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Atoms
Atoms are composed of three types of
particles: protons, neutrons, and electrons.
Protons and neutrons are responsible for
most of the atomic mass in an atom. In other
words, for a person who weighs 150 pounds,
149 lbs, 15 oz are protons and neutrons while
only 1 oz. is electrons. The mass of an
electron is very small (9.108 X 10 -28 grams).
Atoms are so small:
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•
it would take a stack of about 50,000 aluminum atoms to equal
the thickness of a sheet of aluminum foil from your kitchen.
•
if you could enlarge a penny until it was as wide as the US, each
of its atoms would be only about 3 cm in diameter – about the
size of a ping-pong ball
•
a human hair is about 1 million carbon atoms wide.
•
a typical human cell contains roughly 1 trillion atoms.
•
a speck of dust might contain 3x10 12 (3 trillion) atoms.
•
it would take you around 500 years to count the number of atoms
in a grain of salt.
In order to try to gain an idea of how small an atom
really is, you will complete the following
activity.
Cut a strip of 11 in. paper in half.
Discard one half.
Cut the remaining piece in half.
Continue cutting and discarding the strips as many times as
you can.
5.
Make all cuts perpendicular to the first one.
6. Keep track of how many cuts you made.
1.
2.
3.
4.
 How many cuts were you able to make?
 Do you think you could keep cutting the paper
forever? Why or why not?
 You would have to cut the paper in half around
thirty-one (31) times to get to the size of any
atom!
 The atom is a basic unit of matter consisting of a
dense, central nucleus (where the protons and
neutrons are located) surrounded by an electron cloud
(where the electrons are located). It looks like this:
Both the protons and neutrons reside in the
nucleus.
Protons have a positive (+) charge.
Neutrons have no charge --they are neutral. Electrons
reside in orbitals, also called shells, around the
nucleus. They have a negative charge (-). Electrons are
in “orbitals” because they “orbit” the nucleus, much
like planets orbit their star.
Atoms make up all elements, the pure substances
that combine to make all the compounds, substances
and mixtures on earth. At present there are around
120 known elements, and they make up over 20
million substances.
There are 92 elements that occur naturally, charted on
the Periodic Table of Elements. The elements hydrogen,
carbon, nitrogen and oxygen are the elements that make
up most living organisms. Some other elements found in
living organisms are: magnesium, calcium, phosphorus,
sodium, potassium.
The other elements are created in the lab or during
nuclear fusion, the fusing of nuclei. These elements are
radioactive and break down over time, some quickly and
some over millions and billions of years. The elements
such as uranium, plutonium, and thorium are examples of
such elements.
The Periodic Table lists all known elements like hydrogen,
oxygen and gold. Hydrogen, the most abundant element in
the universe, makes up almost 90% of the total mass of
the universe. However, hydrogen atoms make up only about
1% of the Earth’s crust, and most of those hydrogen atoms
are combined with oxygen atoms in the form of water.
The living things on Earth are composed mostly of the
elements oxygen, carbon, nitrogen and hydrogen.
Atoms are the basic building blocks of matter. It is atoms
that make 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.
It cannot be broken down into smaller elements. All elements
are arranged into a table called the Periodic Table of
Elements.
Elements get their names in a variety of
ways. Some have been known for many years
and have Latin or English names. Magnesium
was named for a region in Greece called
magnesia. Lithium comes from the Latin word
“lithos” which means stone. Others have been
named after the scientist who discovered it
(einsteinium for Albert Einstein and fermium
for Enrico Fermi) or the place it was
discovered (berkelium, Berkeley.)
Each element has a unique symbol, based on its name.
For some elements, only the first letter of the name is
used such as oxygen (O), hydrogen (H) or nitrogen (N).
Others use the first letter plus one other letter of the
element’s name. The first letter is always capitalized
and any other letter is not. Aluminum (Al), Platinum (Pt)
and Cadmium (Cd) are some examples.
