Metals
What are metals?
Metals are usually described as an arrangement of positive ions surrounded by a sea of delocalized electrons. They are distinguished on the periodic table by their ionization and bonding properties.
Chemical Properties.
Metals form cations when they lose electrons and they react with the oxygen in the air to form oxides over time.
4Na + O2 → 2Na2O (sodium oxide)
2Ca + O2 → 2CaO (calcium oxide)
4Al + 3O2 → 2Al2O3 (aluminum oxide)
The oxides of metals are usually basic as compared to the oxides of non-metals which are acidic.
Physical properties.
Most metals in general have high electric and thermal conductivity. They also have high densities. There are several metals that have low densities and low melting points. They are called alkaline earth metals. Planes of atoms in a metal are able to slide over one another under stress, proving the ability of a crystal to form without shattering.
Alloys
An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable colour.
Making the alloy
• Weigh out 1 g each of lead and tin. Put the lead into the crucible, but keep the tin to one side.
• If using casting sand, fill one of the sand trays with casting and push your finger into it to make an indent. This is your cast.
• Put the crucible onto a pipe clay triangle. Make sure that it is stable on a tripod and mat.
• Heat the crucible strongly with a Bunsen burner until the lead is molten. Add a spatula of carbon powder to the top of it to prevent a skin forming.
• Add the tin and stir with a spatula until the metals are both molten and thoroughly mixed.
• Move the Bunsen away from the tripod and put it onto a yellow flame. Wearing thermal protection gloves, pick up the crucible using the tongs, and pour the molten metal into the cast or onto a ceramic tile. Take great care as you do this to avoid splashing or dripping.
• Let it cool down completely before you touch it.
Testing the alloy
• Hardness testing Try to scratch the alloy with the lead, and the lead with the alloy. The one which does not scratch is the hardest.
• Density testing Hold the lead in one hand and the alloy in the other. Which seems to be the heaviest/most dense?
• Melting-point testing Put the alloy, a piece of tin and a piece of lead onto a sand tray. They should all be the same distance from the middle of the dish. Heat the dish gently in the middle. When two of the metals have melted, stop heating.
