Transcript Atom Drawing INSTRUCTIONS DRB

Daniel R. Barnes
Init:10/2/09
. . . draw an atom when given a chemical symbol
with a mass number and an electric charge.
“SWBAT = “Students will be able to”
There are many ways to draw atoms, but in this
class, you’re going to learn the Mr. Barnes method.
It’s not the only good way to draw atoms. In fact, as
you probably already know, it’s unrealistic in many
ways, but it’s useful for learning purposes.
So here we go. If you haven’t already got paper and
something to write with, get’em out, because you’re
going to need to TAKE NOTES on the process.
You’re also going to need use the periodic table side
of your CST Reference Sheet. If you’re at home
right now and don’t have one, click the red button
and the pdf will pop up. CST Reference Sheet
If you don’t have time to watch a few examples
done, and just want to skip to a numbered list of
steps, click the stopwatch below.
We’ll start by drawing a normal boron atom.
B
Boron is element number 5 on the periodic
table, and its chemical symbol is a capital “B”.
Boron atoms can help turn regular
glass into heat-resistant glass.
You’ll be using borosilicate
glassware during labs this year
whenever we need to heat up some
chemicals.
B
5
B
10.81
Step #1 in drawing an atom in Mr. Barnes’
class is to copy the element’s box from the
periodic table.
As we’ve noted already, boron is element #5
on the periodic table.
The “atomic number”
of boron is 5.
The atomic number of
an element is how
many protons are in
an atom of that
element.
Protons are found in
the nucleus of an
atom, which is in the
center of the atom.
So, the next step is to
draw the protons.
You should make
your protons about as
big as a pencil eraser.
REALITY CHECK!
B
5
B
10.81
In a real nucleus, the protons would be
mixed in with neutrons, but here we’re
drawing them clumped together with their
own kind, as though they liked each other.
According to the “liquid drop” model of the nucleus, the protons
and neutrons move around a lot, like people wandering around in
a crowded party.
When free to move, protons will try to get away from each other
as much as they can, since they find each other’s positive electric
charge to be quite repulsive.
In fact, if it weren’t for the “strong force” holding the nucleons
together, the protons would just fly out of the nucleus altogether,
disgusted by each other’s positivity.
REALITY CHECK!
B
5
B
10.81
In a real nucleus, the protons would be
mixed in with neutrons, but here we’re
drawing them clumped together with their
own kind, as though they liked each other.
According to the “liquid drop” model of the nucleus, the protons
and neutrons move around a lot, like people wandering around in
a crowded party.
When free to move, protons will try to get away from each other
as much as they can, since they find each other’s positive electric
charge to be quite repulsive.
In fact, if it weren’t for the “strong force” holding the nucleons
together, the protons would just fly out of the nucleus altogether,
disgusted by each other’s positivity.
Anyway, the next step in drawing an atom is
to figure out how many neutrons to draw.
B
11S
5
B
10.81
Although all boron atoms have five protons, a
boron atom can have any number of
neutrons, in theory.
Realistically, though, if an
atom has too many
neutrons or too few
neutrons, it will be
unstable and fall apart.
Such unstable atoms are
called “radioactive” and
they’re very dangerous.
Let’s assume, though, that
the atom we’re drawing is
a typical boron atom, an
example of the “isotope” of
boron that has the usual
number of neutrons
To get the number of
neutrons for a typical atom of
an element, round the
average atomic mass of the
element to the closest whole
number.
B
11S
5
B
10.81
The funny looking symbol next to the eleven,
“S”, is called “sigma”, and it’s the letter “S”
from the Greek alphabet.
Sigma is a symbol used in math and science
to represent “sum” or “total”.
I use it here because
when you round the
average atomic mass to
the closest whole
number, you get the
“mass number” of the
most common isotope of
the element.
The mass number of an
atom is the total number
of things in the nucleus of
the atom.
In other words, the mass
number is the sum of the
number of protons and
the number of neutrons
added together.
B
11S
-5
6
5
B
10.81
Now, it stands to reason that if there are
eleven total things in the nucleus and five of
them are protons, the other six must be
neutrons. Let’s do the math to show this.
When you’re drawing an atom, once you’ve
got your mass number, you subtract the
atomic number, which is the number of
protons.
Mass number – atomic number = number of neutrons.
I like to use black circles to represent neutrons because when you
fill in a circle with blackness, there’s no room to write anything in
the circle -- no room for a plus, no room for a minus. Draw
neutrons just as big as you draw protons, and shade them in.
Neutrons are neither positive nor negative. They’re neutral.
B
11S
-5
6
5
B
10.81
Now that we’ve drawn the protons and
neutrons, we’re done drawing the nucleus of
the atom.
However, an atom just isn’t an atom unless
it’s got some electrons orbiting the nucleus.
