Basic Technology
JSS 3 – First Term
Week 7
Topic: Identification of Metals
Outline:
- Meaning of metals
- Properties of metals
- Forms of metals
Meaning of Metals
We have been discussing several materials that are very essential in the construction of technology, and this week we are going to be discussing another important material which is metal. Metals are another material used in the construction of things and they can be identified using their identity, colour/lustre, fusibility, magnetic effect, conduction of heat and sound.
A metal is a material (an element, compound, or alloy) that is typically hard when in a solid state, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable—that is, they can be hammered or pressed permanently out of shape without breaking or cracking—as well as fusible (able to be fused or melted) and ductile (able to be drawn out into a thin wire). About 91 of the 118 elements in the periodic table are metals; the others are nonmetals or metalloids. Some elements appear in both metallic and nonmetallic forms.
Scientist use the term “metal” to collectively describe all elements other than hydrogen and helium, the simplest two, in a star. The star fuses smaller atoms, mostly hydrogen and helium, to make larger ones over its lifetime. In that sense, the metallicity of an object is the proportion of its matter made up of all heavier chemical elements, not just traditional metals.
Many elements and compounds that are not normally classified as metals become metallic under high pressures; these are formed as metallic allotropes of nonmetals.
The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, non-illuminated signs and railroad tracks. Precious metals were historically used as coinage.
Properties of identification of metals
Density
This property describes how heavy or light is a given substance. Density is measured by dividing the mass of the metal by one cubic metre of that metal. For instance, 1 cubic metre of steel weighs 8000 kilograms. That means, the density of steel is 8000kg/m3. The density of water is 1000kg/m while aluminium has a density of 2800kg/m3. That means aluminium is lighter than steel but heavier than water. Plastics are much lighter with a density of 900kg/m3.
Colour/Lustre
When a material is polished, it shines. Different metals show different colours when they are polished.
Fusibility
Metals can be melted until they become liquid. The temperature is at which solid metal melts is called the melting point. This temperature is different for different metals e.g. for cast iron, the melting point is 1241oC, while it is 2005oC for wrought iron.
Magnetic Effect of Metal
When a magnet picks or sticks to a material, the material is said to be magnetic. Non metals are generally non-magnetic. For example, wood, ceramics, plastic,etc. are not magnetic. Also, not all metals are magnetic. Only metals that have iron in them are magnetic. These metals are called ferrous metals. Other metals are called non-ferrous metals.
Conductivity of Heat
A heat exchanger is a common application where good thermal conductivity is important. Copper is a popular choice for heat exchangers in industrial facilities, air conditioning, refrigeration, hot water tanks and under-floor heating systems, its high thermal conductivity allows heat to pass through it quickly.
Testing the rate of heat conduction of a bar of metal. Place a lead solder or wax at the end of a bar of copper. Heat the bar at one end and record the time it takes for the solder or wax to start to melt. Repeat the experiment using other materials such as brass, aluminum and steel with the same diameter and length as the copper bar. Record in each case the time it takes to melt the lead solder or wax. Tabulate the result as shown below:
| Material | Time taken (minutes) |
| A | |
| B | |
| C | |
| D |
Using your result, arrange the materials from the best to the poorest heat conductors. Discuss the result with your teacher.
Sound Test
Metals produce different sounds when they are hit with a hammer. A bell made of brass will produce sound that is different from a bell made of iron. If you want to find out the rate of conductivity of different metals, the following experiment should be conducted.
Classes of Metals
Some metals are ferrous metals and others are non-ferrous metals contain no iron at all.
| Ferrous Metals | Non-Ferrous Metals |
| Wrought Iron | Brass |
| Cast Iron | Aluminum |
| Steel | Copper |
Forms of Metals
Metals also come in different forms. They could be round, rectangular, tubular, flat plates, strip, wires, etc.
Exercises
- Define the term metal
- List five forms of metal
- State the two general ways of classifying metals
- State four methods of identifying metals
- Which one of these conduct heat better – metals or non-metals
Answer
1. A metal is a material (an element, compound, or alloy) that is typically hard when in a solid state, opaque, shiny, and has a good electrical and thermal conductivity
2.Steel, copper, zinc, aluminum, and stainless steel
3. Ferrous and non-Ferrous metals. The ferrous metal has a measure of iron in them but non-ferrous metals contain no iron at all.
4. Density, Colour/Lustre, Fusibility, Magnetic effect
5. Metals
