Download Level 1- Recap, The Atom

Level 1- Recap, The Atom
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Proton
N
Neutron
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Electron
The Bits
Protons and Neutrons are in the nucleus. Electrons are in orbit outside the nucleus.
The electrons are arranged in
shells around the nucleus
Each shell can contain only a fixed number of electrons: The 1st shell can hold up
to two electrons, the 2nd shell can hold up to eight electrons, the 3rd shell can
hold up to 18, and 4th shell can hold up to 32 and so on. Since electrons are
electrically attracted to the nucleus, an atom's electrons will generally occupy
outer shells only if the more inner shells have already been completely filled by
other electrons (usually).
The electrons in the outermost occupied shell (or shells) determine the chemical
properties of the atom; it is called the valence shell.
Elements
A chemical element is a pure chemical
substance consisting of one type of atom
distinguished by its atomic number, which is the
number of protons in its nucleus.
Periodic Table of Elements
Simplified, showing stable elements. Notice how in each case there is the same number
of protons(+) and electrons(-). The overall electrical charge is ZERO. Keep that in mind
for later!
The complete table
Don't get stressed. At this stage you only need to know that elements are divided into groups
This simplified table shows only
the number of protons in each
element
It tells you how the table is, roughly, organised. It's actually a lot more complicated. You will
Learn about that in year 11 and 12.
Isotopes
Isotopes are variants of a particular chemical element such that, while all isotopes of a given element share the same
number of protons and electrons, each isotope differs from the others in its number of neutrons.
For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14
respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers
of these isotopes are 6, 7 and 8 respectively.
About atomic weight
Look at the atomic weights of a few different elements
on your periodic table. Do you notice that very few of
the elements have atomic weights that are close to
being nice whole numbers?
Do you know why this is? After all, for our purposes,
the mass of both the proton and the neutron are almost
exactly 1, and in chemistry we usually ignore the mass
of the electron because it is so very small.
Why then, if the mass of the atom comes mainly from
the protons and neutrons it contains, don’t the atomic
weights of the all come out to be nice whole numbers?
The reason is this; the atomic weights given on your
tables are “weighted averages” of the weights of the
different naturally occurring isotopes of the element.
Let’s look at an example.
Approximately 75% of the chlorine atoms found in
nature have a mass of 35. The other 25% have a mass
of 37. What should we report as the atomic weight for
chlorine?
What we do is to take the “weighted average” of these
isotopes. We multiply 75% times 35 and then add that
to 25% times 37...
[(.75)(35)] + [(.25)(37)]
= 26.25 + 9.25
= 35.5
Level 2, Molecules
A molecule is an electrically neutral group of two
or more atoms held together by bonds formed in
the sharing of electrons
Shell Love
In nature, usually atoms don't like to have vacancies in their shells, so most of the time
they will try to fill these spaces by pairing up.
The single atoms will attempt to bond and form a molecule. There are a number of different
types of bonds.
Different types of bonds
Covalent bonds
Ionic bonds
Metallic bonds
Different groups of elements bond in different ways. What they are all trying to do is to
arrange themselves in to some type of stable structure. It's all about the
electrical charges between the nucleus and the electrons in the shells.
Covalent Chemical Bonds.
In the simplest view of a so-called 'covalent' bond, one or more electrons (often a pair
of electrons) are drawn into the space between the two atomic nuclei. Here the
negatively charged electrons are attracted to the positive charges of both nuclei,
instead of just their own.
The oxygen atom has space in it's outer shell for two more electrons. The hydrogen atom
has space in it's single shell for one more electrons. By sharing electrons each atom fills
up the spaces in it's shell.
Ionic Bonds
In a simplified view of an ionic bond, the bonding electron is not shared at all, but
transferred. In this type of bond, the outer atomic orbital of one atom has a vacancy
which allows addition of one or more electrons.
This transfer causes one atom to assume a net positive charge, and the other to
assume a net negative charge. The bond then results from electrostatic attraction
between atoms, and the atoms become positive or negatively charged ions.
A quick note about Ions
An ion is an atom or molecule in which the total number of electrons is not equal to the
total number of protons, giving the atom a net positive or negative electrical charge.
Ions love to bond and get stable (have a net neutral charge). They are very reactive.
Metallic Bonds
A less often mentioned type of bonding is the metallic bond. In this type of bonding,
each atom in a metal donates one or more electrons to a "sea" of electrons that reside
between many metal atoms.
Metals are just party animals. The electrons are jumping into and out of the shells of
each atom. Bit like a big car park. While they are parked they stabilise the nucleus.
When they move out another one jumps in.
Because there are free electrons whizzing around they can be made to move.
Electricity is just moving electrons in a metal. But that's another topic.
But how can we know this!
We have the photos
Chemical bonds and molecular structure have
proven experimentally accurate in organic
chemistry research labs all over the world, but
few suspected the models would look so close
to reality. A team of researchers from The
Department of Energy’s Berkeley Lab have
acquired images of bonds breaking and
forming during a chemical reaction, and the
real molecules look like they’re copied out of
the textbook diagrams.
The images published in Science show
several molecules, starting with oligo(phenylene-1,2-ethynylenes), which is a
cluster of three benzene rings linked with
carbon chains. Placed next to the skeletal
diagram, it’s a stunningly good match. After
initiating a temperature-dependant organic
reaction, the experiment was imaged again.
The reaction products were present, and they
too looked exactly as predicted by the models.