⭐ Sabse Important Points · एक नज़र में
- Solid: Definite shape and volume, particles closely packed and vibrate about fixed positions.
- Atomic Number (Z): Number of protons in the nucleus; determines the element's identity.
- Liquid: Definite volume but no definite shape, particles are close but can move past each other.
- Mass Number (A): Sum of protons and neutrons in the nucleus.
- Gas: No definite shape or volume, particles are far apart and move randomly at high speed.
- Ionic Bond: Formed by transfer of electrons from a metal to a non-metal (e.g., NaCl).
Introduction · परिचय
Chemistry is a key part of General Science for RRB Group D. This topic covers basic concepts of matter, atoms, molecules, chemical reactions, acids, bases, and salts at the 10th level. Understanding these fundamentals helps in answering direct and conceptual questions.
Matter and Its States
Matter is anything that has mass and occupies space. It exists in three main states: solid, liquid, and gas. The arrangement and movement of particles determine the state. Changes of state occur on heating or cooling.
- Solid
- Melting
- Liquid
- Evaporation
- Gas
- Condensation
- Freezing
- ↺ phir se repeat hota hai
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite | Indefinite | Indefinite |
| Volume | Definite | Definite | Indefinite |
| Particle arrangement | Closely packed | Less closely packed | Far apart |
| Compressibility | Negligible | Low | High |
⭐ Key Points · याद रखने वाली बातें
- Solid: Definite shape and volume, particles closely packed and vibrate about fixed positions.
- Liquid: Definite volume but no definite shape, particles are close but can move past each other.
- Gas: No definite shape or volume, particles are far apart and move randomly at high speed.
- Sublimation: Direct change of solid to gas without passing through liquid state (e.g., camphor, dry ice).
- Latent Heat: Heat energy absorbed or released during a change of state without temperature change.
✍️ Solved Example 1 · हल किया हुआ उदाहरण
❓ Question: Which state of matter has the highest intermolecular space?
✅ Solution: Gas
💡 Explanation: In gases, particles are far apart with negligible intermolecular forces, so intermolecular space is maximum.
Atomic Structure and Chemical Bonding
Atoms are the building blocks of matter. They consist of protons, neutrons, and electrons. The number of protons (atomic number) defines the element. Atoms combine to form molecules through chemical bonds: ionic, covalent, and metallic.
📐 Formula / Rule Box · सूत्र याद रखो
Mass Number
A = Z + n
Number of neutrons
n = A - Z
| Bond Type | Formation | Example |
|---|---|---|
| Ionic | Transfer of electrons | NaCl |
| Covalent | Sharing of electrons | H2O |
| Metallic | Sea of delocalized electrons | Fe, Cu |
⭐ Key Points · याद रखने वाली बातें
- Atomic Number (Z): Number of protons in the nucleus; determines the element's identity.
- Mass Number (A): Sum of protons and neutrons in the nucleus.
- Ionic Bond: Formed by transfer of electrons from a metal to a non-metal (e.g., NaCl).
- Covalent Bond: Formed by sharing of electrons between non-metals (e.g., H2O).
- Valency: Combining capacity of an atom, equal to the number of electrons lost, gained, or shared.
✍️ Solved Example 1 · हल किया हुआ उदाहरण
❓ Question: What is the atomic number of an element with 12 protons and 12 neutrons?
✅ Solution: 12
💡 Explanation: Atomic number is the number of protons, which is 12. The mass number would be 24, but atomic number is 12.
Practice Questions · खुद हल करके देखो
पहले खुद try karo, phir “Answer dekho” dabakar check karo. 👇
Q1Which of the following is a sublimating substance?
👀 Answer dekho
✅ Answer: Camphor
💡 Explanation: Camphor changes directly from solid to gas on heating, which is sublimation. Others like salt and sugar melt into liquid.
Q2The bond formed by sharing of electrons between two atoms is called:
👀 Answer dekho
✅ Answer: Covalent bond
💡 Explanation: Covalent bonds involve sharing of electron pairs, typically between non-metals. Ionic bonds involve transfer.
Q3An atom has 17 protons and 18 neutrons. What is its mass number?
👀 Answer dekho
✅ Answer: 35
💡 Explanation: Mass number = protons + neutrons = 17 + 18 = 35.
⚠️ Common Mistakes · ये गलतियाँ बिल्कुल मत करना
- Confusing atomic number with mass number: Atomic number is only protons, while mass number includes neutrons.
- Assuming all solids are hard: Some solids like sodium are soft; hardness depends on bonding.
- Mixing up ionic and covalent bonds: Ionic involves transfer (metal + non-metal), covalent involves sharing (non-metals).
⚡ Quick Revision · Exam से पहले 2 मिनट में दोहराओ
- States of Matter: Solid (definite shape/volume), Liquid (definite volume), Gas (indefinite).
- Atomic Number: Number of protons; Mass Number: Protons + neutrons.
- Chemical Bonds: Ionic (transfer), Covalent (sharing), Metallic (delocalized electrons).