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Hi guys! So this is the presentation about atomic structure that we had in class on Monday.
The first thing you want to talk about when you think about atomic structure is "What
is an atom?" Now we've talked about matter in class over the last week and a half or
so and an atom is simply the basic unit of all forms of matter. So anything that's considered
matter has atoms and anything that is not matter does not have atoms. Now what we know
about atoms is based on an atomic theory that was invented by a scientists named John Dalton
in the 1800s and there are 3 parts to that theory. The first is that everything is made
of atoms. The second is that all atoms of a specific element are the same. And the third
is that atoms cannot be created or destroyed. Now the way you can look at this atomic theory
is by rephrasing some of those pieces so if you look at the first part every-THING is
made of atoms. Anything that does not have atoms does not count as a thing. And that
all elements of a specific element are the same...if you rephrase that all elements of
a specific type are going to be the same. We'll look into this a lot more during our
periodic table unit. The third section, atoms cannot be created or destroyed, we've already
discussed several times during the properties unit when we've talked about how you can't
get something from nothing and you cannot get nothing from something. Now atoms are
made of 3 particles that are concentrated in 2 areas. Now on the right side of the screen
you can see those 2 areas--the first is the nucleus and this is at the very center of
an atom. This area is extremely dense and contains the majority of the mass of an atom.
Around the nucleus are the electron shells. Sometimes these shells are also called "orbitals."
These are going to be extremely far away from the nucleus and they're responsible for how
an atom is able to bond with other atoms to form all the substances of our planet. Now
inside the nucleus and the electron shells are 3 particles. The first of these is a proton.
Protons have positive charge and they are inside the nucleus. The second particle is
called a neutron and they have what we call a neutral, or zero, charge and these are also
in the nucleus. On the outside of the atom in those electron shells or orbitals are the
electrons. These have a negative charge. Now when you're trying to decide what things are
in an atom and how many things are in an atom you have to start using the different characteristics
of an atom that are documented in the Periodic Table to find that information out. So on
the Periodic Table you're going to have an atomic number. Now the atomic number can tell
you the number of protons or the number of electrons. For example, all hydrogen atoms
have 1 proton. This goes back to that second part of the atomic theory that says all atoms
of a specific element are the same. So anything that is an atom, in order for it to be considered
hydrogen can only have 1 proton. And another example would be carbon which has 6 protons
and all carbon atoms will have 6 protons. To find the number of neutrons you have to
use the atomic mass which is also found on the Periodic Table. The atomic mass is equal
to the number of protons and the number of neutrons. Now to find the number of neutrons
you take the atomic mass subtract the number of protons and that will give you the number
of neutrons. Please note that the atomic mass is also sometimes called the mass number is
some textbooks and readings we'll be using, but the atomic mass and mass number are the
exact same thing. Now even though you can count the parts of an atom when you change
the number of protons, neutrons, or electrons you are completely altering the chemical or
physical properties that atom will display. For example, changing the number of protons
produced an extremely dramatic effect because all atoms of the same element have the same
number of protons. For example, all helium atoms will have 2 protons and all sodium atoms,
or sorry, nitrogen atoms will have 7 protons. Please forgive my typo. When you change the
number of protons you are completely changing the atoms identity. So, if you take a helium
atom and you add a proton to it, you have changed the helium atom to a lithium atom.
If you take an oxygen atom and subtract a proton from it you then end up with a nitrogen
atom. Changing the number of neutrons produces a somewhat less dramatic effect, but it can
be very chemically interesting. Now all atoms of an element have the same number of protons
like I said before, but the number of neutrons in an atom doesn't need to match the number
of neutrons. For instance, all chlorine atoms will have 17 protons, but some of these chlorine
atoms have 18 neutrons while others have 20. When an atom has a different number of neutrons
you call it an isotope. Now some elements are going to have many, many, many neutrons
and others only have a few. The way you talk about isotopes is by taking their name and
adding their atomic mass on the back. So, if you're talking about chlorine that has
18 neutrons you're talking about Chlorine-35. Chlorine with 20 neutrons is called chlorine-37.
When you change the number of electrons you completely alter your atom's ability to bond
with another substance. Now most atoms have no electrical charge, or a neutral charge,
because the number of protons is equal to the number of electrons. When an atom looses
or gains an electron it becomes what's called an ion. Now there are 2 kinds of ions. There's
a positive ion which means your atom has more protons than electrons and a negative ion
which means your atom has fewer protons than electrons. Now a nitrogen atom with 7 protons
and 4 electrons is going to have a charge of +3 because in that nitrogen atom you have
7 protons (so, 7 positive charges) and 4 electrons (which means 4 negative charges). So +7-4=+3.
A magnesium atom with 12 protons and 15 electrons is going to have a charge of -3 because 12
positive charges minus 15 negative charges equals -3.