Chemistry: Atoms, Reactions, and Why Things Explode

Warm-Up: Periodic Table Scavenger Hunt

1. What is the lightest metal on the periodic table?
2. What is the heaviest naturally occurring noble gas?
3. Name an element that was named after a planet.
4. Which element has the chemical symbol W, and why is it not what you would expect?
5. Find two elements named after scientists.
6. What element is a liquid at room temperature (besides mercury)?

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Core Lesson: The Building Blocks of Matter

Atomic Structure

Everything around you — the air, the water, the screen you are reading this on — is made of atoms. An atom is incredibly small: about 100 million atoms lined up would span 1 centimeter.

Every atom has three types of subatomic particles:

| Particle | Charge | Location | Mass | |----------|--------|----------|------| | Proton | Positive (+1) | Nucleus (center) | 1 amu | | Neutron | Neutral (0) | Nucleus (center) | 1 amu | | Electron | Negative (-1) | Orbiting the nucleus | ~0 (1/1836 amu) |

• Protons determine which element an atom is.
• Neutrons add mass but do not change the element. Atoms of the same element with different numbers of neutrons are called isotopes (e.g., Carbon-12 and Carbon-14).
• Electrons determine how the atom interacts with other atoms — they are responsible for chemical bonds.

The Periodic Table as an Organizing Tool

The periodic table is not just a list — it is a map of patterns. Elements are arranged by:

• Rows (periods): Each new row adds a new electron shell.
• Columns (groups): Elements in the same column have similar chemical behavior because they have the same number of valence electrons (electrons in the outermost shell).

Key groups to know:

| Group | Name | Properties | Examples | |-------|------|-----------|----------| | 1 | Alkali metals | Very reactive, soft, one valence electron | Li, Na, K | | 2 | Alkaline earth metals | Reactive, two valence electrons | Mg, Ca | | 17 | Halogens | Very reactive nonmetals, one electron short of full shell | F, Cl, Br | | 18 | Noble gases | Almost completely unreactive (full outer shell) | He, Ne, Ar |

Chemical Reactions: Rearranging Atoms

A chemical reaction is a process where atoms are rearranged into new combinations. The key principle is:

Consider the reaction of hydrogen gas burning in oxygen:

Unbalanced: H2 + O2 --> H2O

Count the atoms:

• Left side: 2 H, 2 O
• Right side: 2 H, 1 O

The oxygen is unbalanced! We fix it:

Balanced: 2H2 + O2 --> 2H2O

Now count again:

• Left side: 4 H, 2 O
• Right side: 4 H, 2 O

Exothermic vs. Endothermic

• Exothermic reactions release energy (usually as heat). The products have less energy than the reactants. Example: burning wood, explosions, hand warmers.
• Endothermic reactions absorb energy. The products have more energy than the reactants. Example: ice melting, photosynthesis, cold packs.

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Hands-On Lab: Vinegar and Baking Soda

The Reaction

When vinegar (acetic acid) meets baking soda (sodium bicarbonate), they react to produce carbon dioxide gas, water, and sodium acetate:

CH3COOH + NaHCO3 --> CO2 + H2O + CH3COONa

We will capture the CO2 gas in a balloon and investigate how changing the amounts of reactants affects how much gas is produced.

Experiment: Varying the Ratio

Setup: For each trial, put vinegar in the bottle, put baking soda in the balloon (using the funnel), then stretch the balloon over the bottle opening and tip the baking soda into the vinegar.

| Trial | Vinegar | Baking Soda | Prediction | |-------|---------|-------------|------------| | 1 | 50 mL | 1 teaspoon (~5 g) | ? | | 2 | 50 mL | 2 teaspoons (~10 g) | ? | | 3 | 50 mL | 4 teaspoons (~20 g) | ? |

Before running each trial, write down your prediction: Will the balloon be bigger, smaller, or the same as the previous trial?

What to Observe and Record

1. Balloon size: Which trial produced the biggest balloon? Why?
2. Temperature: Touch the bottle during the reaction. Does it feel warm or cold?
3. Mass conservation: If you weigh the entire setup (bottle + balloon + contents) before and after the reaction on a closed system, does the mass change? (It should not! The CO2 is captured in the balloon.)

Discussion Questions

• Why does the balloon inflate? (CO2 gas is produced, and gases expand to fill their container.)
• Why does the bottle feel cold? (The reaction is endothermic — it absorbs heat from its surroundings.)
• If the system were truly closed (no gas escaped), would the mass before and after be the same? (Yes — conservation of mass.)

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Challenge: Balancing Equations

Level 1 — Straightforward:

1. ___ Fe + ___ O2 --> ___ Fe2O3
2. ___ H2 + ___ Cl2 --> ___ HCl
3. ___ Na + ___ H2O --> ___ NaOH + ___ H2

Level 2 — Trickier:

4. ___ C3H8 + ___ O2 --> ___ CO2 + ___ H2O
5. ___ Al + ___ HCl --> ___ AlCl3 + ___ H2

Level 3 — Boss Fight:

6. ___ Fe2O3 + ___ CO --> ___ Fe + ___ CO2

Bonus Question: Why Can't You Turn Lead into Gold?

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Resources

• Periodic Table — Ptable.com — beautiful interactive periodic table with detailed info on every element
• PhET: Balancing Chemical Equations — practice balancing with this interactive simulation
• Crash Course Chemistry — full video series covering all major chemistry topics
• The Elements by Theodore Gray — stunning photo book companion site showing every element
• Tyler DeWitt Chemistry Videos — fun, clear explanations of chemistry concepts