1. What is an Atom?
● Atom: The smallest building block of all matter. Everything you see, touch, and breathe is
made of atoms.
● Element: A pure substance made of only one type of atom (e.g., Gold, Oxygen, Carbon).
2. The 3 Subatomic Particles
An atom is made of three even smaller particles. Use this quick summary to remember them:
Particle Charge Location Relative Mass
Proton ➕ Positive (+1) Inside the Nucleus (center) Heavy (1 amu)
Neutron ⚪ Neutral (0) Inside the Nucleus (center) Heavy (1 amu)
Electron ➖ Negative (-1) Orbiting around the nucleus Extremely light (~0)
3. Reading the Periodic Table (The Cheat Sheet)
Every element on the periodic table gives you a recipe for its atoms. For example, look at
Carbon:
● Atomic Number: The number of protons (and electrons in a neutral atom). Carbon's
atomic number is 6, so it has 6 protons.
● Mass Number: The total number of Protons + Neutrons.
● How to find Neutrons: Subtract the atomic number from the mass number.
𝑁𝑒𝑢𝑡𝑟𝑜𝑛𝑠 = 𝑀𝑎𝑠𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 − 𝐴𝑡𝑜𝑚𝑖𝑐 𝑁𝑢𝑚𝑏𝑒𝑟
4. How the Atomic Model Changed (Timeline)
● Atom: The smallest building block of all matter. Everything you see, touch, and breathe is
made of atoms.
● Element: A pure substance made of only one type of atom (e.g., Gold, Oxygen, Carbon).
2. The 3 Subatomic Particles
An atom is made of three even smaller particles. Use this quick summary to remember them:
Particle Charge Location Relative Mass
Proton ➕ Positive (+1) Inside the Nucleus (center) Heavy (1 amu)
Neutron ⚪ Neutral (0) Inside the Nucleus (center) Heavy (1 amu)
Electron ➖ Negative (-1) Orbiting around the nucleus Extremely light (~0)
3. Reading the Periodic Table (The Cheat Sheet)
Every element on the periodic table gives you a recipe for its atoms. For example, look at
Carbon:
● Atomic Number: The number of protons (and electrons in a neutral atom). Carbon's
atomic number is 6, so it has 6 protons.
● Mass Number: The total number of Protons + Neutrons.
● How to find Neutrons: Subtract the atomic number from the mass number.
𝑁𝑒𝑢𝑡𝑟𝑜𝑛𝑠 = 𝑀𝑎𝑠𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 − 𝐴𝑡𝑜𝑚𝑖𝑐 𝑁𝑢𝑚𝑏𝑒𝑟
4. How the Atomic Model Changed (Timeline)
