Download cOO The.Parts of the Atom J

The Parts of the Atom
Learning About Atoms
cOO The.Parts of the Atom
J
T h e r e are three basic parts of the a t o m : proton, neutron, and electron. T h e protons
and neutrons are located in the center of the a t o m ; this area is called the n u c l e u s . T h e electrons are found orbiting around the nucleus in an area w e call the electron c l o u d . They are
organized into levels within the electron cloud, and the outermost level is referred to as the
v a l e n c e e n e r g y level.
To understand the relative size of the atom, it is necessary to visualize something we
already know something about. If the nucleus of the atom were about the size of a racket ball, the
atom would have a diameter of more than 2 k m . Another way to visualize the atom is to imagine
that the nucleus is an ant crawling around at the centerline of a football field, and the first group
of electrons would be circling 55 yards away (the end zones). Think of the distance between the
ant and the end zones as empty space within the atom. Now shrink your relative thinking to the
very, very small size of the atom. It now b e c o m e s much easier to think of the atom as really not
m u c h more than empty space. T h e actual atom is more than 9 9 % empty space.
Let's take an in-depth look at each of these particles, the three basic parts of the atom:
proton, neutron, and e l e c t r o n .
Particle
Charge
Location
Weight
proton
positive (+)
nucleus
1 amu
neutron
neutral (no charge)
nucleus
1 amu
electron
negative (-)
electron cloud
0.0018 a m u
a m u = atomic mass unit
If we w e r e to look at a two-dimensional model of the a t o m , it might look like the following:
Notice the placement of the protons and neutrons
together in the center of the drawing. This represents the nucleus.
T h e electrons will spin or orbit around the nucleus
in a space called the electron cloud.There are many
levels within the electron cloud.
T h e first level can hold up to 2 electrons and the
s e c o n d level can hold up to 8 electrons. T h e first
level must be filled before beginning to fill the second level.
©MarkTwain Media, Inc., Publishers
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Learning About Atoms
The Parts of the Atom: Reinforcement Activity
Name:
Date:
The Parts of the Atom: Reinforcement
Activity
To the s t u d e n t o b s e r v e r : W h a t are the parts of the atom?
A n a l y z e : W h y do scientists use models of the atom w h e n w e know that they are not completely
accurate?
D i r e c t i o n s : Answer the following questions about the a t o m .
1.
T h e atom can be divided into
basic parts.
2.
T h e three particles of the a t o m are the
,
and
3.
T h e protons a n d neutrons are located in the
4.
T h e electrons are found in the
5.
T h e electrons spin a r o u n d or
6.
T h e nucleus contains w h i c h atomic particles?
7.
T h e electron cloud contains which atomic particles?
the nucleus.
and
W h a t are the charges of the particles?
8.
protons
9.
neutrons
10.
Look at the two-dimensional model of the a t o m . H o w
m a n y of each of the following do you find?
11.
protons
12.
neutrons
13.
electrons
14.
W h a t is the weight of the nucleus of this atom?
15.
An atom is v e r y very small. If y o u were to look at
one atom through a microscope, what w o u l d take
up most of the viewing area?
© Mark Twain Media, Inc., Publishers
8
electrons
Everything You Wanted to Know About Isotopes!
Learning About Atoms
Name:
Date:
Isotope is very m u c h a science-specific vocabulary w o r d , and it m e a n s that an atom has
extra neutrons or is missing s o m e of its neutrons. This is not to be confused with ions, which are
a t o m s missing or having extra electrons. Since the number of protons an atom contains determines the a t o m , neutron n u m b e r s can c h a n g e , but the atom is still the s a m e . Let's take a closer
look at carbon and see if this makes sense.
Carbon is carbon b e c a u s e it has six protons. If the atom had seven protons, it would be
nitrogen, a n d five protons w o u l d make the a t o m boron. Since carbon has six protons, w e know
that it also has six electrons (before it bonds). However, carbon a t o m s can be found with different n u m b e r s of neutrons. A s you know, all living objects contain c a r b o n , so carbon is found all
over the universe. If the carbon c o m e s from burning an oak tree in Illinois, w e could analyze the
carbon and find that it is m a d e of six protons and six neutrons. This is n a m e d Carbon-12. T h e
12, as you can guess, is found by adding the number of protons a n d neutrons found in the
nucleus of the a t o m . If we found s o m e carbon from a rotting, decayed, and unidentifiable road
kill in New Mexico and analyzed it, w e might find that the carbon a t o m s all have six protons and
eight neutrons. This w o u l d be C a r b o n - 1 4 . By referring to it as Carbon-12 or Carbon-14, you are
telling the mass number of the c a r b o n . T h e m a s s n u m b e r is the s u m of the protons and neutrons of the atom.
