An atom is the smallest unit of matter that still keeps the properties of an element. Everything around us — air, water, plants, even you — is made up of atoms.
🧬 Basic Structure of an Atom
An atom is made of three main subatomic particles:
| Particle | Charge | Location | Mass (approx.) |
|---|---|---|---|
| Proton | Positive (+) | In the nucleus | 1 atomic unit (amu) |
| Neutron | Neutral (0) | In the nucleus | 1 atomic unit (amu) |
| Electron | Negative (−) | Orbiting the nucleus | ~0 (very small mass) |
🔵 Nucleus
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Center of the atom
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Contains protons and neutrons
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Very dense and heavy
🟢 Electron Shells / Orbitals
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Electrons move in paths (like planets around the sun)
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These orbits are called shells or energy levels
🔢 Atomic Number and Mass
| Term | Meaning |
|---|---|
| Atomic Number | Number of protons in the atom (also = number of electrons) |
| Mass Number | Protons + Neutrons |
Example:
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Carbon has 6 protons, 6 neutrons → Mass = 12
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Atomic Number = 6
🧪 Isotopes
Atoms of the same element with different numbers of neutrons.
Example:
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Carbon-12 and Carbon-14 are both carbon, but one is radioactive.
⚛️ Atoms and Elements
An element is a substance made of only one type of atom.
| Element | Symbol | Atomic Number |
|---|---|---|
| Hydrogen | H | 1 |
| Oxygen | O | 8 |
| Gold | Au | 79 |
🔗 How Do Atoms Combine?
Atoms bond to form:
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Molecules: two or more atoms joined (e.g. H₂O = water)
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Compounds: molecules made from different elements (e.g. CO₂)
Types of chemical bonds:
| Bond Type | Description |
|---|---|
| Ionic | Transfer of electrons |
| Covalent | Sharing of electrons |
| Metallic | Electrons move freely between atoms |
🌍 Importance of Atoms
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They make everything in the universe.
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Understanding atoms helps in chemistry, physics, biology, medicine, and engineering.
🧠 Fun Facts
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There are more atoms in a glass of water than stars in the universe!
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A single human body contains around 7 octillion (7×10²⁷) atoms.
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Atoms are mostly empty space — the nucleus is tiny, but very heavy.