Page 17 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Element
D
Decay
(See: Radioactive decay.) Dissolve
When a substance breaks down in a solution without creating a reaction. For example, salt dissolves in water and can be recovered by evaporating the water.
Doping
Adding an impurity to a semi- conductor to change its electrical conductivity.
Dubnium (Db)
Element 105 on the periodic table. An artificial radioactive element, also called unnilpentium (Unp), belonging to the transition metals.
It was made in 1967 at the Joint Institute for Nuclear Research in Dubna, Russia. It has no practical uses. Dubnium is a transuranium element.
Ductile
Capable of being drawn into a new shape like most metals.
(See also: Malleable.)
Dysprosium (Dy)
Element 66 on the periodic table. A rare-earth element and one of the lanthanides.
It is a relatively hard and very reactive metal with a high melting point. It was discovered in 1886 by Paul-Émile Lecoq de Boisbaudran. It readily absorbs neutrons and goes into control rods for nuclear reactors.
E
Einsteinium (Es)
Element 99 on the periodic table. An artificial and highly radioactive transuranium element in the actinide series.
It was discovered in 1952 by Albert Ghiorso. It was first identified from the debris of thermonuclear bomb tests. It is named for Albert Einstein.
Electron
A tiny, negatively charged particle that is part of an atom.
The flow of electrons through a solid material such as a copper wire produces an electric current.
 Ductile – Steel can be drawn out into sheets when hot or cold.
Element
A substance that cannot be decomposed into simpler substances by chemical means.
The ancient Greeks were the first to think that all substances were formed from fundamental particles. Their choice was air, earth, fire
and water. It took 2,000 years before it was realised that this idea was wrong and the modern understanding of elements began to develop.
The chemical elements have been discovered over thousands of years. Seven elements – gold, silver, copper, iron, lead, tin and mercury – have been known and used for thousands of years. They all occur as pure substances in nature. All others occur as compounds and so were not known until the age of scientific chemistry began in about 1600.
Sixteen elements were discovered in the 18th century and the others more recently.
It is thought that the first element to exist was hydrogen – the simplest of all, with one proton
and one electron. In the very early stages of the ‘Big Bang’ explosion that might have created the universe, hydrogen atoms fused to make helium, the second lightest element, with a nucleus of two protons and two neutrons.
The fusion of helium in stars produces elements as heavy as iron. Heavier elements can only be produced by fission.
Elements are identified by the way they absorb and emit light. Every atom takes in and puts out particular types (wavelengths) of light. A special machine called a spectroscope spreads out the light into coloured lines. Each element has its own pattern of coloured lines. In this way we can find out which elements make up a compound.
17