Atom

Everything is made of tiny bits.

These bits are called atoms. They are too small to see. They are even smaller than light.

An atom has a tiny center. This center is very heavy. Small parts fly around the center. These parts have a tiny charge. The center and the parts pull on each other. This pull keeps the atom together. Atoms can join to make new things.

This is how our world is built.

Everything in our world is made of tiny building blocks. These are called atoms.

Atoms are so small that we cannot see them. A single human hair is as wide as a million carbon atoms.

An atom has a center called a nucleus. The nucleus contains protons and neutrons. Protons have a positive charge. Neutrons have no charge. Most of an atom's mass is in this center.

Tiny parts called electrons fly around the nucleus. Electrons have a negative charge. The positive nucleus and negative electrons pull on each other. This pull holds the atom together.

We can tell different elements apart by their protons. For example, an atom with 11 protons is sodium. An atom with 29 protons is copper. If atoms have the same protons but different neutrons, they are called isotopes.

Sometimes atoms join together. They use chemical bonds to stick to other atoms. This makes new things like molecules or crystals. These changes are what scientists study in chemistry.

Everything in our world is made of tiny building blocks called atoms.

Atoms are the fundamental parts of matter and chemical elements. They are extremely small, usually around 100 picometers across. To imagine this, a single human hair is about a million carbon atoms wide. Atoms are even smaller than the shortest wavelength of visible light. Because of this, humans cannot see them with normal microscopes. They are so small that we cannot use old physics rules to predict how they act.

An atom works by having a center called a nucleus. This nucleus contains protons and usually neutrons. Protons have a positive electric charge. Neutrons have no charge at all. More than 99.94% of an atom's mass is found in this tiny nucleus.

Surrounding the nucleus is a swarm of electrons. Electrons have a negative charge. The positive nucleus and the negative electrons pull on each other. This electromagnetic force is what binds the electrons to the center. If an atom has the same number of protons and electrons, it is neutral. If the numbers are different, it becomes a charged atom called an ion.

Scientists have worked for a long time to understand these parts. The word atom comes from an ancient Greek word, atomos, meaning "uncuttable." In the early 1800s, John Dalton found evidence for atoms. He noticed patterns in how elements combined in different amounts. He used these patterns to show that elements have unique weights. Later, in 1897, J. J. Thomson discovered the electron. He found that these tiny, negative particles were much lighter than hydrogen.

Other scientists helped find the nucleus and how electrons move. Between 1908 and 1913, Ernest Rutherford studied how particles bounced off metal foils. His experiments showed that the positive charge is not spread out. Instead, it is concentrated in a tiny center called the nucleus.

In 1913, Niels Bohr proposed a new way to look at electrons. He suggested they move in specific orbits around the nucleus. He said they could jump between these orbits by gaining or losing energy. This helped explain why atoms stay stable instead of crashing inward.

Atoms are the reason we see so many different things in nature. We can tell different elements apart by counting their protons. For example, an atom with 11 protons is sodium. An atom with 29 protons is copper. Atoms can also attach to each other using chemical bonds. This creates new things like molecules or crystals. These connections allow atoms to form the many materials we use every day. Chemistry is the science that studies how these atoms change and bond.

Atoms are the fundamental building blocks of all matter. They are the basic particles that make up the chemical elements. Atoms are incredibly small, typically measuring around 100 picometers across. To visualize this, imagine a single human hair. That hair is about one million carbon atoms wide. Atoms are even smaller than the shortest wavelength of visible light. Because of this, humans cannot see them using conventional microscopes. They are so small that classical physics cannot accurately predict their behavior. Instead, scientists must use quantum effects to understand how they act.

An atom consists of a central nucleus surrounded by a swarm of electrons. The nucleus contains protons and generally neutrons. Protons carry a positive electric charge. Neutrons have no charge. These two particles are held together by the nuclear force. This force is usually stronger than the electromagnetic force. This strength allows the nucleus to stay together despite the protons repelling each other. More than 99.94% of an atom's mass is concentrated in this tiny nucleus.

Electrons are the particles that surround the nucleus. They carry a negative electric charge. The electrons are held in place by the electromagnetic force. This force acts between the negative electrons and the positive protons. If an atom has an equal number of protons and electrons, it is electrically neutral. However, atoms can become charged. A charged atom is called an ion. If an atom has more electrons than protons, it is a negative ion, or anion. If it has more protons than electrons, it is a positive ion, or cation.

Different chemical elements are defined by their proton count. The number of protons determines the identity of the atom. For example, any atom with 11 protons is sodium. Any atom with 29 protons is copper. Atoms can also have different numbers of neutrons. These are called isotopes of the same element. Atoms can also attach to one another through chemical bonds. This process forms chemical compounds like molecules or crystals. The ability of atoms to attach and detach is responsible for most physical changes in nature. Chemistry is the science that studies these changes.

The idea of the atom has a long history. The word comes from the Greek word "atomos," meaning "uncuttable." Ancient Greeks used this term based on philosophical reasoning. Modern atomic theory, however, is based on scientific evidence. In the early 19th century, John Dalton provided this evidence. He discovered the law of multiple proportions. He noticed that elements combine in specific ratios of small whole numbers. For instance, he found that tin and oxygen combine in different ratios to form different powders. He concluded that these ratios existed because elements combine in multiples of basic units.

In 1897, J. J. Thomson discovered the electron. He used cathode rays to show that atoms contained tiny, negatively charged particles. He found these particles were 1,700 times lighter than hydrogen. Thomson originally called them "corpuscles." He proposed a model where positive charge was spread out like a sphere. This was known as the plum pudding model. However, this model could not explain all atomic properties. Between 1908 and 1913, Ernest Rutherford challenged this idea. He bombarded metal foils with alpha particles. He saw some particles deflect at angles greater than 90 degrees.

Rutherford's experiment proved that the positive charge is not diffuse. He proposed that the positive charge is concentrated in a tiny nucleus. This nucleus carries almost all the atom's mass. In 1913, Niels Bohr improved this model. He addressed why electrons do not spiral into the nucleus. He proposed that electrons move in specific, discrete orbits. Electrons can jump between these orbits by absorbing or radiating energy. This concept is known as quantization. While the Bohr model is now considered obsolete, it helped explain how elements emit light.

Understanding the atom connects to many different scientific fields. The way nuclei split is a form of nuclear decay. This happens when the electromagnetic repulsion becomes stronger than the nuclear force. This process can leave behind different elements. The study of how atoms bond is the foundation of chemistry. The study of how particles behave at this scale is the foundation of quantum mechanics. By studying the smallest parts of matter, we learn how the entire universe is constructed.