joules, kilograms, and Kelvin. For water, 1 gram needs 1 calorie to increase by 1°C, which is also written as 1 cal/g-°C or 4186 J/kg/K. Water has a high specific heat capacity, so it takes in a large amount of heat before its temperature changes much. It also gives off a lot of heat when it...

vaporization

Vaporization, Boiling, and Evaporation

Vaporization changes a liquid into vapor when temperature adds enough kinetic energy to overcome intermolecular forces. It is a surface phenomenon, which means it starts at the liquid’s surface. The energy needed to vaporize a set amount of liquid at a given pressure and constant temperature is called the heat of vaporization. Water shows this process clearly. When liquid water is vaporized, it becomes steam. One way this happens is boiling, which occurs when vapor bubbles form beneath the...

solvents

Water as a Biological Solvent

Water acts as a biological solvent in many living systems. A solvent is a substance, usually a liquid, that dissolves another substance called a solute. When a solvent and a solute mix, they form a solution, which is a uniform mixture of both parts. Water is called a universal biological solvent because its polar structure helps it dissolve many other polar compounds. Polarity means that one side of the molecule has a slight positive charge and the other side has a slight negative charge.

carbon skeletons

Carbon Backbones in Biomolecules

Carbon backbones give biological molecules their structure and flexibility. Living things are built from macromolecules that contain carbon atoms, and organic compounds are defined by a carbon backbone. Carbon is tetravalent, so each carbon atom can bond with four other atoms. Its valence electrons are stable, so carbon rarely becomes an ion. As carbon chains get longer, they can form ring structures, double bonds, and branching side chains. Carbon-carbon bonds create the carbon skeleton.

key terms and concepts

Learn how protons, neutrons, and electrons shape atomic mass and charge, and trace the history of atomic theory from Democritus to Chadwick.

Atoms and Their Subatomic Particles | JoVE K12

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Physical Science

Structure and Properties of Matter

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Matter and Its Interactions

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Earth's Place in the Universe

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the-principle-of-superposition-and-the-gravitational-field

The Principle of Superposition and the Gravitational Field

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Students who demonstrate understanding can develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun's core to release energy in the form of radiation.  Clarification Statement: Emphasis is on the energy transfer mechanisms that allow energy from nuclear fusion in the sun's core to reach Earth.  Examples of evidence for the model include observations of the masses and lifetimes of other stars, as well as the ways that the sun's radiation varies due to sudden solar flares ("space weather"), the 11-year sunspot cycle, and non-cyclic variations over centuries.  Assessment Boundary: Assessment does not include details of the atomic and sub-atomic processes involved with the sun's nuclear fusion.

Emission Spectra

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Atomic Spectroscopy: Absorption, Emission, and Fluorescence

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Space-Time Curvature and the General Theory of Relativity

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The Wave Nature of Light

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Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Metal Flame Emission

Metal Flame Emission
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Molecular Spectroscopy: Absorption and Emission

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Atomic Emission Spectroscopy: Instrumentation

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Atomic Absorption Spectroscopy: Radiation and Light Sources

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Students who demonstrate understanding can construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.  Clarification Statement: Emphasis is on the astronomical evidence of the red shift of light from galaxies as an indication that the universe is currently expanding, the cosmic microwave background as the remnant radiation from the Big Bang, and the observed composition of ordinary matter of the universe, primarily found in stars and interstellar gases (from the spectra of electromagnetic radiation from stars), which matches that predicted by the Big Bang theory (3/4 hydrogen and 1/4 helium).  Assessment Boundary:

3.3.9-12.B

Spectrophotometry: Introduction

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Ultraviolet and Visible (UV&ndash;Vis) Spectroscopy: Overview

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Students who demonstrate understanding can communicate scientific ideas about the way stars, over their life cycle, produce elements.  Clarification Statement: Emphasis is on the way nucleosynthesis, and therefore the different elements created, varies as a function of the mass of a star and the stage of its lifetime.  Assessment Boundary: Details of the many different nucleosynthesis pathways for stars of differing masses are not assessed.

3.3.9-12.C

Tidal Forces

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Students who demonstrate understanding can use mathematical or computational representations to predict the motion of orbiting objects in the solar system.  Clarification Statement: Emphasis is on Newtonian gravitational laws governing orbital motions, which apply to human-made satellites as well as planets and moons.  Assessment Boundary: Mathematical representations for the gravitational attraction of bodies and Kepler's Laws of orbital motions should not deal with more than two bodies, nor involve calculus.

3.3.9-12.D

Atoms and Their Subatomic Particles

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