# Reading the Periodic Table

> How the table is arranged, groups and periods, metals and non-metals, and the main families of elements.

From HSC Chemistry on WhizzNotes, free study notes for NSW students: https://whizznotes.com/chemistry/periodic-table/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: Mendeleev's card game
In 1869 a Russian chemistry teacher, Dmitri Mendeleev, was writing a textbook. He made a card for each of the 63 elements known then, with its mass and properties, and laid them out like a game of patience.

When he lined them up by mass, elements with similar properties kept appearing at regular intervals. So he arranged them in rows and columns. Where the pattern broke, he did something bold: he left **gaps** and said, "An element that has not been found yet belongs here."

He even predicted what those missing elements would be like. Within 20 years gallium, scandium and germanium were discovered, and they matched his predictions almost exactly. His table became the map of chemistry.

**In short:** The periodic table arranges the elements in order of atomic number. Rows (periods) have the same number of electron shells, columns (groups) have the same number of valence electrons and similar properties, and metals sit on the left with non-metals on the right.

## How the table is arranged

Today the elements are arranged in order of **atomic number** (number of protons), not mass.

- A **period** is a **row** across. There are 7 periods. Elements in the same period have the **same number of electron shells**.
- A **group** is a **column** down. There are 18 groups. Elements in the same group have the **same number of valence electrons**, so they have **similar chemical properties**.

*Diagram: Simplified periodic table outline: metals on the left, non-metals on the right, noble gases in the last column, and metalloids along the staircase between metals and non-metals*
*The first five periods, simplified. Metals on the left, non-metals on the right, metalloids along the staircase.*

## Reading one box

Each box usually shows:

- The **symbol**, one or two letters. The first is a capital, the second lower case: Co is cobalt, but CO is carbon monoxide.
- The **atomic number** (whole number, smaller).
- The **relative atomic mass** (often a decimal, larger).
- The name.

Some symbols come from Latin names: Na (natrium, sodium), K (kalium, potassium), Fe (ferrum, iron), Cu (cuprum, copper), Ag (argentum, silver), Au (aurum, gold), Pb (plumbum, lead).

## Metals, non-metals and metalloids

A **staircase line** runs from boron down to astatine. Metals are to the left, non-metals to the right.

| Property | Metals | Non-metals |
|---|---|---|
| Look | Shiny (lustrous) | Dull |
| State at room temperature | Solid (except mercury) | Many are gases. Bromine is a liquid |
| Conduct heat and electricity | Yes, well | No (except graphite, a form of carbon) |
| Bend or hammer into shape | Yes: **malleable** and **ductile** | No, solids are **brittle** |
| Ions formed | Positive | Negative |

**Metalloids** such as silicon and germanium sit along the staircase and have some properties of both. Silicon is a **semiconductor**, which is why it is used in computer chips.

## Families of elements

| Group | Family name | Valence electrons | Behaviour |
|---|---|---|---|
| 1 | **Alkali metals** (Li, Na, K) | 1 | Soft, very reactive, react with water to make hydrogen and an alkali. Stored under oil |
| 2 | **Alkaline earth metals** (Mg, Ca) | 2 | Reactive, but less than group 1 |
| 3 to 12 | **Transition metals** (Fe, Cu, Zn, Ag) | varies | Hard, strong, high melting points, coloured compounds, used as catalysts |
| 17 | **Halogens** (F, Cl, Br, I) | 7 | Reactive non-metals, exist as pairs ($\mathrm{Cl_2}$), form salts with metals |
| 18 | **Noble gases** (He, Ne, Ar) | full shell | Unreactive gases. Used in signs and light globes |

### Key idea: Same group, same behaviour
Lithium, sodium and potassium all fizz on water and make a hydroxide and hydrogen, because each has **1 valence electron** to lose. If you know how one member of a group reacts, you can predict the others.

### Exam tip: Hydrogen is a loner
Hydrogen sits above group 1 because it has 1 electron, but it is a **non-metal gas** and is not an alkali metal.

### Watch out: Rows and columns
Students often mix these up. **P**eriods go across like a sentence that ends with a **p**eriod (full stop). **G**roups go down.

**Mind map**

```text
Periodic table
  Arranged by
    Atomic number
    Mendeleev left gaps
  Periods
    Rows
    Same number of shells
  Groups
    Columns
    Same valence electrons
    Similar properties
  Types
    Metals: left
    Non-metals: right
    Metalloids: staircase
  Families
    Group 1: alkali metals
    Group 2: alkaline earth
    Group 17: halogens
    Group 18: noble gases
```

### Year 11: Blocks of the table
The table can be split into **blocks** that match the subshell being filled by the last electron.

- **s-block**: groups 1 and 2 (and helium).
- **p-block**: groups 13 to 18.
- **d-block**: the transition metals, groups 3 to 12.
- **f-block**: the lanthanides and actinides, the two rows usually printed below the main table.

So the shape of the periodic table is really a map of electron configurations. The period number tells you the highest shell. The block tells you which subshell is filling.

### Year 12: Why transition metals are special
Transition metals have partly filled **d subshells**. This gives them:

- **Several possible ions**: iron forms $\mathrm{Fe^{2+}}$ and $\mathrm{Fe^{3+}}$, copper forms $\mathrm{Cu^{+}}$ and $\mathrm{Cu^{2+}}$. Roman numerals show which: iron(III) oxide is $\mathrm{Fe_2O_3}$.
- **Coloured compounds**: d electrons absorb some colours of visible light. Copper(II) sulfate solution is blue.
- **Catalytic activity**: they can easily change charge, so they help reactions along. Iron is the catalyst in making ammonia. Platinum and palladium are used in car catalytic converters.

## Quick summary

- Elements are arranged by **atomic number**. Mendeleev made the first useful table and left gaps for undiscovered elements.
- **Periods** are rows (same number of shells). **Groups** are columns (same valence electrons, similar properties).
- Metals are on the left, non-metals on the right, metalloids on the staircase.
- Group 1 alkali metals, group 2 alkaline earth metals, groups 3 to 12 transition metals, group 17 halogens, group 18 noble gases.

## Quiz

Try these questions from the chapter quiz.

1. Elements in the modern periodic table are arranged in order of:
   - A. Atomic mass
   - B. Atomic number
   - C. Date of discovery
   - D. Number of neutrons
   - Answer: B. Atomic number. Atomic number (protons) gives the order.

2. A vertical column in the periodic table is called a:
   - A. Group
   - B. Period
   - C. Block
   - D. Row
   - Answer: A. Group. Columns are groups. Rows are periods.

3. Elements in the same group have the same number of:
   - A. Shells
   - B. Neutrons
   - C. Valence electrons
   - D. Protons
   - Answer: C. Valence electrons. That is why they have similar chemical properties.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/chemistry/periodic-table/#quiz