“If you want to understand the universe, think in terms of atoms, energy, and relationships.”
Nikola Tesla
If you zoomed in far enough on anything, you’d find the same basic building blocks: atoms. They’re insanely small, but they hold the universe together. In this lesson, we’ll explore what atoms are made of, how they differ, and how we organize them on the periodic table.
What Is an Atom?
An atom is the smallest unit of an element that still keeps the properties of that element. It’s like a LEGO block: simple on its own, but capable of forming complex things when combined.
Atoms are made of three main particles:
| Particle | Charge | Location | Role |
| Proton | + Positive | In the nucleus | Determines the element’s identity |
| Neutron | 0 Neutral | In the nucleus | Adds mass, stabilizes the nucleus |
| Electron | – Negative | Orbiting the nucleus | Involved in chemical bonding and reactivity |
Fun Fact: Atoms are 99.9999% empty space. If the nucleus were a golf ball, the nearest electron could be over a mile away.
Atomic Number, Mass Number & Isotopes
These three terms are often confused, so let’s break them down clearly:
Atomic Number:
- The number of protons in the nucleus
- Unique to each element
- Determines the element’s identity
→ Hydrogen = 1 proton = atomic number 1
Mass Number:
- Total number of protons + neutrons
→ If Carbon has 6 protons and 6 neutrons, its mass number is 12.
Isotopes:
- Atoms of the same element with different numbers of neutrons
- They behave the same chemically but have different masses
Example:
Carbon-12 = 6 protons + 6 neutrons
Carbon-14 = 6 protons + 8 neutrons (used in carbon dating!)
⚖️ Ions: Charged Atoms
If an atom gains or loses electrons, it becomes an ion.
| Type of Ion | How It Forms | Charge | Example |
| Cation | Loses electrons | + | Na⁺ (sodium) |
| Anion | Gains electrons | – | Cl⁻ (chloride) |
Ions are important in literally everything.
The Periodic Table
The periodic table is like a map: it shows how elements are organized based on their properties and atomic structure.
Quick Starter Tips:
- Each box shows an element’s symbol, name, atomic number, and atomic mass.
- Rows are called periods and show increasing atomic number.
- Columns are called groups or families and contain elements with similar behavior.
Why Atomic Structure Matters
Understanding atoms is the key to understanding chemistry.
- How atoms bond? That’s in the electrons.
- Why some elements explode in water and others don’t? That’s due to their structure.
- Why are you alive and breathing? Because of perfectly arranged atoms in your body.
Everything starts with the atom.
Some Notes and Recap:
| Concept | What It Means |
| Atom | Smallest unit of matter |
| Proton | Positive, in nucleus, defines the element |
| Neutron | Neutral, in nucleus, adds mass |
| Electron | Negative, outside nucleus, key in bonding |
| Atomic Number | Number of protons |
| Mass Number | Protons + neutrons |
| Isotope | Same element, different neutrons |
| Ion | Charged atom (from losing/gaining electrons) |
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