ELEMENTS OF LIFE
EL1
What Are We Made Of?
Elements
and the body.
A mixture
of chemicals makes up the human body that are called compounds,
which are made of elements.
o
Define
the terms in bold type.
The
elements are further classified into 3 main groups:
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Counting
atoms of elements
Study
table 1.
o
Why
is studying the mass of elements an inaccurate way of determining the quantities of
elements in the body?
o
What
is the best way to determine the amount of an element in the body?
The
chemist uses a system called THE MOLE to
enable them to determine an exact number of atoms of an element there may be in
a chemical, even though they are impossibly small to count.
EL2
Take 2 Elements…
A
trace is all you need
There
are many important trace elements in the body.
o
See
table 3.
An
Iron Story.
Iron is
present in the molecule haemoglobin.
o
What
is its role?
o
How
does it do its job?
A
Calcium Story.
o
What
is the role of calcium in the body?
o
What
are the problems that can arise should there be a deficiency?
o
How
are these deficiencies discovered and what techniques are used?
As more
and more elements were being discovered and more was being learnt about the
elements already known, chemists decided to organise them into a table.
Some
elements are closely related to each other in terms of their behaviour. They are
placed into ‘families’ or groups.
By
1850, 59 out of the 92 elements now known had been discovered. Dobereiner,
Meyer, Newlands and Mendeleev all searched for patterns in the
elements and tried to arrange them in a table.
See
fig.7
Read
pg.8.
The
modern Periodic Table is based on the work of Mendeleev.
A
star is born.
Hydrogen
is the most common elements in the Universe. It forms the basis of the theory of
how stars are formed and hence the planets in solar systems.
In
space hydrogen atoms are very spaced apart. This is why they exist in the form
of atoms, as it is so unlikely that they will collide and form H2
molecules. In some parts of space, molecular gas clouds can form, made form a
mixture of H atoms and ‘dust’. The temperatures are low, 10-100K and so they
move slowly, with little kinetic energy. Gravitational forces keep them
together. The cloud gradually contracts and the gas cloud compresses until
‘clumps’ of denser gas forms. At the centre, the temperatures become so
large, due to compression, that nuclear reactions take place to form a star.
Nuclear reactions generate a hot wind that drives away some of the dust and gas,
leaving a star behind, doing nuclear reactions with hydrogen. This dust then
goes on to form planets around the star, thus creating a solar system.
q
What is a
nuclear reaction?
q
What is
nuclear fusion?
q
Give two
examples of nuclear reactions that take place in these gas clumps.
q
Why does
this cause the gas cloud to glow?
Heavyweight
stars.
All
stars convert H into He by nuclear fusion reactions.
In
heavier stars, the temperatures are higher at the centre of the star. The rates
of these reactions are therefore higher here. The temperatures and pressures get
so high, that the He atoms continue to do fusion reactions with each other and
make other elements.
This
causes layers of elements to form around the centre of the star, with the
heaviest forming in the centre where it is hottest.
After a
few million years, after extensive fusion, the element in the centre is Fe.
At this point, instead of releasing energy in their reactions, the reactions
begin to absorb energy until the star becomes explosive. When a heavyweight
star explodes, a supernova is formed. The elements that have formed are
dispersed and become gas clouds again.
The
Sun – A lightweight among stars.
The Sun
is referred to as a lightweight star
– it is not as hot as heavyweight stars and will last longer. Once the
hydrogen is used up it will expand into a red
giant.
q
What
will happen when the sun becomes a red giant?
q
When
will this happen?
q
What
is a white dwarf?
How
do we know so much about outer space?
Important
discoveries have been made about space using a technique called spectroscopy.
q
What
is spectroscopy?
We can
analyse the electromagnetic radiation absorbed or emitted by a substance, it can
reveal information about its structure.
Absorption
Spectra
All
stars emit e.m. radiation. (IR, Vis., UV)
The
photosphere is 6000K and emits visible light of all λ.
The
chromosphere contains ions, atoms and possibly small molecules.
All of
these particles absorb specific frequencies
of radiation and give an absorption
spectrum. These have a light background with black lines where
absorption has occurred. Each black line is the absence of a particular
frequency of radiation.
Each
element has its own characteristic absorption pattern.
Emission
Spectra.
When
atoms/molecules absorb radiation, (a form of energy) they become excited
.they move to a higher energy state.
They
then lose this energy and return to a ‘normal’ ground
state by emitting this radiation.
This
results in an emission
spectrum. These have a black background with light stripes to show the
radiation that has been emitted. Only during an eclipse can the emission spectra
for H and He be detected.
Our
Solar System
It is
formed form a huge gas cloud originating from a supernova.
Rings
of gas and dust condensed to form planets.
Denser
elements condensed near to the sun to form small rocky planets and the lighter
elements condensed further away to produce giant ‘fluid’ planets
Other
elements formed as a result of radioactive decay to for the other elements.
Atoms
make up molecules.
Molecules
make up all life forms.
In the
colder parts of the universe, the individual atoms collide and form bonds with
each other, thus making molecules. These have been detected in the gas clouds.
See
table 5.
The
molecules in the table are organic.
The elements found here are also the elements found in the human body. This is
no coincidence.
Where
did the molecules of life come from?
Some
scientists believe that the molecules in the dense gas clouds were the building
blocks that make up life on earth.
Read
about the experiments of Stanley Miller.
Read
this and prepare for the test on elements of life.