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B
Atoms
Atoms
Atomic symbols
Atoms
Atoms consist of a tiny
nucleus containing positivelycharged protons and neutral
neutrons, surrounded by a
cloud of negatively-charged
electrons.
Electrons are almost 2000
times smaller than protons
and neutrons, so almost all
the mass of an atom is
concentrated in its nucleus.
Although there are
only a few electrons,
they move so fast
they seem to occupy
the whole volume of
the atom.
Atomic symbols
Mass number
Scientists summarise the
most important data about an Atomic number
atom by listing its atomic
number and its mass number.
11
5
The atomic number is equal to
the numbers of protons.
The mass number give the
total number of massive
particles: the protons and
neutrons.
This atom has:
This diagram shows that the
electrons are found in shells.
11 – 5 = 6 neutrons
5 protons
5 electrons
Inside atoms
The nucleus, in the centre of an atom, contains protons
and neutrons, while the electrons orbit the nucleus in
shells.
Particle
Proton
Neutron
Mass
1
1
Charge
+1
0
Nucleus
Electron
1
1836
–1
Shells
The atomic number is the number
of protons in an atom.
The mass number is the number of
protons plus neutrons.
3B 1 Atom words
Position
Nucleus
Isotopes
Isotopes are atoms with the
same number of protons but
different numbers of neutrons.
Isotopes have the same atomic number but different
mass numbers.
They have the same chemical properties because they
have the same electron structure. However, because
isotopes have slightly different masses some of their
physical properties are different.
3B 2 How chemists changed the NZ wine industry
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