Introduction to Chemistry

Introduction to Chemistry

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Basics of Matter and Energy

  • Matter:
    • Definition: Anything that takes up space and has mass.
    • States: Matter can exist in three states – solid, liquid, or gas.
  • Energy:
    • Definition: The ability to do work, such as maintaining homeostasis in the body.

Elements and Atoms

  • Element:
    • Definition: One of the basic building blocks of matter.
    • Relationship to the periodic table: Elements are represented on the periodic table.
    • Atom:
    • Definition: The smallest complete unit of an element, with distinct physical and chemical properties.

Common Elements in the Body

  • The four most abundant elements in the human body are:
    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)
    • Nitrogen (N)
  • These elements are essential for all forms of life.

Organic Molecules

  • Definition: Molecules that contain carbon and hydrogen, essential for forming living organisms.

Foundation of Chemistry

  • Understanding the composition and interactions of matter forms the basis of chemistry.

Structure of Atoms

  • Atoms are the smallest complete units of matter.
    • Quote: "I could be anything I wanted, so I became everything."

Subatomic Particles

  • Constituents of Atoms:
    • Atoms consist of smaller particles known as subatomic particles which have properties of mass and charge.
  • Mass:
    • Definition: The amount of matter present in an atom.
    • Calculated by summing the number of protons and neutrons (p + n).
    • Electrons contribute negligible mass.
    • Mass of particles:
      • Proton: 1
      • Neutron: 1
      • Electron: 0

Charge of Subatomic Particles

  • Charge:
    • Positive (+), negative (-), or neutral (0).
  • Interactions:
    • Like charges repel.
    • Opposite charges attract.
  • Particle charge:
    • Proton: Positive (+)
    • Neutron: Neutral
    • Electron: Negative (-)

Atomic Structure

  • Location of Particles:
    • Protons and neutrons reside in the nucleus, while electrons form a cloud surrounding the nucleus.
  • Electron Arrangement:
    • The innermost shell holds a maximum of 2 electrons. Subsequent shells can hold up to 8 electrons each.
    • A full outer shell indicates an atom is stable, adhering to the Octet Rule.

Periodic Table of Elements

  • Each cell contains:
    • Symbol of the element
    • Atomic number (smaller number, indicates number of protons)
    • Atomic mass (larger number, sum of protons and neutrons)
  • Atomic Number:
    • Defines the element, remains unchanged in chemical reactions.
    • In neutral atoms: number of protons = number of electrons.
  • Atomic Mass:
    • Atomic mass number = protons + neutrons.

Isotopes

  • Definition: Atoms of the same element that have a different number of neutrons and consequently different masses.
  • Some isotopes are radioactive and useful as tracers in medical imaging.

Molecules

  • Definition: A chemical unit formed when two or more atoms bond together through chemical reactions.

Chemical Bonds

  • Atoms bond to achieve full outer shells yielding molecules or compounds, represented by chemical formulas.
  • Example: Water (H₂O) indicates two hydrogen (H) atoms and one oxygen (O) atom.

Chemical Equations

  • Shorthand representation of chemical reactions:
    • Reactants yield products.
    • Example: C + O₂ → CO₂.

Chemical Bonds - Overview

  • Types of Bonds:
    • Ionic Bonds:
    • Formation involves the transfer of electrons leading to charged ions that attract each other due to opposite charges.
    • Covalent Bonds:
    • Formation involves the sharing of valence electrons between atoms to achieve a full outer shell.

Ionic Bonds

  • Transfer of electrons leads to:
    • Formation of a positive ion (loss of electrons) ➔ e.g., Na⁺
    • Formation of a negative ion (gain of electrons) ➔ e.g., Cl⁻
  • Example: Sodium donates an electron to Chlorine, satisfying both atoms' octet rule.

Covalent Bonds

  • Atoms share valence electrons, thereby achieving stable outer shells.
  • Representation: Shared electrons depicted as solid lines connecting atoms.

The Importance of Water in Life

  • Water constitutes a significant proportion of living cells and body weight.
  • **Structure of Water:
    • The structure leads to unique properties essential for life.**

Polar Covalent Bonds

  • These bonds occur with unequal sharing of electrons, resulting in molecules with partial charges:
    • One side is slightly positive while the other is slightly negative.
  • Water as an example:
    • Oxygen end has a partial negative charge, while hydrogen ends have a partial positive charge (δ+ and δ-).

Hydrogen Bonds

  • Weak bonds formed between water molecules due to polarity.
  • Responsible for water's unique properties such as:
    • Liquid state at room temperature.
    • High specific heat.
    • Ice being less dense than liquid water.
    • Water as a solvent in chemical reactions of life.

Acids and Bases

  • Water dissociates into hydrogen ions (H⁺) and hydroxide ions (OH⁻) during chemical reactions.
  • Acids:
    • Substances that release hydrogen ions or absorb hydroxide ions.
  • Bases:
    • Substances that absorb hydrogen ions or release hydroxide ions.

pH Scale

  • Indicator of acidity or basicity (alkalinity) with a range of 0 to 14.
    • pH 7 is neutral (e.g., distilled water).
    • pH <7 indicates acidity.
    • pH >7 indicates basicity.
  • Maintaining physiological pH (around 7.4) is crucial for health.
  • Buffers help in minimizing pH changes in biological systems.