What Is the Matter Made Of? A Simple Guide to Atoms and Molecules
Everything around you, the air you breathe, the screen you are reading this on, your own body, is made from tiny building blocks called atoms. Atoms are the basic units of matter, and they combine to form molecules. So the direct answer to what matter is made of is atoms and the particles inside them: protons, neutrons, and electrons. These particles themselves are made from even smaller things called quarks and leptons, but for most everyday purposes, atoms and molecules explain everything from a rock to a glass of water.
Atoms: The Basic Building Blocks
An atom is the smallest unit of a chemical element that still keeps the properties of that element. If you split an atom of gold, you no longer have gold.
Atoms have a central nucleus, which is dense and positively charged. The nucleus contains two types of particles:
- Protons — positively charged. The number of protons determines what element an atom is. Any atom with 6 protons is carbon, and any atom with 8 protons is oxygen.
- Neutrons — neutral (no charge). They add mass and help hold the nucleus together.
Around the nucleus, a cloud of electrons orbits. Electrons are negatively charged and very light, about 1/1836 the mass of a proton. The number of electrons normally equals the number of protons, making the atom neutral overall.
The space between the nucleus and the electrons is mostly empty. If an atom were the size of a football stadium, the nucleus would be about the size of a pea on the center spot.
What Holds the Nucleus Together?
The positively charged protons in the nucleus are held together by the strong nuclear force. This force is one of the four fundamental forces of nature (along with gravity, electromagnetism, and the weak nuclear force). It acts only at very short distances, roughly the size of an atomic nucleus, and it is powerful enough to overcome the electromagnetic repulsion between protons.
Molecules: Atoms in Combination
Atoms bond together to form molecules. A molecule is a group of two or more atoms held together by chemical bonds. Molecules can be as simple as two atoms (oxygen gas, O₂) or as complex as thousands of atoms (proteins, DNA).
The way atoms bond depends on their electrons. The outermost electrons, called valence electrons, are the ones that interact. Atoms tend to bond in ways that give them a full outer shell of electrons, usually eight electrons, a rule called the octet rule.
Types of Chemical Bonds
There are two main types of bonds that hold molecules together:
- Covalent bonds — atoms share electrons. This happens between nonmetal atoms. In water (H₂O), each hydrogen atom shares an electron with the oxygen atom.
- Ionic bonds — one atom gives an electron to another. This happens between a metal and a nonmetal. In table salt (NaCl), sodium gives an electron to chlorine. The sodium becomes positively charged, the chlorine becomes negatively charged, and the opposite charges attract.
A Worked Example: Water
Water is a common molecule. A water molecule (H₂O) has one oxygen atom and two hydrogen atoms. The oxygen atom shares one electron with each hydrogen atom. Because oxygen pulls electrons more strongly than hydrogen does, the shared electrons spend more time near the oxygen. This gives the oxygen end of the molecule a slight negative charge and the hydrogen ends a slight positive charge. That is why water is a polar molecule, it has a positive side and a negative side.
Beyond Atoms: Subatomic Particles and Fundamental Particles
The electron is a fundamental particle, it cannot be split into anything smaller (as far as we know). But protons and neutrons are not fundamental. They are made of quarks.
Quarks come in six types: up, down, charm, strange, top, and bottom. A proton is made of two up quarks and one down quark. A neutron is made of one up quark and two down quarks. The strong nuclear force between quarks is carried by particles called gluons.
The table below summarizes the main particles in matter:
| Particle | Type | Location | Charge | Made of? |
|---|---|---|---|---|
| Electron | Fundamental | Around nucleus | Negative | Not made of smaller particles |
| Proton | Composite | Nucleus | Positive | 2 up quarks + 1 down quark |
| Neutron | Composite | Nucleus | Neutral | 1 up quark + 2 down quarks |
| Quark | Fundamental | Inside protons/neutrons | Fractional (+2/3 or -1/3) | Not made of smaller particles |
The Royal Society of Chemistry provides detailed resources on atomic structure and bonding. Research at CERN continues to explore the fundamental particles that make up matter.
How Atoms Are Arranged: Elements, Isotopes, and Ions
Not all atoms of the same element are identical. Isotopes are atoms of the same element that have different numbers of neutrons. Carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons. Ions are atoms that have gained or lost electrons, giving them a net electric charge. A sodium atom that loses one electron becomes a sodium ion (Na⁺). A chlorine atom that gains one electron becomes a chloride ion (Cl⁻).
The Periodic Table: A Map of Matter
The periodic table organizes all known elements by their atomic number (number of protons). Elements in the same column, called a group, have similar chemical properties because they have the same number of valence electrons. Group 1 elements (alkali metals) like sodium each have one valence electron. Group 18 elements (noble gases) like helium have full outer electron shells and rarely form chemical bonds.
Chemical Reactions: Atoms Rearranging
In a chemical reaction, atoms are neither created nor destroyed. They are rearranged into different molecules. This is the law of conservation of mass. When methane (CH₄) burns in oxygen (O₂), the atoms rearrange to form carbon dioxide (CO₂) and water (H₂O). The same number of carbon, hydrogen, and oxygen atoms exist before and after the reaction.
States of Matter: How Atoms and Molecules Behave
The same atoms and molecules can exist in different states depending on temperature and pressure. In a solid, atoms or molecules are held in a fixed arrangement and vibrate in place. In a liquid, they move past each other but remain close together. In a gas, they move freely and fill any container. Plasma is a fourth state of matter where electrons are stripped from atoms, creating a mix of free electrons and positive ions. Plasma is common in stars and lightning.
Key Takeaways
- All matter is made of atoms, which consist of a nucleus (protons and neutrons) and orbiting electrons.
- The number of protons in an atom determines what element it is.
- Atoms bond together to form molecules through covalent bonds (sharing electrons) or ionic bonds (transferring electrons).
- Protons and neutrons are made of quarks, while electrons are fundamental particles with no known smaller parts.
- The strong nuclear force holds the nucleus together, overcoming the electromagnetic repulsion between protons.
