Team Chemistry -
Created by: Team Chemistry -, Last Updated: May 22, 2024


Atoms are the basic building blocks of matter in chemistry. They are tiny particles that make up everything around us, including the air we breathe, the food we eat, and even our own bodies. Each atom consists of a nucleus, containing protons and neutrons, surrounded by electrons that orbit the nucleus. Atoms combine in various ways to form molecules and compounds, which are the substances we study in chemistry to understand the properties and behaviors of different materials.

What is a Atom?

An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus containing protons and neutrons, with electrons orbiting around the nucleus. Atoms are the building blocks of everything around us, from the air we breathe to the food we eat. They combine in various ways to form molecules and compounds, which make up all the substances we encounter in our daily lives.

Formula for Number of Atoms

To calculate the number of atoms in a sample, you use the formula:

Number of atoms = (mass of the sample / molar mass) × Avogadro’s number

First, divide the mass of your sample by the molar mass of the element or compound. Then, multiply the result by Avogadro’s number, which is 6.022×10²³. This formula helps you determine how many individual atoms are present in a given amount of substance.

Types of Atoms

Atoms come in different types based on the number of protons in their nucleus, which defines the element. Here are the main types:

  1. Hydrogen Atoms: These atoms have one proton and one electron. They are the simplest and most abundant atoms in the universe.
  2. Carbon Atoms: These atoms have six protons and can form up to four bonds with other atoms, making them essential for organic compounds and life.
  3. Oxygen Atoms: With eight protons, these atoms are crucial for respiration in living organisms and are a major component of water and many other compounds.
  4. Nitrogen Atoms: These atoms have seven protons and are a key element in proteins and DNA, vital for all living organisms.
  5. Iron Atoms: These atoms contain 26 protons and are important for forming the core of the Earth and for biological processes like oxygen transport in blood.

Examples of Atoms

  1. Hydrogen (H)
  2. Helium (He)
  3. Lithium (Li)
  4. Beryllium (Be)
  5. Boron (B)
  6. Carbon (C)
  7. Nitrogen (N)
  8. Oxygen (O)
  9. Fluorine (F)
  10. Neon (Ne)
  11. Sodium (Na)
  12. Magnesium (Mg)
  13. Aluminum (Al)
  14. Silicon (Si)
  15. Phosphorus (P)
  16. Sulfur (S)
  17. Chlorine (Cl)
  18. Argon (Ar)
  19. Potassium (K)
  20. Calcium (Ca)
  21. Scandium (Sc)
  22. Titanium (Ti)
  23. Vanadium (V)
  24. Chromium (Cr)
  25. Manganese (Mn)
  26. Iron (Fe)
  27. Cobalt (Co)
  28. Nickel (Ni)
  29. Copper (Cu)
  30. Zinc (Zn)

Examples of Atom in Real Life

  1. Hydrogen (H): Found in water (H₂O) and in most organic compounds.
  2. Oxygen (O): Present in the air we breathe and in water (H₂O).
  3. Carbon (C): Found in all living organisms, diamonds, and graphite.
  4. Iron (Fe): Used in construction materials like steel and found in hemoglobin in blood.
  5. Calcium (Ca): Essential for bones and teeth, found in dairy products and leafy greens.
  6. Sodium (Na): Common in table salt (NaCl) and necessary for nerve function.
  7. Chlorine (Cl): Used in disinfectants and also part of table salt (NaCl).
  8. Nitrogen (N): Makes up about 78% of the Earth’s atmosphere and is found in proteins.
  9. Silicon (Si): Found in sand and used in electronics and computer chips.
  10. Copper (Cu): Used in electrical wiring and plumbing materials.

History of Atom

The history of the atom begins in ancient Greece around 450 BCE when philosopher Democritus proposed that matter consists of small, indivisible particles called atoms. However, it wasn’t until the early 19th century that the atomic theory gained scientific footing. In 1803, John Dalton revived the concept, suggesting that each element is composed of unique atoms and that chemical reactions involve the rearrangement of these atoms.

In the early 20th century, discoveries accelerated. J.J. Thomson discovered the electron in 1897, revealing that atoms were divisible and contained smaller particles. Ernest Rutherford’s gold foil experiment in 1911 uncovered the nucleus, a dense central core within the atom. Later, Niels Bohr proposed a model in 1913 where electrons orbit the nucleus in defined paths. This model laid the groundwork for the modern quantum mechanical model of the atom, which describes electrons in probabilistic terms rather than fixed orbits.

Structure of Atom


An atom has a nucleus at its center, which contains protons and neutrons. Protons are positively charged particles, while neutrons have no charge. Electrons, which are negatively charged, orbit the nucleus in regions called electron shells or energy levels. The number of protons defines the element, while the arrangement of electrons determines the atom’s chemical properties. This simple structure—nucleus with protons and neutrons, surrounded by electrons—forms the basis of all matter in the universe.

Size of an Atom

Atoms are incredibly small, typically measuring about 0.1 to 0.5 nanometers in diameter. To put this in perspective, a single nanometer is one-billionth of a meter. Despite their minuscule size, atoms consist of even smaller particles: protons, neutrons, and electrons. The nucleus, containing protons and neutrons, is about 100,000 times smaller than the atom itself, while the electrons occupy the vast empty space around the nucleus. This tiny size makes individual atoms invisible to the naked eye, yet they are the fundamental building blocks of all matter.

Properties of Atoms

Physical Properties

  1. Atomic Mass: The mass of an atom, typically measured in atomic mass units (amu).
  2. Atomic Radius: The size of an atom, measured as the distance from the nucleus to the outermost electron shell.
  3. Ionization Energy: The energy required to remove an electron from an atom.
  4. Melting and Boiling Points: The temperatures at which an atom, as part of an element or compound, changes state from solid to liquid (melting) and from liquid to gas (boiling).
  5. Density: The mass of an atom relative to its volume.
  6. Color and Luster: The appearance of an atom, particularly when it forms part of a material, such as the metallic luster of metals.

Chemical Properties

  1. Electronegativity: The tendency of an atom to attract electrons towards itself in a chemical bond.
  2. Electron Affinity: The energy change that occurs when an atom gains an electron.
  3. Valence Electrons: The number of electrons in the outermost shell of an atom.
  4. Reactivity: How easily an atom undergoes chemical reactions, influenced by its electron configuration and energy levels.

What is the Atom for Kids?

An atom is the smallest building block of everything around us. It has a nucleus in the center with tiny electrons orbiting around it.

Where Do Atoms Come From?

Atoms were formed in the early universe after the Big Bang and continue to be created in stars through nuclear reactions.

How Do Atoms Actually Work?

Atoms work by combining with other atoms to form molecules through chemical bonds, creating all substances we see and use.

What is an Atom Made Of?

An atom is made of a nucleus containing protons and neutrons, with electrons orbiting around the nucleus in electron shells.

Are Atoms Energy or Matter?

Atoms are matter, but they also contain energy within their particles and bonds.

What’s Smaller Than an Atom?

Subatomic particles like protons, neutrons, and electrons are smaller than an atom.

What is the Smallest Thing in the Universe?

Quarks and leptons are currently considered the smallest known particles in the universe.

What Are the Rarest Atoms?

The rarest atoms include astatine and francium, which are naturally occurring but very unstable and scarce.

Are Atoms 99.9% Empty Space?

Yes, atoms are 99.9% empty space, with electrons orbiting far from the nucleus, creating this vast empty space.

How Many Atoms Are in a Baby?

A baby contains approximately 10²⁷ atoms, which is a billion times a trillion atoms.

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