Trends in Properties of Elements in the Periodic Table
Senior 2 · Chemistry
Trends in Properties of Elements in the Periodic Table
Lesson 4 of 4
20 min
Rwanda is one of the world's important sources of tungsten, tin and tantalum. In 2019 it was the seventh-largest producer of tungsten in the world, and it supplies about 9 per cent of the world's tantalum. The tin ore mined here is cassiterite (tin(IV) oxide, SnO2), the tantalum ore is coltan, and the tungsten ore is wolframite.
Why do phone makers want tantalum, and why do drill makers want tungsten? Every use of an element depends on its properties. An engineer, a builder or a farmer who understands the link between properties and uses can choose the right material and explain the choice.
By the end of this lesson you will be able to compare metals and non-metals in one table and justify the uses of common elements.
| Metals | Non-metals | |
|---|---|---|
| Outer electrons | Usually 1, 2 or 3 | Usually 4 to 7 (8 for noble gases) |
| Ions formed | Positive ions (cations) by losing electrons, e.g. Na+, Mg2+, Al3+ | Negative ions (anions) by gaining electrons, e.g. Cl−, O2− |
| Oxides | Basic (alkaline if soluble) | Acidic or neutral |
| With dilute acids | Those above hydrogen give a salt + hydrogen | No reaction to give hydrogen |
| Compounds with each other | Mixtures of metals form alloys | Covalent compounds, e.g. CO2, H2O |
| Physical properties | Lustrous, malleable, ductile, conductors | Dull, brittle solids, insulators; many are gases |
| Element | Property used | Use |
|---|---|---|
| Aluminium | Low density; resists corrosion (oxide layer); good conductor | Roofing sheets, saucepans, window frames, overhead power cables |
| Copper | Excellent electrical conductor; very ductile | Electrical wiring in houses, motors and phone chargers |
| Iron (as steel) | Strong and cheap | Building bars, bridges, hoes, machetes, vehicles |
| Zinc | More reactive than iron, so it corrodes first and protects it | Coating iron roofing sheets (galvanising), dry cells |
| Tin | Resists corrosion; low melting point | Coating steel food cans; solder for joining electronic parts |
| Tungsten | Highest melting point of all metals (about 3420 °C); very hard | Filament lamps, drill tips and cutting tools |
| Tantalum | Very resistant to corrosion; forms a thin insulating oxide | Tiny capacitors in phones and laptops |
| Gold and silver | Very unreactive; lustrous; excellent conductors | Jewellery; contacts in electronics |
| Carbon | Graphite: soft, conducts; diamond: hardest; charcoal: burns | Pencils and electrodes; cutting tools; fuel |
| Nitrogen | Needed by plants; unreactive gas | Making fertilisers (ammonium nitrate, urea); keeping packaged food fresh |
| Oxygen | Supports breathing and burning | Hospital oxygen, welding and cutting torches |
| Chlorine | Kills bacteria | Treating drinking water; making PVC pipes |
| Sulfur | Reacts to form sulfuric acid | Making sulfuric acid and fertilisers; hardening rubber |
| Phosphorus | Needed by plants | Phosphate fertilisers such as DAP; matches |
| Silicon (metalloid) | Semiconductor | Solar cells and computer chips |
| Argon and helium | Unreactive; helium is very light | Filling light bulbs; filling balloons |
An alloy is a mixture of a metal with other elements, made to improve its properties. Pure iron is fairly soft, but adding a little carbon makes steel, which is much harder and stronger. Brass (copper and zinc) is harder than copper and does not tarnish easily, and solder (mainly tin) melts at a low temperature, so it can join wires without damaging them.
Copper is a better conductor than aluminium, yet the long overhead power lines between towns are made of aluminium (around a steel core). Explain why.
Solution. A cable hanging between pylons must be light, or the pylons would have to be much stronger and closer together. Aluminium is about one-third as dense as copper, so for the same electrical resistance an aluminium cable is much lighter. Aluminium is also cheaper, and its oxide layer protects it from rain. The steel core gives the cable strength. Inside buildings, where weight does not matter and space is limited, copper is used because it conducts better for the same thickness.
Tip
Exam technique: always link a use to a property with the word "because". Half an answer says "Copper is used for wiring." A full answer says "Copper is used for electrical wiring because it is a very good conductor of electricity and is ductile, so it can be drawn into thin wires."
Try each item before you read the solution.
Iron roofing sheets are coated with zinc. Explain why, using the reactivity series.
Solution: Zinc is more reactive than iron. It keeps the air and water away from the iron, and even if the coating is scratched, the zinc corrodes in preference to the iron, so the iron does not rust.
Give one use each of tungsten and tantalum and the property that makes each suitable.
Solution: Tungsten is used for lamp filaments and drill tips because it has the highest melting point of any metal and is very hard. Tantalum is used in capacitors in phones because it resists corrosion and forms a thin insulating oxide layer.
Why is gold used for jewellery while iron is not?
Solution: Gold is very unreactive, so it stays shiny and does not corrode or react with sweat. Iron rusts in air and moisture, so iron jewellery would soon turn brown.
Why is chlorine, not fluorine, used to treat drinking water?
Solution: Chlorine kills bacteria at small, controlled concentrations. Fluorine is the most reactive non-metal of all; it attacks almost everything, including water and pipes, and is far too dangerous to handle.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
