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Introduction to Matter and Energy

In our environment, all entities can be categorized into two primary categories: matter and energy.

  • Matter: Defined as substances that occupy space and possess mass.
  • Energy: Defined as entities that do not occupy space and lack mass.

Classification of Matter

Matter is classified based on its physical properties and chemical composition:

  1. Pure substances: Consist of only one type of particle.
  2. Non-pure substances (Mixtures): Comprised of two or more substances that are not chemically bonded.
       - Elements: Fundamental substances that consist of only one type of atom.
         - Examples include:
           - Iron (Fe)
           - Oxygen (O₂)
           - Copper (Cu)
           - Nitrogen (N)
       - Compounds: Substances formed when two or more elements are chemically bonded.
         - Examples include:
           - Water (H₂O)
           - Carbon dioxide (CO₂)
       - Homogeneous mixtures: Mixtures that are uniform in composition.
         - Examples include:
           - Salt solution
           - Sugar solution
       - Heterogeneous mixtures: Mixtures with a non-uniform composition.
           - Examples include:
             - Lime + Water
             - Rice + Sand

Phases of Matter

  • Solid: Has a definite shape and volume.
  • Liquid: Has a definite volume but takes the shape of its container.
  • Gas: Fills the entire volume of its container and has no definite shape.

Atomic Structure

Atoms are the fundamental building blocks of matter.

  • Atoms consist of subatomic particles:
      - Protons: Positively charged particles located in the nucleus.
      - Neutrons: Neutral particles located in the nucleus.
      - Electrons: Negatively charged particles that orbit around the nucleus.
      - Charge Overview:
        | Particle | Location | Charge | Mass (relative to proton) |
        |-------------|----------------|--------------|---------------------------|
        | Protons | Nucleus | +1 | 1 |
        | Neutrons | Nucleus | 0 | 1 |
        | Electrons | Around nucleus | -1 | 1/1840 |
Charge Neutrality
  • The number of electrons in an atom is equal to the number of protons, resulting in the atom being electrically neutral.

Atomic Models

To better understand the arrangement of these particles, atomic models have been introduced:

  1. Nuclear Model (Ernest Rutherford):
       - The nucleus is a compact center of the atom that contains protons and neutrons.
       - Relative size analogy: if the atom were the size of a football field, the nucleus would be smaller than a chickpea.

  2. Planetary Model (Ernest Rutherford):
       - Electrons move around the nucleus, similar to planets revolving around the Sun.
       - Although attracted by the positive charge of the nucleus, electrons do not spiral into the nucleus due to their rapid movement.

  3. Bohr Model:
       - Further explains that electrons move in defined paths or shells around the nucleus.
       - Energy levels are assigned (n=1, 2, 3, 4) starting closest to the nucleus, with each level having specific energy, increasing as they move away from the nucleus.

Maximum Number of Electrons per Energy Level:

   - First energy level: 2 electrons
   - Second energy level: 8 electrons
   - Third energy level: 18 electrons (8 often considered for basic structure)

Atomic Number and Mass Number

  1. Atomic Number (Z): The number of protons in the nucleus of an atom, represented as Z = p.
  2. Mass Number (A): The total number of protons and neutrons in the nucleus, represented as A = p + n.
  3. Standard way of writing:
       - If the symbol of an atom is X, then:
       - Notation:
    extXextA<em>extZext{X}^{ ext{A}}<em>{ ext{Z}}    - Example: Carbon with atomic number 6 and mass number 12 is represented as:      extC12</em>6ext{C}^{12}</em>{6}

Ions Formation

  • Positive Ions: Formed by removing electrons.
      - Notation: X → X^+ + e
      - Example:
        - Sodium (Na): ext{Na}
    ightarrow ext{Na}^+ + e
        - Magnesium (Mg): ext{Mg}
    ightarrow ext{Mg}^{2+} + 2e

  • Negative Ions: Formed by gaining electrons.
      - Notation: X + e → X^-
      - Example:
        - Fluorine (F): ext{F} + e
    ightarrow ext{F}^-
        - Oxygen (O): ext{O} + 2e
    ightarrow ext{O}^{2-}

Electronic Configuration

The arrangement of electrons in an atom's energy levels, starting from the one closest to the nucleus, is known as electronic configuration.

  • E.g.,
       | Atomic Number | Element | Electronic Configuration |
       |----------------|---------------|-------------------------|
       | 1 | Hydrogen (H) | 1 |
       | 2 | Helium (He) | 2 |
       | 3 | Lithium (Li) | 2,1 |
       | 4 | Beryllium (Be) | 2,2 |
       | 5 | Boron (B) | 2,3 |
       | 6 | Carbon (C) | 2,4 |
       | … | … | … |
Modern Periodic Table
  • The modern periodic table is based on atomic numbers (increasing order) and electronic configuration.
  • The periodic law states that properties of elements are periodic functions of their atomic number, meaning elements with similar properties recur regularly.

Elements Classification

  • Metals, Non-metals, and Metalloids: Roughly, 80% of identified elements are metals.

Physical Properties of Metals:

   - Metallic lustre
   - Sonorous
   - Solid state at room temperature (except mercury which is liquid)
   - Malleable and ductile
   - Good conductors of heat and electricity

Chemical Properties of Metals:

   - Forms positive ions (cations) by losing electrons
   - Combines with oxygen to produce basic oxides

Non-Metals Properties

Physical Properties:

   - Lack metallic lustre
   - Generally brittle
   - Poor conductors of heat and electricity

Chemical Properties:

   - Forms negative ions (anions)
   - Many oxides of non-metals are acidic.

Conclusion

These foundational concepts paint a comprehensive picture of chemical properties, atomic structures, and classifications necessary for the understanding of matter and energy in a broader scientific context.