The letter “B” representing this boron atom doesn’t have any plus
or minus signs attached to it, so this boron atom is assumed to be
neutral.
If an atom is neutral, the number of minuses equals the number of
plusses. Therefore, the number of electrons equals the number of
protons. This boron atom has five electrons.
Where and how do we draw those five
electrons?
B
11S
-5
6
5
B
10.81
This is one of the places where the drawing
becomes VERY unrealistic, but we’re going
to ignore that and draw it nice and pretty
anyway.
As you will learn soon enough, the properties of the elements
follow a repeating rhythm on the periodic table.
Let’s look at the PT for a second and see what I mean.
Most of the elements in the first column
of the periodic table, the “alkali metals”,
react violently with water.
The elements at the far right hand side of
the table are all “noble” gases that don’t
react with anything.
The elements in column 7A, the
“halogens”, are all reactive nonmetals
that form salts when combined with
metals.
B
11S
-5
6
5
B
10.81
Because of the rhythmic patterns in the
periodic table, scientists regard electrons as
existing in “shells”
The shells are nested around the nucleus of
the atom like the layers in an onion.
The number of layers in an atom depends on which row of the
periodic table it’s from
Since boron is from the second row of the periodic table, it only
has two shells.
B
11S
-5
6
5
A normal boron atom has five electrons
existing in two shells, but how many
electrons are in each shell?
B
10.81
Once again, for our answer, we go to the periodic table.
Because there are only two elements in
the first row of the periodic table, the first
shell can hold only two electrons.
Because there are eight elements in the
second row of the periodic table, the second
shell can hold only eight electrons.
. . . and so on . . .
B
11S
-5
6
5
B
10.81
The first shell is
full. We can put
electrons in the
2nd shell now.
Electrons are negative and protons are
positive, so electrons try to get as close to the
nucleus as possible.
Electrons feel an “electrostatic” attraction
toward the protons in the nucleus because of
their electric charges.
The second
shell isn’t full,
but we’ve got
five electrons
now, so that’s it.
Therefore, you should always fill the lowest shell with electrons
before you start putting electrons in the farther-out shells.
neutral, so #
B
11S
-5
6
5
=#
5
5
B
10.81
Awesome atom!
Great job!
You need to draw the atom, but you also need to
If I ever ask you, on a test, to draw an atom, this is
show, with numbers, arrows, and symbols, how
what your paper should look like.
you got the amount of each particle.
Q1: What are the three main subatomic particles that atoms
are made of?
A: protons neutrons, and electrons
Q2: Where are protons, neutrons, and electrons found?
A: Protons and neutrons are found in the nucleus. Electrons
orbit the nucleus, grouping into shells.
Q3: What determines the number of protons in an atom?
A: The atomic number of the element is the number of
protons in any atom of that element.
Q4: What is the equation for number of neutrons?
A: # neutrons = mass number – atomic number
Q5: If you are not given the mass number of an atom, how
should you determine the mass number?
A: Round the average atomic mass of the element to the
closest whole number.
Q6: In what kind of atoms is the number of electrons equal to
the number of protons?
A: neutral atoms only
Q7: How many electrons can fit in each shell?
A: two in the first, eight each in the second and third, 18@ in
the 4th & 5th, and 32@ in the 6th & 7th shells.
Now, let’s try a slightly more complicated atom.
Sometimes, an atom’s symbol will have a
number in the upper left superscript position.
15
O
This is the mass number of the atom.
The mass number tells you which isotope of
the element the atom belongs to.
If the mass number is very close to the
average atomic mass of the element, the
atom probably isn’t radioactive.
If the mass number of the atom is
substantially different from the average atomic
mass of the element, the nucleus of the atom
will probably be unstable and dangerous.
When it decays, it could cause the dreaded
disease cancer by causing genetic mutations
in your DNA.
15
O
The real reason an isotope with a weird mass
number is radioactive is because of the
following equation:
Mass number = number of protons + number
of neutrons
As we said before, if an atom has too many
neutrons or too few neutrons, that makes the
nucleus radioactively unstable.
What does the “15” on this oxygen atom’s
symbol mean?
The mass number of this particular oxygen
atom is fifteen.
This particular atom belongs to the isotope
“oxygen-15”.
Is this isotope of oxygen radioactive?
15
O
The average atomic mass of oxygen is 16.00,
so the isotope oxygen-15 probably is
radioactive.
It turns out that oxygen-15 is radioactive. It’s
very unstable, in fact, so unstable that it has a
“half-life” of only 122.24 seconds.
That’s a short amount of time, which means
oxygen-15 atoms decay very quickly.
This doesn’t affect our drawing, though, so
let’s continue.
15
O
8
O
15S
-8
7
16.00
8
As always, the first step in drawing the
atom is to copy the correct box from
the periodic table.