The origins of some elements are not as obvious as
others. Gold (Au) refers to the Latin name for gold,
aurum. Lead (Pb) comes from the Latin word plubnum
which means plumber. Copper (Cu) comes from the Latin
name cuprum which means copper.
•Each element has a certain number of particles, which
determines its atomic number and where it is located on
the Periodic Table.
•It is the number of protons that determines the
atomic number.
•For instance, hydrogen has one proton and one electron
so its atomic number is 1.
•The number of protons in an element is constant
(Hydrogen is always 1, Uranium is always 92) but the
neutron number may vary, so mass number (protons +
neutrons) may vary.
•Atomic number is determined by the number of protons,
and the atomic mass is determined by the addition of
the neutrons and the protons in the nucleus.
In an element that is not reactive, the number of electrons will be
the same as the number of protons. Remember that an electron is
negatively charged and a proton is positively charged. All the
negative particles have a matching positive particle.
The # of protons = # of electrons.
An isotope is an atom of an element that has a different
number of neutrons. Remember that neutrons help control the mass
of an atom. If an atom gains more neutrons, it becomes heavier. If
it loses neutrons, it becomes lighter.
Elements are made of atoms. Each element is made
of the same atoms. Change the type of atoms and
you change the element.
Atoms are composed of a nucleus, which has protons
and neutrons, and is surrounded by a dense cloud of
electrons. The protons, which are positively charged
and the neutrons, which have no charge, make up
most of the atom’s mass, approximately 99.9% of
the mass of an atom. The electrons are negatively
charged and move in orbits (also called shells or
levels) around the nucleus. They travel at 99.9999%
of the speed of light. To do this, they must weigh
almost nothing.
Vanadium has an atomic mass of 50.9415 (51), and 23
protons. How many neutrons?
Indium has a mass number of 114.818 (115), and 49
protons. How many neutrons?
Carbon has a mass number of 12.0107 (12) and 6 protons.
How many neutrons?
Vanadium has an atomic number of 50.9415 (51), and 23
protons. How many neutrons?
Answer: 28
Indium has a mass number of 114.818 (115), and 49
protons. How many neutrons?
Answer: 66
Carbon has a mass number of 12.0107 (12) and 6 protons.
How may neutrons?
Answer: 6
Atoms are extremely small. You can fit millions of atoms in the
period at the end of your sentence.
Each element is made up of millions of atoms since they make
substances and compounds that we interact with every day. The
identity of an atom is determined by information that is found on
the Periodic Table of Elements. You can find one in almost every
science room around the world.
Each element on the periodic table has information in its
box that tells us a lot of information about that
element.
Atomic number - an atom’s atomic number determines where it is
placed on the Periodic Table. That number tells us how many
protons an element has. Hydrogen (1) has 1 proton. Gold (79) has 79
protons. The number of protons an element has determines its
atomic number.
Atomic mass - the mass of an element can be determined by adding
the number of neutrons and protons an element has . Remember, the
nucleus has most of an atom’s mass? We find that number by adding
the two subatomic particles. An atom’s mass number is the largest
number in the element’s box on the Periodic Table.
Now that we are experts on the elements, let’s practice
on identifying the elements. Remember the box on the
Periodic Table has all the information we need to
identify an element.
The largest number is the atomic mass.
• The atomic mass is found by adding the protons and
the neutrons.
• The smallest number is the atomic number, which
equals the number of protons.
• The number of protons equals the number of
electrons, in a neutral element/atom.
•
1.
How many protons does helium have? Number of
electrons?
2.
What is the mass of silicon (Si)?
3.
What is the atomic number of sodium (Na)?
4.
Which element has only 7 protons?
5.
Which element has only 6 neutrons?
1. Helium has 2 protons (atomic number is 2), and 2
electrons (# of protons = # of electrons).
2. Silicon has an atomic mass of 28.086 amu.
3. Sodium (Na) has an atomic number of 11.
4. The element with only 7 protons is nitrogen (N).
5. The element with only 6 neutrons is carbon (mass is
12 amu minus 6 protons = 6 neutrons).