Elements and the Periodic Table
In 2002, Russian physicist Yuri Oganessian's team at JINR created element 118 — oganesson — by firing calcium ions for 1,080 hours straight, adding the last tile to a 150-year-old chart that organises all known matter.
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Q1 · Name 5 things you use every day that are made from elements. What do you know about where those elements come from?
Q2 · If you had to sort all 118 elements into groups, what feature would you use to sort them?
● Know
- What an element is and why it can't be broken down further
- The meaning of symbol, period and group on the periodic table
- The location of metals, non-metals and metalloids on the periodic table
● Understand
- Why elements in the same group behave similarly
- Why elements in the same period have the same number of electron shells
- How the position of an element in the table predicts its properties
● Can do
- Read a periodic table entry (atomic number, symbol, name)
- Identify the period and group of an element from the table
- Predict chemical behaviour based on group membership
- Element
- Symbol
- Period
- Group
- Periodic table
- Horizontal row — same number of electron shells
- Pure substance made of one type of atom
- Chart organising all elements by atomic number
- Vertical column — same number of outer electrons
- One or two letter shorthand for an element
Rip a piece of aluminium foil. Cut it again and again — keep going. No matter how small your piece gets, each fragment is still aluminium. If you could keep going until you reached a single atom, that atom would still be aluminium. That's what an element is: a substance made of only one type of atom, which cannot be chemically broken down any further.
Key ideas about elements:
- There are about 118 known elements. 94 occur naturally on Earth; the rest have been made artificially in laboratories.
- Each element has a unique symbol: one or two letters (always start with a capital). Some symbols come from Latin names — Fe (iron, from ferrum), Au (gold, from aurum), Na (sodium, from natrium).
- Every substance you've ever touched is made of elements, or combinations of elements bonded together.
Australian connection: Australia is one of the world's leading exporters of iron ore (iron, Fe) mined in the Pilbara, Western Australia; bauxite (aluminium ore, Al) from Cape York, Queensland; and copper (Cu) from Olympic Dam, South Australia. Each of these mining operations is chasing a specific element because that element has unique properties that make it valuable.
| Element | Symbol | Where found in Australia | Why it matters |
|---|---|---|---|
| Iron | Fe | Pilbara, WA | Steel production, construction |
| Aluminium | Al | Cape York, QLD (as bauxite) | Lightweight metal for transport |
| Copper | Cu | Olympic Dam, SA | Electrical wiring |
| Gold | Au | Kalgoorlie, WA | Electronics, jewellery |
| Uranium | U | South Australia | Nuclear fuel |
An element is a substance made of only one type of . It be broken down chemically. There are about known elements, and each has a unique of one or two letters.
The periodic table is the most important chart in all of science. It arranges all 118 elements so that the ones with similar properties line up together. Here's how to read it:
- 7 periods (rows) — numbered 1 to 7 from top to bottom. Period 1 has only 2 elements (H and He); Period 2 has 8 elements.
- 18 groups (columns) — numbered 1 to 18 from left to right. Groups are also called families because the elements in them behave like relatives.
- Special group names: Group 1 = alkali metals (Li, Na, K…); Group 17 = halogens (F, Cl, Br…); Group 18 = noble gases (He, Ne, Ar…).
Each element box in the table shows at least three things:
- Atomic number — the number of protons in one atom (top of box).
- Symbol — the 1–2 letter code (centre, large).
- Name — the full element name (bottom of box).
Metals occupy the left and centre of the table. Non-metals are on the upper right. A zigzag "staircase" line separates them, and the elements that sit on the staircase are called metalloids (they have properties of both).
The periodic table isn't just a list — it's a map of patterns. The position of an element tells you about its structure and behaviour:
- Period number = number of electron shells. Sodium (Na) is in Period 3, so a sodium atom has 3 electron shells. Oxygen (O) is in Period 2, so it has 2 shells.
- Group number (Groups 1–2 and 13–18) = number of electrons in the outer shell. Lithium (Li, Group 1) has 1 outer electron. Oxygen (O, Group 16) has 6 outer electrons.
- Same group = similar chemical behaviour. The outer electrons control how an element reacts. Elements with the same number of outer electrons react in similar ways.
