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1. Atomic Structure

The atomic structure is like the blueprint of an atom, which is the smallest unit of matter that makes up everything around us.

• What is an Atom?
  An atom is made up of three main particles:
  • Protons: Positively charged particles located in the nucleus (the center of the atom).
  • Neutrons: Neutral particles (no charge) also found in the nucleus.
  • Electrons: Negatively charged particles that orbit around the nucleus in shells or energy levels.
  • 

How is an Atom Structured?

• The nucleus (center of the atom) contains protons and neutrons.
• The electrons move around the nucleus in orbits (like planets orbiting the sun). These orbits are divided into energy levels (shells).
• The number of protons in the nucleus determines what element the atom is. For example:
  • Hydrogen has 1 proton,
  • Oxygen has 8 protons.

Atomic Number and Mass Number

• The atomic number is the number of protons in an atom, which also equals the number of electrons in a neutral atom.
• The mass number is the total number of protons and neutrons in an atom.

Example:

• In a Carbon (C) atom:
  • Atomic number = 6 (because it has 6 protons)
  • Mass number = 12 (because it has 6 protons and 6 neutrons)

2. Organic Chemistry

Organic chemistry is the branch of chemistry that studies carbon-based compounds. Almost all living things are made up of organic compounds, so organic chemistry is very important for life.

• What Makes a Compound Organic?
  A compound is organic if it contains carbon atoms. In organic compounds, carbon atoms bond with other elements, such as hydrogen, oxygen, nitrogen, etc.

Key Features of Organic Compounds:

• Carbon atoms can form strong bonds with other carbon atoms, which allows for the creation of large and complex molecules (like those in living organisms).
• Organic compounds can be simple (like methane – CH₄) or complex (like DNA – a huge molecule with carbon atoms).

Common Organic Compounds:

1. Hydrocarbons: Compounds made only of carbon and hydrogen. They can be:
   • Alkanes: Simple hydrocarbons with single bonds, e.g., methane (CH₄).
   • Alkenes and Alkynes: Hydrocarbons with double or triple bonds, e.g., ethene (C₂H₄) or ethyne (C₂H₂).
2. Functional Groups: These are specific groups of atoms that give compounds their chemical properties. For example:
   • Alcohols (contains –OH group, like ethanol (C₂H₅OH)).
   • Carboxylic Acids (contains –COOH group, like acetic acid (CH₃COOH)).

Why is Organic Chemistry Important?

• Life: All living organisms are made from organic compounds (like proteins, fats, and sugars).
• Everyday Products: Things like plastics, medicines, food, and fuels are made from organic chemistry.

3. Chemical Reactions

A chemical reaction happens when substances change into new substances. This happens because the atoms of the original substances rearrange to form new substances with different properties.

What Happens During a Chemical Reaction?

• Bonds Break: The bonds between atoms in the reactants (starting substances) are broken.
• New Bonds Form: New bonds are made between the atoms to create the products (new substances).

Basic Types of Chemical Reactions:

1. Combination Reaction: Two or more substances combine to form one new substance.
   • Example:
     $2H_2 + O_2 → 2H_2O$ 

     (Hydrogen + Oxygen = Water)

2. Decomposition Reaction: A single substance breaks down into two or more simpler substances.
   • Example:
     $2H_2O_2 → 2H_2O + O_2$ 

     (Hydrogen Peroxide breaks down into Water and Oxygen)

3. Displacement Reaction: One element displaces another in a compound.
   • Example:
     $Zn + CuSO_4 → ZnSO_4 + Cu$ 

     (Zinc displaces copper from copper sulfate)

4. Combustion Reaction: A substance reacts with oxygen to produce heat and light.
   • Example:
     $CH_4 + 2O_2 → CO_2 + 2H_2O$ 

     (Methane + Oxygen = Carbon dioxide + Water + Heat)

Balancing Chemical Equations:

In a chemical reaction, the number of atoms of each element must be the same on both sides of the equation. This is called balancing the equation. For example:

• In the reaction
  $2H_2 + O_2 → 2H_2O$ 

  there are 4 hydrogen atoms and 2 oxygen atoms on both sides, so it’s balanced.

Why are Chemical Reactions Important?

• Energy Production: Reactions like combustion (burning fuel) release energy that powers cars, factories, and homes.
• Life Processes: Many reactions happen inside our bodies (like digestion), helping us live and function.
• Everyday Products: Chemical reactions are used to make everything from soap to medicines to cleaning products.

Key Takeaways

1. Atomic Structure:
   • Atoms are made of protons, neutrons, and electrons.
   • The atomic number tells you how many protons are in an atom, which determines the element.
2. Organic Chemistry:
   • The study of carbon-based compounds.
   • Organic compounds are the building blocks of life and many everyday products.
3. Chemical Reactions:
   • Chemical reactions change substances by rearranging atoms.
   • There are different types of reactions like combination, decomposition, displacement, and combustion.