What is an element?
Look at a spoon of iron filings and a pinch of sulphur powder. Each one looks the same all the way through. Each is made of only one kind of atom. A substance like that is called an element.
- Iron is made only of iron atoms.
- Oxygen gas is made only of oxygen atoms (joined in pairs).
- Water is not an element. It has two kinds of atoms, hydrogen and oxygen. We call it a compound.
An element cannot be broken into simpler substances by chemical methods. There are 118 elements known today. About 90 are found in nature; the rest are made in laboratories.
Chemical symbols
A symbol is a short code for an element. It saves time and works in every language.
Rules, step by step:
- Use the first letter of the name, as a capital: H (hydrogen), C (carbon), O (oxygen).
- If another element already has that letter, add a second letter from the name, in small: Cl (chlorine), Ca (calcium), Mg (magnesium).
- The second letter is never a capital. Co is cobalt. CO is carbon monoxide, a compound of two elements.
A symbol also means one atom of that element. O means one oxygen atom.
Symbols from Latin names
Some elements were known long before modern chemistry. Their symbols come from their old Latin names, so they do not look like the English name.
| Element | Latin name | Symbol |
|---|---|---|
| Sodium | natrium | Na |
| Potassium | kalium | K |
| Iron | ferrum | Fe |
| Copper | cuprum | Cu |
| Silver | argentum | Ag |
| Gold | aurum | Au |
Tip: if a familiar metal has a strange symbol, it probably has a Latin name.
Metals and non-metals
Elements fall into broad kinds. Look at the colours in the 3D.
- Metals (yellow): shiny, bend without breaking, carry heat and electricity. Examples: Na, Mg, Al, Fe, Cu, Au.
- Non-metals (green): usually dull and brittle when solid, poor carriers of electricity (carbon as graphite is an exception). Examples: H, C, N, O, S, Cl.
- Noble gases (blue): non-metal gases that hardly react: He, Ne, Ar.
- In-between (purple): boron and silicon behave a bit like both. They are called metalloids.
Hydrogen sits on the left of the table but is a non-metal.
Periodic table layout
The periodic table is a map of all elements. Elements are placed in order of atomic number, the number of protons in one atom (H = 1, He = 2, Li = 3 ...).
- A row is a period. Period 1 has 2 elements, periods 2 and 3 have 8 each (in the part we show).
- A column is a group. Elements in one column behave in a similar way. Group 1 holds Li, Na, K. Group 18 holds the noble gases He, Ne, Ar.
- Metals are mostly on the left and middle, non-metals on the right.
The full story of groups and trends is in the lesson The periodic table.
Try it
- Name card game: write 10 element names on small cards and their symbols on other cards. Shuffle and match them. Check the Latin six at the end.
- Kitchen hunt (with an adult): read a food packet or a salt packet. Find the symbols Na, K, Ca or Fe in the nutrition table and say the element name.
- Predict then check: before you tap a tile in the 3D, say its symbol aloud. Then tap and see if you were right. Use Quiz me for a game.
Key formulas and definitions
- Element = one kind of atom only
- Symbol = capital letter, or capital + small letter (O, Cl)
- Latin-name symbols: Na (natrium), K (kalium), Fe (ferrum), Cu (cuprum), Ag (argentum), Au (aurum)
- Atomic number = number of protons; the table is ordered by it
- Row = period, column = group
Worked examples
1. Write the symbols of sodium, chlorine and carbon.
Sodium = Na (from natrium). Chlorine = Cl (C is taken by carbon, so add a small l). Carbon = C.
2. Is "CO" the symbol of an element? What about "Co"?
CO has two capital letters, so it is two elements written together: carbon and oxygen (carbon monoxide). Co has a capital then a small letter, so it is one element, cobalt.
3. Out of H, He, Li, Be, B, C, which are metals?
Li and Be are metals. H and C are non-metals, He is a noble gas, and B is a metalloid (in-between).
4. Which element has atomic number 11, and what is its symbol? Why does it not start with S?
Element 11 is sodium, symbol Na. The symbol comes from its Latin name natrium, not from the English name.
Common mistakes
- Writing two capitals: CL, NA or CO for one element. The second letter must be small: Cl, Na, Co.
- Writing all letters small, like na or fe. The first letter is always a capital.
- Thinking every symbol comes from the English name. Na, K, Fe, Cu, Ag and Au come from Latin names.
- Calling water or salt an element. Elements have only one kind of atom; water (H₂O) and salt (NaCl) are compounds.