The atomic number of oxygen is eight,
so this atom is going to have eight
protons.
Because this atom has a mass number
specified, we ignore the average
atomic mass of oxygen when
calculating the number of neutrons.
Instead of using 16, we use 15 as our
mass number.
Otherwise, the neutron math is the
same as the last atom.
Now we have enough information to
draw the nucleus of the atom.
15
O
8
O
15S
-8
7
16.00
8
As always, the nucleus of an atom is in
the center of the atom.
That’s a great nucleus, but we still
need electrons to complete the atom.
Like the boron atom we did before, this atom of oxygen has no
electrical charge indicated in the upper right superscript position.
Like the boron atom before, this oxygen atom is neutral.
In this atom, # of electrons = # of protons, so there are eight
electrons.
neutral, so #
15
O
8
O
15S
-8
7
16.00
8
=#
8
Here’s how I want you to show your
line of reasoning on your paper on
tests . . .
Where do we put our eight electrons?
In shells, just like before.
neutral, so #
15
O
8
O
15S
-8
7
8
=#
8
How do we draw a shell?
Yes, as a nice, big circle.
16.00
How many
electrons can fit
into the first shell?
Two.
What if you forget that only two electrons go in the first shell?
Look at the periodic table and count the number of elements in the
first row.
neutral, so #
15
O
8
O
15S
-8
7
16.00
How many
electrons go in the
2nd shell?
8–2=6
8
=#
8
How do we draw the 2nd shell?
As an even bigger circle.
neutral, so #
15
O
8
O
15S
-8
7
16.00
8
=#
8
Q7: What do you call a number that appears to the upper left
or the upper right of an atom’s chemical symbol?
A: a “superscript”
Q8: What piece of information appears in the left superscript
position in an atom’s symbol?
A: mass number
Q9: What does an atom’s mass number tell you about that
atom?
A: which isotope the atom belongs to; total # of protons &
neutrons & # of neutrons when atomic # subtracted from it.
Now, we need to draw some ions.
2+
Be
4
4
Be
9.01
This is a beryllium atom, so it is guaranteed to have four protons.
2+
Be
4
4
Be
9S
-4
5
9.01
No mass number is specified, so we round the
average atomic mass to the closest whole number to get the
mass number of this very typical beryllium atom.
2 missing
2+
Be
4
, so 4 – 2 =
2
4
Be
9S
-4
5
9.01
With only two
electrons, we need
only one shell to
stick them in.
The positive electric charge indicates that there are
missing electrons. The number two tells us how many.
If this atom were neutral, it would have just as many electrons as
protons (4), but two electrons are missing,
so the atom has two electrons in its possession.
2 missing
2+
Be
4
Be
9S
-4
5
9.01
, so 4 – 2 =
4
2
3 extra
13
C
3-
6
C
13S
-6
7
12.01
, so 6 + 3 = 9
6
3 extra
13
C
3-
6
C
13S
-6
7
12.01
, so 6 + 3 = 9
6
Q10: What is an ion?
A: an atom with a non-zero electric charge (must be + or – but
can’t be neutral)
Q11: What makes an ion have a positive electric charge? A
negative electric charge?
A: losing electrons  positive charge;
gaining electrons  negative charge
OR
A: more protons than electrons  positive charge; more
electrons than protons  negative charge.
Q12: Given an equation for number of electrons.
A: # of electrons = atomic number – electric charge
Let’s do some more to make sure everybody
remembers how to do this.
neutral, so #
2
H
1
H
2S
-1
1
1.01
1
=#
1
2 extra
2-
O
8
O
16S
-8
8
16.00
, so 8 + 2 = 10
8
Atom-Drawing Steps
1. # of protons = atomic number of element (see PTotE)
2. If mass number is not given, round average atomic mass to
closest whole number to get mass number.
3. # of neutrons = mass # - atomic #
4. # of electrons = atomic number – electric charge
5. Draw protons and neutrons together in center to form nucleus
6. Do the following until you run out of electrons:
Put 1st 2 e- in 1st shell.
mass
electric
Put next 8 e- in 2nd shell.
number
charge
Put next 8 e- in 3rd shell.
Put next 18 e- in 4th shell.
13 3Put next 18 e- in 5th shell.
Put next 32 e- in 6th shell.
Put next 32 e- in 7th shell.
chemical
e- = electron
PTotE = periodic table of the elements
symbol
C
Now, try drawing the atoms listed on the back of the
“Atom Drawing Worksheet”
Atom Drawing Worksheet
Press the green button below if and when you want
to open up the Atom Drawing Worksheet Answer
Key Power Point. It shows you, step by step, how
each atom on the worksheet is supposed to be
drawn.
Atom Drawing Worksheet
ANSWER KEY
Power Point green button
What follows is just a junkyard of
construction scraps.
POWER POINT OVER.
GO AWAY!