Atoms, bonding and reactions for high-school chemistry: study cards over three tiers, the tricky ones, a practice quiz at three levels — Foundation, On-Level, and Challenge — and a lab where you label oxygen's orbital diagram, sort twelve unfamiliar substances by bond type from the formula alone, put the six steps of predicting a reaction in order, and argue from bond energies where the heat of a gas stove really comes from. Work here, or print it and use a pencil — both count.
Two atoms held together. To pull them apart you have to PUT energy in — breaking always costs.
Breaking a bond COSTS energy; forming one RELEASES it. “Bonds store energy” is backwards. A reaction gives off heat when the bonds it forms release more than the bonds it broke cost — which is why fuels are made of weak bonds and burn into strong ones.
What people get wrong
⚠️People often think…
A molecule with polar bonds is a polar molecule.
Shape decides. CO₂ has two strongly polar bonds pointing in exactly opposite directions, so they cancel and the molecule is nonpolar. Water’s two bonds point the same general way, so they add up. Draw it before you call it.
Polar bonds can cancel. Draw the shape.
⚠️People often think…
Anything with hydrogen in it can hydrogen bond.
The hydrogen has to be attached to N, O or F — the three atoms electronegative enough to strip it nearly bare. CH₄ is full of hydrogen and does none of it, which is why methane is a gas and water is a liquid.
Only H on N, O or F.
⚠️People often think…
A catalyst increases the amount of product you get.
It lowers the activation energy, so you get there faster — and it speeds the reverse reaction by exactly as much. The equilibrium position and the products are untouched. A catalyst buys time, not yield.
Faster, not more.
⚠️People often think…
At equilibrium the reaction has stopped.
Both directions are still running full speed — they are just running at the SAME speed, so the amounts stop changing. Label a few atoms and you would watch them cross back and forth forever.
Equal rates, not zero rates.
Configuration, shape, force, energy
1Watch one
Why is water a liquid at room temperature when methane is a gas?
Both molecules are small and light — size is not the answer.
Look at where the hydrogen sits. In water it is on oxygen; in methane it is on carbon.
H on O means hydrogen bonding — strong attractions holding the molecules together.
Water molecules cling; methane molecules barely notice each other, so it boils far below room temperature. ✓
2Do one with me
Fill in what energy and shape do.
Forming a bond does this with energy:
CO₂ has polar bonds but the molecule is
A catalyst changes the speed but not the
💬One sentence, then you move on
Why is “bonds store energy” backwards?
3Try one
Which orbital fills first, 4s or 3d?
I want a hint first
Electrons fill lowest energy first. On the diagonal diagram, one of these two comes earlier than its shell number suggests.
💬Last one — then you're done here
Why can a reaction be at equilibrium and still be running?
Where this goes
Where this lives
Why a hand warmer gets hot, why oil and water separate, why a catalytic converter cleans exhaust without being consumed, why ice floats.
What this feeds
Next unit is stoichiometry and solutions — putting numbers on all of it.
Name one thing that gets hot or cold on its own when mixed.
One card at a time — tap “Show me” to check yourself, then Next. Start at Foundation; when those feel easy, climb.
Helpful Hints
🪜 Atoms to reactions — the ladder
Electrons fill orbitals lowest-energy first, one per box before pairing → the configuration is the element’s address on the table → inner electrons shield, so effective nuclear charge sets every trend: radius, ionization energy, electronegativity → who gives, shares or pools electrons decides ionic, covalent or metallic → polarity and intermolecular forces set melting and boiling → five reaction types predict products → heat is bonds broken minus bonds formed, speed is collisions, and the endpoint is equilibrium.
Everything in this unit follows from where the outer electrons are and how hard the nucleus holds them. Get the configuration right and the trends, the bonds, the shapes and the reactions fall out of it.
It is all the outer electrons.
⚠️ Tricky ones
Breaking a bond COSTS energy. Forming a bond RELEASES it. “Bonds store energy” is the classic wrong idea.
4s fills BEFORE 3d. The configuration order is energy order, not shell order.
A polar BOND does not make a polar MOLECULE. CO₂ has two polar bonds and is nonpolar — the shape cancels them.
Lone pairs shape the molecule but don’t appear in its name. Water is “bent,” not “tetrahedral,” though it has four pairs.
Hydrogen bonding needs H on N, O or F. CH₄ has hydrogen and no hydrogen bonds.
A catalyst speeds a reaction but does NOT change the products or the equilibrium position.
At equilibrium the reaction has not stopped — both directions run at the same rate.
🔀 The five reaction types — the chart
Type
Pattern
How to recognize it
Example
synthesis
A + B → AB
two things become one
2Mg + O₂ → 2MgO
decomposition
AB → A + B
one thing becomes two, usually with heat or electricity
CaCO₃ → CaO + CO₂
single replacement
A + BC → AC + B
a free element and a compound; check the activity series
Zn + 2HCl → ZnCl₂ + H₂
double replacement
AB + CD → AD + CB
two compounds swap partners; look for a precipitate, gas or water
AgNO₃ + NaCl → AgCl↓ + NaNO₃
combustion
fuel + O₂ → CO₂ + H₂O
a hydrocarbon and oxygen; always exothermic
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Name the type from the reactants, and the products write themselves.
🎯 How the test will ask
“Write the electron configuration and draw the orbital diagram for sulfur. How many unpaired electrons?”
“Rank Na, Mg, Cl by atomic radius and by ionization energy, and explain with effective nuclear charge.”
A Lewis structure — “identify the shape, the bond angle, and whether the molecule is polar.”
Bond energies in a table — “calculate ΔH and state whether the reaction is exothermic.”
Reactants only — “classify the reaction, predict the products, balance.”
“The system is at equilibrium; pressure is increased. Predict the shift and explain.”
✅ Can you…
Write a configuration, draw the orbital diagram, and count unpaired electrons?
Explain all three periodic trends with one idea — effective nuclear charge?
Predict a molecule’s shape and polarity from its Lewis structure?
Rank boiling points by intermolecular force?
Compute ΔH from bond energies and get the sign right?
Classify five reactions from reactants alone and predict a shift with Le Châtelier?
Pick your level
Look back at anything you missed — the hint that appeared is exactly what to reread tonight.
How sure did you feel?
Lab
Work like a scientist: label the diagrams, turn the table into a graph, then write a claim with evidence and reasoning. Every lab checks itself on the spot, and hints are free.
Your practice never leaves this device. There is no account and no sign-in. Your work is saved in this browser only, and you can erase it whenever you want.
Your practice record — saved on this device
This is your record of the module on screen — it stays here and goes nowhere. Independent means you got it right on the first tap; supported means you got it after the explain-and-retry, or marked ‘I had it’ on a revealed answer. Both count, and neither is a grade. If your teacher asks, copy the row or show them this screen.
Date
—
Topic
—
Level
—
Independent
0 of 0
Supported
0 of 0
Hints used
0
Cards studied
0
Lab
—
Traps met
0
Explained in own words
0
Confidence
—
The answer key is for a teacher: it prints only from here, for the unit on screen. Print the study packet prints the study pages and a blank quiz — never the answers.