52
Atoms and molecules
Immortal atoms
the particles that make up atoms never
disappear but are constantly journeying
through the universe as part of different
substances. all these particles originated
with the formation of the universe around
13,700 million years ago. the atoms that
make everything on Earth were formed
from the particles in stars, which then
exploded like the Crab Nebula (above).ProtoNs aNd NEutroNs
the nucleus of an atom contains
particles called protons and neutrons.
these contain even smaller particles
called quarks. Protons carry electricity.
However, they carry a different kind of
electricity from electrons. they have a
“positive charge,” whereas electrons have
a “negative charge.” Neutrons have no
electric charge.A drop of water
contains about
1,000 million
billion
molecules.dNa
all plants and animals
contain molecules of dNa
(deoxyribonucleic acid).
dNa carries the blueprint
for life: coded information in
dNa molecules determines
the characteristics of each
living thing and its offspring.
a dNa molecule consists
of millions of atoms arranged
in a twisted spiral shape.look arouNd you. there are countless millions of different substances, from metals
and plastics to people and plants. all of these are made from about 100 different kinds of
“building blocks” joined together in different ways. these building blocks are tiny particles
called atoms. atoms are so small that even the tiniest speck of dust contains more than a
million billion atoms. some substances, such as iron, are made of just one kind of atom;
other substances, such as water, contain molecules—atoms joined together in
groups. such molecules may be very simple or very complex. Each water
molecule contains two hydrogen atoms and one oxygen atom; plastics
are made of molecules which often contain millions of atoms.
an atom itself is made up of a dense center called a nucleus.
Particles that carry electricity, called electrons, move
around the nucleus. scientists have discovered
how to split the nucleus, releasing enormous
energy which is used in nuclear power
stations and nuclear bombs.There is a lot of empty space in an
atom. If the nucleus were the size
of a tennis ball, the nearest
electron would be about
half a mile (1 km) away.Electrons whiz around the
nucleus. An atom of oxygen
has eight electrons.Discovering the atom
about 2,400 years ago, the Greek
philosopher democritus believed
that everything was made up of
tiny particles. It was not until
1808 that English scientist John
dalton proved that atoms exist.
around 1909, New Zealand
scientist Ernest rutherford
(below) discovered the nucleus.Find out more
Chemistry
oxygen
Physics
Plastics
reproductionA molecule of water
contains three atoms—
two hydrogen atoms
and one oxygen atom.Protons and
neutrons are made
up of quarks.The nucleus
of an oxygen
atom has eight
protons and
eight neutrons.
The nucleus is
held together by
powerful forces.US_052_Atoms_molecules.indd 52 20/01/16 4:33 pm