Chemistry Course – General Introduction  

What Is Chemistry?

Chemistry is the science that studies matter, its composition, structure, properties, and the transformations it undergoes.

👉 In short: chemistry explains what things are made of and how they interact with each other.

2️⃣ States of Matter

All matter is made of atoms. It can exist in different states:

• Solid → fixed shape and volume (e.g., ice).
• Liquid → fixed volume but variable shape (e.g., water).
• Gas → no fixed shape or volume (e.g., water vapor).
• Plasma → ionized gas, present in stars.

3️⃣ The Atom

The atom is the smallest unit of a chemical element.

It consists of:

• Nucleus → protons (+) and neutrons (0).
• Electron shells → electrons (–) orbiting the nucleus.

Atomic number (Z) = number of protons.

Mass number (A) = protons + neutrons.

4️⃣ The Periodic Table

The periodic table organizes all chemical elements.

• Rows (periods) → show the number of electron shells.
• Columns (groups) → contain elements with similar properties (e.g., alkali metals, halogens, noble gases).

5️⃣ Chemical Bonds

Atoms combine to form molecules through bonds:

• Ionic bond → electron transfer (NaCl).
• Covalent bond → electron sharing (H₂O, CO₂).
• Metallic bond → delocalized electrons in metals.

6️⃣ Chemical Reactions

A chemical reaction transforms reactants into products.

Example:

2H2+O2→2H2O2H₂ + O₂ → 2H₂O2H2​+O2​→2H2​O

Characteristics:

• Atoms are conserved (nothing is lost, nothing is created).
• Bonds are rearranged.
• Energy is released or absorbed.

7️⃣ Applications of Chemistry

Chemistry is everywhere:

• Health → medicines, vaccines.
• Energy → batteries, fuels.
• Environment → water treatment, recycling.
• Food → additives, preservation.

8️⃣ Simple Exercises

1. Determine the number of protons, neutrons, and electrons in a carbon atom (C, Z=6, A=12).
2. Write the combustion reaction of methane (CH₄).
3. Identify the type of bond in NaCl and H₂O.