Quick Review of Middle School Science
15min Part 0 / Ch0 / Lesson 2
Prerequisites: 0-0-1
Objectives
- Recall the basic concepts of atoms, molecules, and ions
- Review how to read chemical equations
- Confirm element symbols and basic chemical formulas
Atoms, Molecules, and Ions
Atom = the smallest particle of an element. Molecule = a particle formed by bonded atoms. Ion = an atom (or group) that has gained or lost electrons, giving it an electric charge.
Essential Element Symbols
| Element | Symbol | Element | Symbol | Element | Symbol |
|---|---|---|---|---|---|
| Hydrogen | H | Carbon | C | Nitrogen | N |
| Oxygen | O | Sodium | Na | Magnesium | Mg |
| Aluminum | Al | Silicon | Si | Phosphorus | P |
| Sulfur | S | Chlorine | Cl | Potassium | K |
| Calcium | Ca | Iron | Fe | Copper | Cu |
| Zinc | Zn | Silver | Ag | Gold | Au |
Reading Chemical Equations
In a chemical equation, the left side shows the reactants and the right side shows the products:
Reading: “Two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water.”
Coefficients in a chemical equation show the ratio of molecules. The type and number of atoms are the same on both sides (conservation of mass).
| Symbol | Meaning |
|---|---|
| → | reacts to form |
| + | and (between reactants or products) |
| Coefficients (2, 3, etc.) | Ratio of molecules |
| (s), (l), (g), (aq) | Solid, liquid, gas, aqueous solution |
Check Your Understanding
Q1 What is the chemical formula for water?
Q2 In 2H₂ + O₂ → 2H₂O, what does the coefficient '2' represent?
Q3 What kind of particle is Na⁺?