Examples of group patterns:
| Group | Family name | Behaviour pattern | Examples |
|---|---|---|---|
| 1 | Alkali metals | All react vigorously with water, producing hydrogen gas | Li, Na, K, Rb |
| 17 | Halogens | All react with metals to form salts; all are non-metals | F, Cl, Br, I |
| 18 | Noble gases | All are extremely unreactive (stable outer shell) | He, Ne, Ar, Kr |
This predictive power is why Dmitri Mendeleev (the scientist who created the modern periodic table in 1869) was able to predict the existence of elements that hadn't been discovered yet — he left gaps where the patterns said an element should exist.
Sodium (Na) is in Group 1 of the periodic table. Potassium (K) is also in Group 1. Predict: will potassium react with water? Will it behave in a similar way to sodium — or very differently? Give a reason based on what you've learned about groups.
How close was your prediction?
Great — you used the "same group = similar behaviour" rule correctly.
Key takeaway: same group = same number of outer electrons = similar chemical behaviour.
Use a copy of the periodic table (or the information from this lesson) to answer the following for each element listed below. For each one, write: (a) the period number, (b) the group number, (c) whether it is a metal, non-metal or metalloid.
| Element | Symbol | Period | Group | Metal / Non-metal / Metalloid |
|---|---|---|---|---|
| Lithium | Li | |||
| Chlorine | Cl | |||
| Argon | Ar | |||
| Silicon | Si | |||
| Calcium | Ca |
Choose THREE elements from the Australian mining table in Card 4. For each one, research or recall:
- Its symbol and atomic number.
- What period and group it belongs to.
- One physical property that makes it useful (e.g., conducts electricity, is lightweight, is strong).
- One product made from it that you might find in your home or school.
Q1. Name the element with symbol Au and explain why it is used in jewellery. (2 marks)
Q2. Explain the difference between a group and a period on the periodic table. (3 marks)
Q3. Sodium (Na) is in Group 1 and Period 3. Explain what each of those positions tells you about the structure of a sodium atom. (4 marks)
Answers
▾MCQ 1
B — An element is a pure substance that cannot be broken down further by chemical means. Solids, compounds and metal mixtures (alloys) are not the same as elements.
MCQ 2
C — Fe comes from the Latin word ferrum, meaning iron. This is why the symbol doesn't match the English name. Fluorine is F, Francium is Fr, and Fermium is Fm.
MCQ 3
C — Elements in the same group have the same number of outer electrons, which causes them to react in similar ways. They do NOT necessarily have the same mass, the same number of shells (that's the period), or the same state at room temperature.
MCQ 4
C — The period number equals the number of electron shells in an atom of that element. The atomic number (number of protons) is read from the element box, not the period. Metals/non-metals are determined by position, not period alone.
MCQ 5
B — Na, Mg, Al, Si, P, S, Cl, Ar are the elements in Period 3 — they all have 3 electron shells. Period 2 starts with Li; Period 4 starts with K; Period 1 has only H and He.
Short Answer 1
Model answer: Au is the symbol for gold (from Latin aurum). Gold is used in jewellery because it is a shiny, attractive metal that does not tarnish or corrode — it stays looking beautiful for a very long time. It is also rare, which adds to its value. (1 mark for naming gold; 1 mark for a valid property reason.)
Short Answer 2
Model answer: A group is a vertical column in the periodic table. Elements in the same group have the same number of outer electrons, which makes them behave chemically in similar ways (1 mark). A period is a horizontal row. Elements in the same period have the same number of electron shells (1 mark). The key difference is the direction — groups go down, periods go across — and what they tell you: groups predict chemical behaviour, periods tell you about shell number (1 mark).
Short Answer 3
Model answer: Group 1 tells me that sodium has 1 outer electron in its outermost shell (1 mark). This means it will behave like the other Group 1 elements (alkali metals) — it will be reactive and will donate that 1 electron easily, for example reacting vigorously with water (1 mark). Period 3 tells me that sodium has 3 electron shells in total (1 mark). That means sodium's electrons are arranged across 3 shells: 2 in the first shell, 8 in the second shell, and 1 in the third (outermost) shell (1 mark for full description).
Earlier you were asked: If you had to sort all 118 elements into groups, what feature would you use?
Now that you've worked through the lesson, write a more complete answer. Explain what feature scientists actually used, and why that feature (outer electrons / electron shells) is so powerful for predicting behaviour.
- An element is a pure substance made of one type of atom — it cannot be broken down chemically.
- The periodic table has 7 periods (rows) and 18 groups (columns); each element box shows atomic number, symbol and name.
- Period = number of electron shells; Group (1–2 and 13–18) = number of outer electrons → similar chemical behaviour in same group.