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ELEMENTS

The enormous variety of matter around you is made from different combinations of substances called elements. Elements are pure substances that cannot be broken down into anything simpler. Some, such as gold and silver, are found on their own. Most elements, however, are combined in twos, threes, and more to make compounds. The NATURAL ELEMENTS are found on Earth. SYNTHETIC ELEMENTS are created in laboratories and are often short-lived.

METEORITE

An element is always the same, wherever it is found. For example, meteorites are large rocks that have landed on Earth from space. Some meteorites contain metal, such as iron, which is a natural element. The iron in a meteorite from space is exactly the same as iron found in rocks on Earth.

ORIGIN OF ELEMENTS

All the elements on Earth were formed in the heart of exploding stars. The early Universe was made of just two elements, hydrogen and helium, which formed into stars. At the fiery core of these stars, the hydrogen and helium were forced together to form new, heavier elements. Even heavier elements were created in the explosions of massive stars, called supernovas.

Table 2. ELEMENTS IN THE EARTH'S CRUST

ELEMENTPERCENTAGE
Oxygen47
Silicon28
Aluminium8
Iron5
Calcium3.5
Sodium3
Potassium2.5
Magnesium2
All other elements1

BIOGRAPHY: JOHN DALTON English, 1766–1844

Chemist John Dalton studied the gases in air. He proposed that everything was made from simple substances called elements. He said that the properties (characteristics) of every particle of one element are identical, and are different to the properties of any other element. This is how elements are defined today.

NATURAL ELEMENTS

There are 90 natural elements, ranging from the lightest, hydrogen, to the heaviest, uranium. Other familiar elements are aluminium, carbon, copper, and oxygen. Every substance on Earth is made up of one or more of these 90 elements. Oxygen is the most common element on Earth. Hydrogen is the most common element in the Universe.

ALUMINIUM

Aluminium is a common element, but it is never found naturally on its own. It has to be extracted from rocks called minerals. This extraction process used to be very difficult and aluminium was once considered a precious metal, more valuable than gold. Nowadays, extraction is much easier, and aluminium is used for many everyday items, such as drinks cans and foil.

SYNTHETIC ELEMENTS

No element heavier than uranium is found naturally. Scientists can, however, collide two smaller elements together at high speeds to form a new, heavier element. Many elements made this way break apart almost immediately, although a few can stay together for a few days or even weeks. Scientists make them to learn more about how elements form and how they change as they get heavier. Synthetic elements include plutonium and einsteinium.

CYCLOTRON

Scientists create synthetic elements in a cyclotron. The cyclotron contains a circular track, into which particles are released. The particles are speeded up to extremely high speeds, before being allowed to collide with a target of another element to form new elements. In the largest cyclotrons, the ring is many kilometres wide and the particles speed at 225,000 kph (13,809 mph).

Copyright © 2007 Dorling Kindersley

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