LearnLearn Guide for parents
What's the difference between an element and a compound? A kid-friendly guide
An element is a pure substance made of only one kind of atom, like oxygen or gold. A compound is two or more different elements joined together into something new, like water, which is hydrogen and oxygen. The surprising part, and the part kids remember, is that a compound can be completely unlike the elements it's made from.
Here's the difference in plain words, the everyday compounds kids already know, and a quick quiz to check it stuck.
What is an element?
An element is a substance made of just one kind of atom. Every atom of oxygen is an oxygen atom, and every atom of gold is a gold atom. You can't break an element down into anything simpler with chemistry.
There are 118 known elements, and the periodic table lists every one of them. That's why water isn't on the periodic table: it isn't an element.
What is a compound in chemistry?
A compound forms when atoms of two or more different elements join, or bond, together. The new substance has its own properties.
The best example is table salt. It's made of sodium, a soft metal that reacts violently with water, and chlorine, a poisonous yellow-green gas. Joined together, they make the white crystals you sprinkle on food. Nothing about salt looks or acts like either one.
Compounds also have formulas, a short way of writing which elements are inside and how many atoms of each. H₂O means two hydrogen atoms joined to one oxygen atom.
How is a mixture different from a compound?
In a mixture, things are mixed together but not joined, so you can usually separate them again. Sand and iron filings are a mixture: a magnet pulls the iron right out. Salt water is a mixture too, because if you let the water evaporate, the salt is left behind.
In a compound, the elements are chemically joined, so you can't pull them apart by stirring, filtering or using a magnet. It takes a chemical reaction.
Which everyday compounds can kids spot?
Each of these is made from elements kids can find on the periodic table. In Elemon, the two elements behind most of them are "bond buddies": cards that boost each other when they're on the same team. The cards don't combine in the game; the compound is the real-life reason they're buddies.
| Compound | Elements inside | Formula | Where kids meet it |
|---|---|---|---|
| Water | Hydrogen + oxygen | H₂O | Drinking water, rain, ice |
| Table salt | Sodium + chlorine | NaCl | The salt shaker |
| Carbon dioxide | Carbon + oxygen | CO₂ | The bubbles in soda; the air you breathe out |
| Rust | Iron + oxygen | Fe₂O₃ (with some water) | Old bikes and nails left outside |
| Sand (quartz) | Silicon + oxygen | SiO₂ | Beaches, glass |
| Hydrochloric acid | Hydrogen + chlorine | HCl, dissolved in water | Your stomach makes it to digest food |
| Bone mineral | Calcium + phosphorus, plus oxygen | Calcium phosphate | Bones and teeth |
One that's not a compound: steel. Elemon also pairs iron with carbon as bond buddies because of steel, but steel is an alloy, a mixture of metals (or a metal and a little carbon) blended together rather than chemically joined into one compound. It's a great "odd one out" question for kids who have just learned the difference.
Why don't compounds act like their elements?
When atoms bond, they share or swap some of their outer electrons. That changes how the substance behaves, so the compound gets its own melting point, color, smell and reactions. Hydrogen burns and oxygen helps things burn, but water puts fires out. That one example is usually enough to make the idea click.
Quick quiz: element, compound or mixture?
Cover the answers and try these with your kid.
- Gold. Element: only gold atoms.
- Water. Compound: hydrogen and oxygen joined together.
- Salt water. Mixture: salt dissolved in water, and you can get the salt back by letting the water evaporate.
- Oxygen. Element: only oxygen atoms (even though oxygen atoms pair up as O₂).
- Carbon dioxide. Compound: carbon and oxygen joined together.
- Trail mix. Mixture: you can pick the raisins out.
- Steel. Mixture (an alloy): iron blended with a little carbon.
How can kids practice this?
- Bond hunt with cards: spread out the printable element cards and race to find pairs that make a compound from the table above. The back of each card lists its bonds.
- Play it: in Elemon, choose your five cards and put sodium and chlorine on the same team, or hydrogen and oxygen, and see what their bond move does.
- Kitchen check: put salt in water, stir until it disappears, and ask whether it's a compound or a mixture. Then leave a saucer of salt water on a sunny windowsill and see what's left after a few days.
- Homeschooling? This fits week 3 of our 4-week homeschool periodic table unit.
Frequently asked questions
Is water an element or a compound?
Water is a compound. Each water molecule is two hydrogen atoms joined to one oxygen atom, which is why its formula is H₂O. That's also why water isn't on the periodic table.
Is air a compound?
No, air is a mixture. It's mostly nitrogen and oxygen gas, with a little argon, carbon dioxide and water vapor, all mixed together but not joined into one substance.
Is salt an element?
No. Table salt is a compound called sodium chloride, made of the elements sodium and chlorine joined together.
Want to see bond buddies in a battle? Start a match, or look up any element's bond buddies in the Elemondex.