What is Atom in Chemistery ?

 An atom is the smallest unit of matter that makes up everything around us.

It is the basic building block of all substances in chemistry.

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An atom is the smallest particle of an element that still keeps its chemical properties.

🔴 Proton

• Charge: Positive (+)
• Location: Inside the nucleus (center of atom)
• Mass: Heavy (about 1 unit)

👉 Protons decide which element an atom is.
Example:

• Hydrogen = 1 proton
• Oxygen = 8 protons

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⚪ Neutron

• Charge: Neutral (0)
• Location: Inside the nucleus
• Mass: Almost same as proton

👉 Neutrons help stabilize the atom (keep nucleus strong).

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🔵 Electron

• Charge: Negative (–)
• Location: Moves around nucleus in shells (energy levels)
• Mass: Very light (almost 0 compared to proton)

👉 Electrons are responsible for:

• Chemical reactions
• Bonding between atoms

Particle	Charge	Location	Mass
Proton	+	Nucleus	Heavy
Neutron	0	Nucleus	Heavy
Electron	–	Outside nucleus	Very light

Structure of an Atom

An atom has three main parts:

1. Protons (+ charge)
   • Found in the center (nucleus)
   • Positive charge
2. Neutrons (no charge)
   • Also in the nucleus
   • Neutral (no charge)
3. Electrons (– charge)
• Move around the nucleus in shells
• Negative charge

The center part is called the nucleus, which contains protons and neutrons.

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🔹 Example

• Hydrogen atom → 1 proton, 1 electron

• Oxygen atom → 8 protons, 8 electrons

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🔹 Important Points

• Atoms combine to form molecules (like Water = H₂O)
• Different atoms = different elements
• Everything (air, water, your body) is made of atoms