Transcript Excellent VISUAL with What do Atoms Look Like

RADIOACTIVITY: ATOMIC STRUCTURE AND ISOTOPES
By the end of this presentation you should be
able to……
 Describe
the structure of the atom.
 Explain and recognise isotopes of an
element.
 Simply state the origin of radioactivity.
 Recall the properties of the three subatomic particles that make up an atom.
What do atoms look like?
They are very small!
Relative size of the atom and the
nucleus.
The ratio of the diameters is 10 000 : 1 !
If the diameter of a particular atom was
10 metres, its nucleus would be 1
millimetre across!!
Structure of the atom
nucleus
proton
neutron
electrons
The relative masses and charges of these particles
are given below
PARTICLE
MASS
CHARGE
Proton
1
+1
Neutron
1
0
Electron
1/ 2000
-1
Atoms of different elements are organised
based on their behaviour, which is very closely
related to the number of protons in their nuclei.
The periodic table shown in the previous slide does not
show the information provided in the usual way.
Usually each box looks like this….
(A) This is the “mass” or “nucleon number” and is equal to
the number of protons + the number of neutrons in the
nucleus.
14
N
7
NITROGEN
(Z) This is the “atomic” or “proton number” and is used
to identify the element.
BUT!
They then found two atoms of the same element (like
chlorine), that seemed to have different masses!
They both looked like chlorine, smelled like chlorine,
reacted in a similar way….so they must have the same
number of protons and electrons. They must be the
same element!
They solved the dilemma by calling these special
atoms “ISOTOPES”, and realised that the
difference in the mass must be caused by the
particle that contributes to mass, but is neutral, so
does not affect reactions!
ISOTOPES
Atoms that have the same number of protons (so
represent the same element) , but different
numbers of neutrons (so have different masses)
Hydrogen has isotopes.
Lithium has isotopes
In fact, many elements have isotopes
and some of them are….UNSTABLE!
This instability originates in the nucleus, and
in an attempt to become more stable, the
nucleus will literally “spit out” a particle or
some energy.
These unstable atoms are called “RADIOACTIVE”
The stuff that is spat out is called “RADIATION”
If the unstable atom is an isotope, it is called a
“RADIOISTOPE”.
RADIOACTIVITY: ATOMIC STRUCTURE AND ISOTOPES
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