Download Atoms HW 1/31 - Westerville City Schools

Atoms
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So if the atomic theory is just a theory, then how do we know atoms
exist? Better yet, how do we know that there are even different parts to
an atom? It seems like we know lots about something we have never
seen.
You are totally correct in being skeptical, but the evidence that Dalton,
Thomson, Rutherford, Bohr, and many other great scientists have
gathered has helped prove that atoms and their smaller parts do exist.
So even though we have never seen an atom, the evidence points to
atoms being there. For example, if you throw a baseball towards a friend
and it looks like it hits something in mid-air, your curiosity will suddenly
increase. You will keep throwing baseballs at the “invisible” something
trying to figure out what is there. Eventually, if you keep throwing
enough things at this “invisible” something from all different directions,
you will figure out the shape and size.
Atoms are very similar to this example. Scientists continue to throw, smash, break, and tear atoms apart to learn
about their size, shape, and structure. So have we seen an atom? No. Do we have a pretty good idea of what they
look like and what they are made of based on all of our experiments? Yes.
Introducing the Atom
So let’s formally introduce the building block of everything that is matter, the atom.
The atom is not very big. As a matter of fact, if we had a special ruler that measured
the diameter of an aluminum atom, we would find out that it would measure
0.00000003 cm. That’s 100 million times smaller than a bouncy ball!
Because they are so small, we can pack lots of them into a tiny space. Take a penny for
example. A penny contains 20,000,000,000,000,000,000,000 atoms – that’s 20 thousand billion billion atoms.
Think about the thickness of your hair. It’s over 300,000 atoms wide. We could go on and on. So, basically, there
are lots of atoms in our world.
So how does an atom compare to the other really small thing we have seen, the cell? For starters, a cell is a living
thing but atoms are not alive. Remember, cells are living things that can reproduce. Thanks to the Law of
Conservation of Mass (as well as physics), atoms cannot reproduce because the mass in our universe cannot be
created or destroyed.
As for size, atoms are much, much smaller than cells. To give you an idea of how small, one typical human cell
contains over 700 trillion atoms (that’s a 7 followed by 14 zeros)!
The Atomic Structure
Not long after the discovery of the atom, it was found that the atom is made up of two
different areas. The way this was discovered is the way that most things are learned about
really small particles. You smash them into other really small particles and watch what
happens (kind of a neat job if you like smashing stuff ).
Recall, Thomson had discovered that atoms contain tiny particles called "electrons," which
carry a negative electric charge. When his special light particles were around positive and negative charges, he
could bend the path of the particles. So Thomson knew that part of the atom had a negative charge.
As Rutherford found out, most of an atom is located in a very small spot at the center. This is what Rutherford
was trying to discover when he bombarded gold foil with a special type of light particle. Rutherford tried to figure
out how the special light particles were bouncing around and not passing straight through the atoms of gold foil,
and the best idea he could come up with was, in fact, the truth.
When the special light particle hit this tiny spot, it bounces back.
When it misses, it goes on through. From his experiments, he
was able to conclude that the atom has a small spot at the
center, which we now call the "nucleus," and it has a positive
charge.
So thanks to Rutherford and Thomson, the atom is found to be in
two parts: a tiny nucleus at the center, which contains a positive
charge we now call the proton, and the area around the nucleus,
which appears to have lots of empty space with negatively
charged electrons flying around inside it.
The Neutron
It took almost 20 years after Rutherford’s discovery though to figure out there was a third part of an atom. During
this time, many scientists believed that only the electron and proton existed.
By continuing to smash different atoms, scientists eventually discovered another particle inside the nucleus. This
particle has no electrical charge which is why it was so hard to find. This neutral charged particle is called the
neutron.
The Nucleus
Together, the proton and neutron make up almost all of the mass of an atom. They are both located in the
nucleus of an atom. Even though it has most of the mass, the nucleus makes up only a tiny part of the overall size.
The pictures we draw and see are not technically correct. If the nucleus was the size of our bouncy ball above, the
atom would be the size of Genoa Middle School.
What the nucleus lacks in size is made up for in mass. The weight of an atom comes mainly from protons and
neutrons. Protons and neutrons have similar weights coming in at 0.0000000000000000000000002 grams (that’s
a really small number). Because scientists did not want a periodic table with these really small numbers, they
came up with a new measurement called the atomic mass unit (amu). 1 amu is equal to the really small number
above. So when reading the periodic table, you can multiple the atomic mass by 0.0000000000000000000000002
grams to find out how much one atom of an element weighs in grams.
The Electron
As Thomson and Rutherford found, spinning in the vast emptiness of an atom is the negative charged particle, the
electron. Compared with the protons and neutrons, the electron is extremely light coming in almost 2000 times
lighter than a proton. For this reason, the mass of an atom listed on the periodic table ignores the weight of an
electron. So even though the electron takes up most of the space of an atom spinning around the outside of the
nucleus, the weight is often considered to be very close to zero.
The Elements
Currently, there are 118 known elements listed on the periodic table with 94 of them naturally occurring on Earth;
the remainder is made in a laboratory by scientists. Easily stated, the only major difference between each
element is the number of protons, electrons, and neutrons starting with the simplest element, Hydrogen, with
only 1 proton and 1 electron. As we add protons, electrons, and neutrons, the element changes.
As for everything you see and touch, all matter on earth is made up of at least one of these elements. Think of the
elements as our own alphabet. All the words, sentences, and books come from these same 26 letters just as all
matter comes from the 94 naturally occurring elements.
The Atom Guided Reading Questions
1. How did scientists discover the shape and size of atoms?
2. What are two differences between a cell and an atom?
a.
b.
3. Why did scientists have trouble discovering the neutron?
4. Use the reading to fill in the following chart:
Particle
Where is this particle located inside an
atom?
Proton
Electron
Neutron
5. How are the elements and alphabet similar?
What is the electrical
charge of this particle?
How much mass does the
particle have (in amu)?
6. Looking at your periodic table, fill in the blank for each element.
Element
Chemical
Symbol
Atomic
Number
Protons
Electrons
Atomic
Weight
Neutrons
Lithium
Beryllium
Phosphorus
Carbon
Oxygen
7. Compare the atomic number to the number of protons and electrons. What do you notice?
8. Find an element on the periodic table that sounds cool or different? What is it's chemical symbol? What is it's atomic
number?