TThe Earth contains about 90 different elements, substances that are not mixtures of anything else. More than 60 of these elements are metals, such as gold, copper, tin and iron. About 20 are nonmetals, while the remainder have properties that place them half-way between metals and nonmetals.
The First Use of Metals
People first used metals many thousands of years ago Before about 6000 BC the only tools and weapons were made of stone. While searching for suitable stones, people would have found pieces of pure metal, including gold, silver and copper. At first gold and silver were made into bracelets and
ornaments, while beaten copper made cooking pans and dishes as they were too soft for tools and weapons.
In Egypt in about 4000 BC people discovered how to smelt copper from copper ore. Later they learned that if you add tin the resulting alloy, bronze, was much tougher. The Bronze Age lasted from about 3500 BC to about 2000 BC, when iron smelting was invented in Anatolia. Iron swords, daggers, hoes and axes gradually replaced bronze.
Very few metals are found in the earth in the pure form we know. Gold is found by itself or embedded in other rocks, but iron has to be smelted out of rock. It is called iron ore.
Beautiful Metals
All over the world, and over many centuries, men have shaped metals into beautiful objects. Gold has always been a favourite because of its shiny yellow colour. It is also easy to beat into a shape. Also, gold does not decay or rust like some other metals.
Mixing Metals
The first metal to be found and worked upon was probably copper. But copper by itself was too soft, and people began mixing some tin with the copper. This made bronze, a metal that was much harder.
Most metals that we see every day are in fact mixtures. These mixtures are known as alloys. An alloy is often quite different from the metals that make it up.
There are hundreds of different alloys, and more are invented every year. The most common alloys are steels, which are made of iron with small amounts of carbon and other elements.
Pure Metals
Pure metals are solids at room temperature. The one exception is mercury, a heavy, silver-coloured metal which is liquid. Mercury is shiny, and so too are all other metals. Not all metals stay shiny when left in the air. Many, such as aluminium, lead and silver, eventually become dull and tarnished because elements such as oxygen in the air make new chemical compounds on the surface. Unless it is protected, iron goes rusty when exposed to air and water over time. The chemical name for rust is iron oxide because it is a combination of iron atoms and oxygen atoms. Metals, again with the exception of mercury, are strong. They can be bent without breaking. They are malleable - they can be hammered or rolled into different shapes. And they are ductile, which means that they can be pulled out to form wires. Metals are also good conductors of electricity and heat.
Joining Metals
Two ways of joining metals together are riveting and welding. In riveting, a metal plug with a rounded head goes through the holes in the parts to be joined. The other end is hammered until it also has a head which holds the pieces together.
Soldering is another way to join metals. An alloy, often a mixture of lead and tin, is melted between the two pieces of metal. When the solder cools it makes a firm joint. A paste called flux is put in to make a better joint.
Cutting Metals
Metals can be cut by using an oxyacetylene burner. This kind of burner makes a very hot flame by burning acetylene gas in oxygen.
Shaping Metals
There are many ways to shape metals. A simple way is casting. Molten metal is poured into a mould. The metal hardens in the shape of the mould. Pressing is used to shape sheets of steel. A heavy press forces the metal to the right shape. Forging has long been used by blacksmiths. The red-hot metal is shaped on an anvil. In rolling a white-hot piece of metal is squeezed between rollers until it is a thin sheet. In drawing thin rods are made by pulling metal through small holes.
The First Use of Metals
People first used metals many thousands of years ago Before about 6000 BC the only tools and weapons were made of stone. While searching for suitable stones, people would have found pieces of pure metal, including gold, silver and copper. At first gold and silver were made into bracelets and
ornaments, while beaten copper made cooking pans and dishes as they were too soft for tools and weapons.
In Egypt in about 4000 BC people discovered how to smelt copper from copper ore. Later they learned that if you add tin the resulting alloy, bronze, was much tougher. The Bronze Age lasted from about 3500 BC to about 2000 BC, when iron smelting was invented in Anatolia. Iron swords, daggers, hoes and axes gradually replaced bronze.
Very few metals are found in the earth in the pure form we know. Gold is found by itself or embedded in other rocks, but iron has to be smelted out of rock. It is called iron ore.
Beautiful Metals
All over the world, and over many centuries, men have shaped metals into beautiful objects. Gold has always been a favourite because of its shiny yellow colour. It is also easy to beat into a shape. Also, gold does not decay or rust like some other metals.
Mixing Metals
The first metal to be found and worked upon was probably copper. But copper by itself was too soft, and people began mixing some tin with the copper. This made bronze, a metal that was much harder.
Most metals that we see every day are in fact mixtures. These mixtures are known as alloys. An alloy is often quite different from the metals that make it up.
There are hundreds of different alloys, and more are invented every year. The most common alloys are steels, which are made of iron with small amounts of carbon and other elements.
Pure Metals
Pure metals are solids at room temperature. The one exception is mercury, a heavy, silver-coloured metal which is liquid. Mercury is shiny, and so too are all other metals. Not all metals stay shiny when left in the air. Many, such as aluminium, lead and silver, eventually become dull and tarnished because elements such as oxygen in the air make new chemical compounds on the surface. Unless it is protected, iron goes rusty when exposed to air and water over time. The chemical name for rust is iron oxide because it is a combination of iron atoms and oxygen atoms. Metals, again with the exception of mercury, are strong. They can be bent without breaking. They are malleable - they can be hammered or rolled into different shapes. And they are ductile, which means that they can be pulled out to form wires. Metals are also good conductors of electricity and heat.
Joining Metals
Two ways of joining metals together are riveting and welding. In riveting, a metal plug with a rounded head goes through the holes in the parts to be joined. The other end is hammered until it also has a head which holds the pieces together.
Soldering is another way to join metals. An alloy, often a mixture of lead and tin, is melted between the two pieces of metal. When the solder cools it makes a firm joint. A paste called flux is put in to make a better joint.
Cutting Metals
Metals can be cut by using an oxyacetylene burner. This kind of burner makes a very hot flame by burning acetylene gas in oxygen.
Shaping Metals
There are many ways to shape metals. A simple way is casting. Molten metal is poured into a mould. The metal hardens in the shape of the mould. Pressing is used to shape sheets of steel. A heavy press forces the metal to the right shape. Forging has long been used by blacksmiths. The red-hot metal is shaped on an anvil. In rolling a white-hot piece of metal is squeezed between rollers until it is a thin sheet. In drawing thin rods are made by pulling metal through small holes.
