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3
Answer the following questions.
a
What is an atom?
b
Name the three types of particles in an atom.
c
How many naturally occurring elements are there in nature?
d
When is a material said to be pure?
e
What is a chemical bond?
f
How many types of chemical bonds are there?
g
What states can a substance have?
4
Draw an atom with its protons neutrons and electrons.
The origins of materials
T
here is an infinite number of materials
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, often very different from one another. One important task for
engineers is selecting the most suitable materials for the components they are working on. This selection is
made on the basis of various factors: the properties, the mass, any climatic, chemical and machining requirements,
etc. of the material itself.
All materials are derived from elements. About 90 elements occur naturally on Earth.
A material that consists of only one element is said to be pure. Many materials are formed by mixing different
types of elements: for example the metal
brass
is an alloy, i.e. a mixture of two other metals,
copper
and
zinc
.
An atom is the smallest part of an element that still retains
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the characteristics of the element. Atoms are very
small and are made up of three types of particles:
protons, neutrons and electrons.
Protons and neutrons form the nucleus – the
central core – and electrons move around this
nucleus. Protons carry positive electrical charges,
electrons carry negative charges.
In most cases, atoms will join together to form
molecules. Oxygen, for example, is a molecule,
which is formed by two oxygen atoms joining
together. Molecules can also be formed by different
types of atoms joining together. For example
a water molecule is the result of two atoms of
hydrogen joining with one atom of oxygen.
Atoms adhere to form molecules by means of
chemical bonds. These
chemical bonds
can
be primary (very strong) or secondary (weak).
There are three primary bonds: metallic, ionic and
covalent
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.
Substances
are usually classified according to
the state they are at normal
room temperature
and pressure. The state can be gas, liquid or solid.
The state of a substance is the result of its chemical bonds and its temperature.
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materials
: the substances or components that products are made from
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retains
: still has, still keeps/maintains
3
covalent
: chemical bonds formed by the sharing of electrons between atoms (definition: Merriam Webster)
TEXT 1
The periodic table of the elements.
brass
ottone
chemical bond
legame chimico
copper
rame
room temperature
temperatura ambiente
substance
sostanza
zinc
zinco
TECHNICAL ENGLISH
Progetto FOR MECHANICALS_unit_1.indd 17
24/01/