Lecture on Atoms and Their Structure

Introduction to Atoms

• Everything is made up of atoms, whether living or non-living.
• Atoms are extremely small; a single cell can contain over 100 trillion atoms.
• Atoms consist of smaller particles: a central nucleus and electrons orbiting in shells.

Structure of an Atom

• Nucleus: Contains two types of particles:
  • Protons: Positive charge (+1)
  • Neutrons: No charge (neutral)
• Electrons: Orbit the nucleus, negative charge (-1)
  • Electrons have a mass 2,000 times smaller than protons and neutrons.
• Despite visual representations, electrons and nucleus are much smaller than depicted.

Properties of Atomic Particles

• Protons: Relative mass of 1, positive charge.
• Neutrons: Relative mass of 1, no charge.
• Electrons: Very small mass (often considered zero), negative charge.
• Atoms are mostly empty space, resembling a solar system structure.

Atomic Size and Charge

• Atomic radius is approximately 0.1 nanometers.
• Nucleus is 10,000 times smaller than the atom.
• Atoms are neutral when the number of protons equals electrons.
• Atoms that lose or gain electrons become ions (charged atoms):
  • Negative Ion: More electrons than protons.
  • Positive Ion: More protons than electrons.

Periodic Table Overview

• Each element is represented by a box in the periodic table, called nuclear symbols.
  • Elemental Symbol: One or two-letter symbol for the element (e.g., O for Oxygen, Li for Lithium).
  • Atomic Number: Number of protons in an atom, determining the element.
  • Mass Number: Total number of protons and neutrons.

Examples

• Oxygen: Atomic number 8 (8 protons), mass number 16 (8 neutrons).
• Lithium: Atomic number 3 (3 protons), mass number 7 (4 neutrons).

Additional Resources

• Videos, questions, flashcards, and past exams available at cognito.org.
• Track progress and study recommendations available on the website.