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IB DemystifiedMYP Sciences

Elements, compounds and the periodic table

Everything around you, from the air you breathe to the phone in your pocket, is made from about 90 naturally occurring elements. Chemists organise them in the periodic table, which shows patterns so clearly that it even predicted elements before they were discovered.

Recommended for MYP 2 · About 3 lessons · Criteria A, B, C and D

Group 1Group 2Group 3Group 4Group 5Group 6Group 7Group 0Period 1Period 2Period 3Period 4HhydrogenHeheliumLilithiumBeberylliumBboronCcarbonNnitrogenOoxygenFfluorineNeneonNasodiumMgmagnesiumAlaluminiumSisiliconPphosphorusSsulfurClchlorineArargonKpotassiumCacalciummetalnon-metalsemi-metal
Figure 1. The periodic table arranges elements into groups (columns) and periods (rows).
On this page
  1. Learning objectives
  2. Before you start
  3. Key vocabulary
  4. Understanding the ideas
  5. Elements, compounds and mixtures
  6. Elements in the real world
  7. Worked examples
  8. Assessment tips
  9. Check your understanding
  10. Practice questions
  11. Investigation
  12. Criterion-linked questions
  13. Challenge questions
  14. Topic check
  15. Review your mistakes
  16. Your progress

Learning objectives

By the end of this topic you should be able to:

  • describe atoms and elements and use chemical symbols
  • distinguish elements, compounds and mixtures
  • interpret simple chemical formulas
  • use the periodic table: groups, periods, metals and non-metals
  • compare the properties of metals and non-metals
  • analyse data on compound formation and plan fair tests

Before you start

You will use these skills. If any feel shaky, review them first.

  • pure substances and mixtures (see Pure substances, mixtures and separation)
  • physical and chemical changes (see Physical and chemical changes)
  • simple ratios

Key vocabulary

Atom
The smallest particle of an element.
Element
A substance made of only one type of atom.
Compound
Two or more elements chemically joined in fixed proportions.
Chemical formula
Symbols and numbers showing the atoms in a substance, such as H₂O.
Group
A column of the periodic table; elements in a group have similar properties.
Period
A row of the periodic table.

Understanding the ideas

  1. What is it?

    All matter is made of atoms. An element contains only one type of atom and has its own symbol, such as O for oxygen and Na for sodium. When elements react, their atoms join to form compounds, which have different properties from the elements they came from.

  2. Why does it happen?

    A chemical formula shows which atoms a compound contains and how many: H₂O has two hydrogen atoms and one oxygen atom. Compounds always contain elements in fixed proportions, unlike mixtures, which can be separated by physical methods.

  3. How do we know?

    In 1869 Dmitri Mendeleev arranged the elements so that similar ones fell into the same columns, leaving gaps for undiscovered elements and predicting their properties. Today's periodic table has metals on the left, non-metals on the right, and groups of elements that behave alike.

  4. Why does it matter?

    Knowing the properties of elements helps us choose materials, from copper wires to helium balloons, and to recycle scarce elements used in electronics.

  5. What does it connect to?

    This topic leads to atomic structure, groups and trends, chemical equations and reactions in later chemistry, and links to nutrition (minerals such as iron and iodine) in biology.

Elements, compounds and mixtures

  • Element: one type of atom (Fe, O₂, He).
  • Compound: different elements chemically joined in fixed proportions (H₂O, NaCl, CO₂); properties differ from its elements; separated only by chemical reactions.
  • Mixture: substances not chemically joined; keep their own properties; separated by physical methods.
  • Metals (left): shiny, conduct heat and electricity, malleable, mostly high melting points.
  • Non-metals (right): mostly dull, poor conductors, brittle when solid; many are gases.

Elements in the real world

Copper is used for wires because it conducts well; aluminium is used for aircraft because it is light and strong. Many countries add iodine compounds to salt and iron to flour. Old phones are a rich source of gold, copper and cobalt if they are recycled properly.

Worked examples

Example 1: counting atoms

How many atoms are in one molecule of ammonia, NH₃?

  1. N = 1 nitrogen atom.
  2. H₃ = 3 hydrogen atoms.
  3. Total = 4 atoms.

Example 2: predicting from a group

Chlorine is in group 7 and reacts with sodium. Predict what fluorine will do.

  1. Fluorine is also in group 7.
  2. Elements in the same group have similar properties.
  3. Fluorine will also react with sodium (in fact, even more vigorously).

Assessment tips

Questions on elements and compounds often use formulas, the periodic table and property data. Expect to:

  • Classify substances as elements, compounds or mixtures.
  • Interpret formulas and count atoms.
  • Use the periodic table to predict properties.
  • Process reaction data using conservation of mass.

Common mistakes: thinking a compound keeps the properties of its elements; calling O₂ a compound; confusing groups (columns) with periods (rows); and assuming every conductor is a metal.

Check your understanding

Quick questions on the ideas above. Try each one before using a hint.

Practice questions

Show

Investigation: metal or non-metal?

Partially guided investigation · about 40 minutes · pairs

Research question
Can you decide whether six unknown elements are metals or non-metals by testing their properties?
Scientific background
Metals are usually shiny, conduct electricity and can be bent or hammered. Non-metals are usually dull, do not conduct, and are brittle when solid.
Hypothesis
Write your own prediction, with a scientific justification.
Variables
Identify your independent, dependent and control variables, and explain how you will control them.
Apparatus
Labelled samples such as copper, zinc, magnesium ribbon, carbon (graphite rod), sulfur lumps and iodine crystals in a sealed tube (teacher only); circuit with battery, bulb and crocodile clips; sandpaper; small hammer and heatproof mat.
Method
  1. Look at each sample and record whether it is shiny (rub gently with sandpaper to remove any coating).
  2. Test whether it conducts electricity using the circuit.
  3. Test whether a small piece bends or breaks when tapped gently (not iodine).
  4. Use all your results to classify each element, and check with the periodic table.

Safety. Wear eye protection. Do not handle iodine, which your teacher will show in a sealed tube. Wash hands after handling samples. Tap gently to avoid flying fragments.

Then evaluate: did any element not fit neatly into one group, and why?

Criterion-linked questions

Criterion B: inquiring and designing

Criterion C: processing and evaluating

Criterion D: reflecting on the impacts of science

Challenge questions

Harder problems in unfamiliar contexts. Plan before you calculate.

Topic check

Five questions picked at random from the whole topic. Take a new set whenever you like.

Review your mistakes

Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.

Your progress

Tracked separately for each skill, on this device only.

SkillCorrectStatus

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