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Atoms in a Nutshell
All matter is made up of tiny particles
called atoms.
•
There are about 92 naturally
occurring elements. (The elements with
numbers over 92 are man made.)
•
Atoms are made up of three main
sub-atomic particles.
– Protons
– Neutrons
– Electrons
tells the
number of protons
and electrons
Atomic number
19
Atomic
Number
39
Atomic Mass
Tells the
number of
protons and
neutrons added
Atomic together.
Mass
Protons and neutrons are found in
the center of the atom. (Nucleus)
Electrons are tiny particles that
zoom around the space OUTSIDE the
nucleus.
Particle
Charge
Protons
Mass
(AMU)
1
Neutrons
1
Neutral
Electrons
Insignificant
1/1800th
-
+
Rutherford Lab
Purpose: to mimic Rutherford's famous gold foil experiment.
Materials: marble (alpha particle), cardboard models, plain paper, ruler.
Procedure: [Summarize procedure in 2 – 3 sentences]
1.
Pick up a piece of plain paper from the supply area.
2.
Center the paper on top of a cardboard model and tape it down to keep it in
place. Don’t look under the box!
3.
Roll the marble under one side of the box. Observe where the marble comes
out and trace the approximate path on the white paper.
4.
Working from all four sides of the black box, continue to roll the marble under
the board, making observations and tracing the rebound path for each marble
roll. Roll the marble at least 20 times from each side of the box. Vary the
angles at which the marble is rolled into the box.
5.
After sketching the apparent path of the marble from all sides and angles, the
general size and shape of the unknown target should emerge in negative form
from the area where there are no lines.
6.
Form a working hypothesis of the unknown target by sketching the shape on
your plain paper. Based on your hypothesis, repeat as many marble rolls as
necessary to either confirm or revise your structure.
Data:
Make a 10 X 10 cm square to record your data.
Rutherford Lab Conclusion
Analysis:
1. Skim pages 111 to 112 in the textbook. In what
ways does this activity simulate Rutherford’s
experiment?
2. Briefly describe Rutherford’s experiment and
what he observed.
3. As a result of his observations, what did
Rutherford conclude about the structure of the
atom?
NIELS BOHR
Atom Models
Protons and Neutrons are found in the
center of the atom. We call the area with
the protons and neutrons the nucleus.
Electrons are found zooming around the
outside. They are in different energy
levels.
-Inner level has space for 2 electrons.
-2nd level has space for 8 electrons.
-3rd level has space for 18 electrons
Things to KnOw…
• Every element wants to have a full outer
orbit – then they are stable – so…
• if an element has it’s 1st orbit full and
stable – it will have 2 valence e• if an element has it’s 2nd , or 3rd orbit full
and stable – it will have 8 valence e- (we
call that a Stable octet)
• Everything wants to bind together to get a
maximum of 8 valence e- shared between
them – then they are stable!!
Which Element is this?
• Atomic #
• Atomic Mass
• Valence
Electrons
Which Element?
Which Element?
Bohr Models…
Niels Bohr explained the structure of the atom in his “Bohr models”. His model of the atom resembles a solar system. P:9
N:19
So how do we draw a Bohr model …?
• Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table)
• Next place some orbits around it
P:11
N:12
P:11
N:12
• Next figure out how many e‐ are in sodium (look at your periodic table). Place them in dots in the orbits
Sodium has 11 electrons !! they are the same as the protons
P:11
N:12
• Bohr models show – the protons and neutrons in the nucleus. – the electrons in orbits or shells
• Each orbit/shell can only hold a certain # of electrons and then it is full. P:3
N:4
Some Bohr models…
Oxygen
P:8
N:8
P:13
N:14
8p+
8n
8e-
Aluminium
13 p+
14 n
13 e-
Lewis Dot Diagrams…
• Gilbert Lewis used a different model than Bohr, and he only showed the valence e‐ in it. • His model is called the Lewis dot structure . He put dots around the symbols so that we can see just the valence electrons for the elements (so we can easily see which e‐ are going to react) Lewis Model
• Shows only the electrons in the outermost level. Called “Valence Electrons”
• Valence Electrons determine how elements react.
• Write the symbol with 1 – 8 dots around it.
• Elements have a maximum number of 8 valence electrons.
The red dots show you the VALENCE ELECTRONS in
each element’s atoms
See the difference??...
Lewis just shows the valence e‐
P: 11
N:12
Bohr model
of Sodium
Atom
Na
Lewis
Structure of
Sodium Atom
How to calculate atomic mass
Problem #1: Carbon
mass number --exact weight - percent abundance
12 --------------12.000000 ------98.90
13 --------------13.003355 ------1.10
To calculate the average atomic weight, each exact atomic
weight is multiplied by its percent abundance (expressed as a
decimal). Then, add the results together and round off to an
appropriate number of significant figures.
This is the solution for carbon:
(12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu
Atomic Mass
•
•
•
•
Magnesium has three
isotopes.
78.99% magnesium 24 with
a mass of 23.9850 amu,
10.00% magnesium 25 with
a mass of 24.9858 amu,
11.01 magnesium 26 with a
mass of 25.9826 amu.
What is the atomic mass of
magnesium?
Isotope
Percent
Abundance
Mass
Mg-24
78.99
23.9850
18.94575
Mg-25
10.00
24.9585
2.49585
Mg-26
11.01
25.9826
2.86068
24.304 amu
Atomic Mass
Calculate the atomic mass of copper if copper has two
isotopes. 69.1% has a mass of 62.93 amu and the rest has
Percent
a mass of 64.93 amu.
Isotope
Mass
Abundance
Cu-63
69.1
62.93
43.48463
Cu-65
30.9
64.93
20.06337
63.548
A.A.M.  (0.691)(62.93 amu)  (0.309)(64.93 amu)
A.A.M.  43.48463 amu  20.06337 amu
A.A.M.  63.548 amu for Copper
Cu
63.548
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