🔷 What is the Periodic Table?
The Periodic Table of Elements is a chart that organizes all known chemical elements based on their atomic number, electron configuration, and recurring chemical properties.
📌 Created by: Dmitri Mendeleev in 1869
🧩 Structure of the Periodic Table
| Part of Table | Description |
|---|---|
| Periods (rows) | Horizontal lines (1 to 7); show energy levels (electron shells) |
| Groups (columns) | Vertical columns (1 to 18); elements in the same group have similar properties |
| Metals | On the left; shiny, conduct electricity, often solid |
| Nonmetals | On the right; gases or brittle solids, poor conductors |
| Metalloids | In between; have properties of both metals and nonmetals |
🌟 Important Groups
| Group Name | Number | Example Elements | Properties |
|---|---|---|---|
| Alkali metals | 1 | Na, K | Very reactive, soft metals |
| Alkaline earth | 2 | Ca, Mg | Reactive metals |
| Halogens | 17 | F, Cl, I | Very reactive nonmetals |
| Noble gases | 18 | He, Ne, Ar | Very stable, do not react easily |
| Transition metals | 3–12 | Fe, Cu, Zn | Good conductors, form colorful compounds |
⚛️ Atomic Number and Mass
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Atomic number = number of protons (defines the element)
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Atomic mass = protons + neutrons (average mass of the atom)
🔗 What is Chemical Bonding?
Chemical bonding is how atoms connect to form molecules or compounds by sharing or transferring electrons.
🔵 Types of Chemical Bonds
| Bond Type | How It Works | Example |
|---|---|---|
| Ionic Bond | One atom transfers electrons to another | NaCl (salt) |
| Covalent Bond | Atoms share electrons | H₂O (water), CO₂ |
| Metallic Bond | Electrons move freely between metal atoms | Iron, Copper |
💡 More About Each Bond
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Ionic Bonds:
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Between metals and nonmetals
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Forms ions (charged atoms): cations (+), anions (–)
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Strong bond, forms crystals (e.g. table salt)
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Covalent Bonds:
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Between nonmetals
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Can be single, double, or triple bonds (sharing 1, 2, or 3 pairs)
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Examples: water (H₂O), methane (CH₄), oxygen gas (O₂)
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Metallic Bonds:
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Between metal atoms
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Electrons are free to move → good conductivity and malleability
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🧪 Why Do Atoms Bond?
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To become more stable
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Most atoms want a full outer electron shell (8 electrons – "octet rule")
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Noble gases already have this, which is why they don’t react much
✅ Summary
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The Periodic Table organizes elements by atomic number and properties
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Elements in the same group have similar chemical behavior
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Chemical bonds form so atoms can become more stable
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Main bond types: Ionic, Covalent, and Metallic