Atom

Atoms are the tiny building blocks that make up everything around us. They are the smallest pieces of matter that still keep the properties of an element.

What Atoms Are Made Of

An atom has a center called a nucleus. The nucleus contains protons and neutrons. Around the nucleus, there are tiny particles called electrons that move in a cloud.

Size and Weight

Atoms are very, very small. They are much smaller than we can see with our eyes or even with a regular microscope. Most of an atom’s mass is in its nucleus.

How Atoms Form New Things

Atoms can stick together to form new substances. This is how we get things like molecules and crystals. When atoms join or separate, it causes many of the changes we see in nature. This is what the science of chemistry studies.

History of atomic theory

Main article: History of atomic theory

The word atom comes from an ancient Greek word meaning "uncuttable." Long ago, people believed that everything was made of tiny particles that could not be broken down. This was just an idea, not science.

In the early 1800s, a scientist named John Dalton proved that matter is made of small units called atoms.

Dalton studied how elements combine. He learned that when elements form new substances, they do so in simple ratios. For example, there are different kinds of tin oxide. One kind has one atom of oxygen for each atom of tin, while another has two atoms of oxygen for each atom of tin. This showed that atoms are the building blocks of matter.

Later, scientists found that atoms could be broken down. In 1897, J. J. Thomson discovered a tiny particle called the electron, which is much smaller than an atom. Then, Ernest Rutherford found that atoms have a small, dense center called a nucleus, with electrons moving around it. This changed how we understand atoms.

Structure

Main article: Subatomic particle

Atoms are made of tiny parts called subatomic particles. The three main parts are electrons, protons, and neutrons.

Electrons are very small and have a negative charge. They move around the center of the atom. Protons are bigger than electrons and have a positive charge. They are in the center with neutrons, which have no charge but are heavy like protons. The number of protons tells us what element the atom is.

The center of the atom, called the nucleus, is where the protons and neutrons are found. It is much smaller than the whole atom. The number of protons and neutrons can change, but this needs a lot of energy. When atoms join or split, they can release big amounts of energy. This is why the Sun shines and why nuclear power works.

See also: Electronegativity

The electrons in an atom are found in areas around the center called electron shells. These shells are where we often find the electrons. The electrons can move between shells by gaining or losing energy. When they do this, they give off or take in light. This is why each element has its own pattern of colors when heated. How the electrons are arranged helps atoms bond together to make molecules and different materials.

Properties

Atoms are the tiny building blocks that make up everything around us. Each atom has a central part called the nucleus, made of protons and neutrons, surrounded by electrons. The number of protons decides what element the atom is — for example, all hydrogen atoms have one proton.

Atoms can have different versions called isotopes. These have the same number of protons but different numbers of neutrons. Some isotopes are stable and stay the same, while others are radioactive and change over time. Atoms are very small — a human hair is about a million carbon atoms wide! Atoms can join together to form molecules and different materials like solids, liquids, and gases.

Identification

Atoms are so tiny that we can't see them with normal tools. But special devices like the scanning tunneling microscope can show us atoms on surfaces. This microscope uses an amazing effect called quantum tunneling. This effect lets tiny particles pass through barriers they normally couldn't.

We can also tell atoms apart by their weight. When an atom loses a tiny part called an electron, it becomes charged. We can then bend its path with a magnetic field. The way it bends tells us the atom's weight. Tools like the mass spectrometer help scientists measure these weights. This helps scientists figure out what atoms are present.

Origin and current state

Baryonic matter makes up a small part of the energy in the universe. It has very few particles. Inside galaxies like the Milky Way, there are more particles, especially in areas called the interstellar medium. Stars form from these clouds and make new elements.

Most matter in the Milky Way is inside stars. It is too hot there for atoms to stay together. Atoms became common about 380,000 years after the Big Bang when the universe cooled down. Elements heavier than iron are made in big events, like when stars explode or crash into each other. On Earth, most atoms have been here since the planet formed. Some were made later by natural processes or by people.