Let's go back to our original topic and review the t e r m isotope. Carbon-12 and Carbon14 are isotopes of carbon. It is true that these atoms are a little different, by two neutrons, but
they are still carbon because they both still have six protons!
mass number
atomic number
•
1
H
1
?H
?H
Here are three isotopes of hydrogen. Each atom of hydrogen has one proton in its nucleus,
so t h e atomic number of each is " 1 . " A s you can see, the atomic number is the " 1 " listed to the
bottom left of each "H." T h e m a s s n u m b e r (the s u m of the protons and neutrons) of each of
these atoms varies due to the differing number of n e u t r o n s . T h e first isotope has one proton and
zero neutrons. T h e s e c o n d has one proton and one neutron. T h e third isotope of hydrogen
contains one proton and two neutrons in the nucleus, for a total m a s s number of 3. T h e picture
on the next page represents the three isotopes of hydrogen. T h e s e isotopes are so well known
and used so often that scientists have n a m e d the isotopes of hydrogen.
© Mark Twain Media, Inc., Publishers
24
Learning About Atoms
Everything You Wanted to Know About Isotopes!
Name:
Date:
Everything You Wanted to Know About
Isotope
Hydrogen (H)
Deuterium (D)
Tritium (T)
Isotopes s e e m to have a mind of their own and can't s e e m to follow any rules. So, of
course, there are no set number of isotopes any one element can have. The best "balance" of
protons and neutrons s e e m s to do a better job of holding the nucleus together. There is a trend,
however—light elements tend to have about as many neutrons as protons, and heavy elements
tend to have more neutrons than protons. A t o m s with too few or too many neutrons tend to be
unstable. T h e s e atoms are radioactive. Their nuclei change or decay by giving off radiation in the
form of particles or electromagnetic waves. (FYI: Radiation is energy that moves through space
as wave particles, while radioactivity is the property of spontaneous release of radiation.)
Lastly, w e need to understand the difference between m a s s number and atomic mass.
W e learned that mass number simply refers to the s u m of the protons and neutrons. W e use the
mass number to identify the isotope. For example, chlorine has 17 protons, and one isotope of
chlorine has 18 neutrons, while another c o m m o n isotope has 2 0 neutrons. If w e say chlorine35, w e are referring to the isotope with 18 neutrons (17 protons + 18 neutrons = 35 mass
number).
Now let's take a look at the t e r m a t o m i c m a s s . If you look at a periodic table, y o u will
notice that the atomic mass of an element is s e l d o m a whole number. Here is an example of
chlorine. T h e atomic m a s s is the average mass of an atom of an element. The atomic mass unit
(amu) is defined as 1/12 the m a s s of a Carbon-12 a t o m . W h e n atomic m a s s
17
2
is calculated, all of the different isotopes of an atom are taken into account.
8
If w e take a closer look at chlorine, the atomic mass is 35.453. Basically,
7
7 5 % of all chlorine is found as Chlorine-35, and 2 5 % is Chlorine-37. If y o u
CI
take the average b a s e d on their mass numbers and percentage found, the
Chlorine
atomic mass of chlorine is 35.453.
35.453
©MarkTwain Media, Inc., Publishers
25
Name
Date
Activity 19: C a l c u l a t i n g P r o t o n s , Neutrons,
Electrons Given A a n d Z
and
Directions: Complete the table. Assume that the atoms are neutral when calculating electrons.
ELEMENT
ELEMENT
SYMBOL
Carbon
Silicon
ATOMIC
NUMBER
(Z)
MASS
NUMBER
(A)
NUMBER
OF
PROTONS
6
Fe
26
28
56
14
79
Fluorine
Oxygen
82
8
Mg
K
Copper
Nitrogen
Hydrogen
19
16
19
47
12
20
64
14
1
29
Na
©1985, 2000 J. Weston Walch, Publisher
118
61
125
9
12
7
1
NUMBER
OF
ELECTRONS
6
Gold
Ag
Pb
NUMBER
OF
NEUTRONS
11
34
12
(D
Mastering the Periodic Table