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AP Chemistry Chapter 3 – The Structure of the Atom
____________________ was the early (around 400BC) Greek philosopher who is credited with the concept of the atom (atomos) –
which means ____________________
____________________ (around 1800AD) is an English school teacher who proposed the law of conservation of mass, the law of
definite proportions, and the law of multiple proportions. His many experiments with gases proved these law are true, if atoms exist. He
is also known as the ____________________________________________________________
Dalton’s atomic theory
1.
All matter is composed of very small particles called ____________________
2.
Atoms of a given element are identical in ____________________, ____________________, and other properties; atoms of
different elements differ in these properties.
3.
Atoms cannot be ____________________, ____________________, or ____________________
4.
Atoms of ____________________ elements combine in simple ____________________ ratios to form chemical compounds.
5.
In chemical reactions, atoms are ____________________, ____________________, or ____________________
Two aspects of Dalton’s atomic theory proven to be incorrect:
a.
We now know atoms are ____________________
b.
Atoms of the same element can have different ____________________
____________________ is the man credited with the discovery of the electrons in the late _____, using cathode ray tubes.
____________________ discovered the mass of the electron.
Knowledge of electrons led to two inferences about atomic structure:
1.
Because atoms are electrically ____________________, they must contain ____________________ charge to balance the
negative electrons.
2.
Because electrons have so little mass, atoms must contain other particles to account for most of their ____________________
Nucleus of the atom—discovered by ________________________________________
Gold foil experiment—actually done by ____________________ and ____________________
Observations:
a.
Majority of the ____________________ particles penetrated foil ____________________
b.
About ____________________ in ____________________ were ____________________ deflected
c.
About ____________________ in ____________________ were deflected ____________________
Conclusions:
1.
___________________ of the atom and the ____________________ charge are concentrated in small regions called
____________________
2.
Most of the atom is ______________________________.
3.
__________________________of charge on the nucleus is__________________ for different atoms.
4.
Number of ____________________ outside the nucleus = number of units of ____________________ (to account for the fact
that the atom is electrically ____________________
Atoms are electrically neutral because they contain equal numbers of ____________________ and ____________________
A couple years later Rutherford presented evidence for a neutral particle which was also in the nucleus and contained a similar mass to
that of a proton – called a ____________________________________
Mass of one____________________= mass of one ____________________= mass of 1837 ____________________
Thus the total mass of an atom is basically the sum of the protons and neutrons, called the ___________________
___________________ or ____________________ ____________________, abbreviated A.
Atomic number

number of ____________________in the ____________________of the atom.

number of ____________________ ____________________ the element and is equal to the number of
____________________

symbol is Z.
____________________are atoms of the same element that have different masses because they have different numbers of
____________________, but they still have similar chemical ____________________
____________________is the general term for any isotope of any element
______________ _____________
___________ (1 _______) is exactly 1/12 the mass of a carbon-12 atom.
______________ _____________ _____________ is the weight average of the atomic masses of the naturally occurring isotopes of an
element.
Ave. Atomic mass = (%abundance × mass of isotope 1) + (%abundance × mass of isotope 2) +…..
Example 1:
Element Sciencium has two isotopes. Sciencium-301 has an abundance of 59.5%, and Sciencium-304 is the other. What is the average
atomic mass?
Example 2:
Element Pepsium has an average atomic mass of 335. Two isotopes of Pepsium exist. If Pepsium-327 is 30.5% abundant, then what is
the second isotope?
Mass Spectrometry
A mass spectrometer has three parts:
1. ionizer
2. magnetic field
3. detector
And might look like this →
If a sample of a pure element is placed in the spectrometer,
then all the ions formed will have the same charge. For
example Cl → Cl-
The ions then pass through a magnetic field that will change
their paths. Which will change direction more, something
heavy or something light?
The computer attached to the detector gives a readout like
this →
The locations tell the masses – one group of Cl had a mass
of 35 amu’s and the other had a mass of 37 amu’s.
The sizes of the bars indicate the relative amounts of each
isotope.
As the bar for 35Cl is 3 times bigger than 37Cl (measuring
with a ruler) 35Cl is about 75% abundant and 37Cl is about
25% abundant.
Unstable Nuclei and Radioactive Decay
1) When referring to nuclear reactions people commonly think of nuclear ____________________ (the
____________________ of large atoms into smaller pieces) and nuclear ____________________ (the
____________________ of small atoms into one large one), but on earth these reactions do not occur naturally.
2) Naturally occurring nuclear reactions result from the unusual number of neutrons of an isotope which makes it
____________________ (unusually high in energy). This often results in the isotope ____________________ from
one element into another element in an attempt to become more stable (lower in energy).
A) These reactions are called ____________________ reactions, as they involve changes in the nucleus.
B) During these nuclear reactions, rays and particles are given off, which is called ____________________.
C) Sometimes an unstable nucleus will change into many different elements as it tries to become more stable. This is
called ____________________ decay.
3) When radioactive decay occurs, there are three different types of radiation that can be given off. Each type has a
different ____________________, and sometimes a ____________________.
A) The first type of radiation to be discovered was called ____________________ radiation and came from alpha
particles.
226
222
??
88
Ra →
86
Rn +
i)
??
??
Because the mass numbers must be equal, 226 = 222 + x. So the mass of the alpha particle must be
____________________.
ii) Because the atomic numbers must be equal, 88 = 86 + x. So the atomic number of the alpha particle must be
____________________.
iii) The element ____________________ has a mass of 4 and an atomic number of 2, so the alpha particle is just
like a helium atom without any electrons;
4
4
or
2
2
He

B) The second type of radiation to be discovered was called ____________________ radiation and came from beta
particles.
14
14
??
6
C →
7
N
+
??
??
i) Because the mass numbers must be equal, 14 = 14 + x. So the mass of the beta is ____________________.
ii) Because the atomic numbers must be equal, 6 = 7 + x. So the atomic number must be
____________________.
iii) The ____________________ has a mass of zero and a charge of -1, so the beta particle is just like an electron;
0
-1
β
C) The last type of radiation to be discovered was called ____________________ radiation and came from gamma
particles.
238
234
4
??
92
U →
90
Th +
2
He +
??
??
i)
Because the mass numbers must be equal, 238 = 234 + 4 + x. So the mass of the gamma particle must be
____________________.
ii) Because the atomic numbers must be equal, 92 = 90 + 2 + x. So the atomic number must also be
____________________.
iii) The gamma particle was the last to be found because it has no ____________________ and no
____________________;
0
0
γ
The Development of a New Atomic Model
Previously, Rutherford reshaped our thought of the atom by showing the protons were located in the _____________________ of the
atom, but he could not model for us where the electrons were, other than outside the nucleus somewhere. Fortunately, studies into the
properties of light and the effects of light on matter soon gave clues to where electrons actually are.
Light is a small part of all the radiation (something that spreads from a source) called _____________________ radiation.
Electromagnetic radiation is _____________________ in the form of waves (of electric and magnetic fields). Electromagnetic radiation
includes radio waves, microwaves, infrared, visible light, X-rays, and Gamma rays. All these together are considered the
Electromagnetic _____________________
As all the forms of electromagnetic radiation are waves, they all have similar properties.

All electromagnetic radiation travels at the ________________ ___ _____________ (c), 299,792,458 m/s (3 x 10 8) in a
vacuum

The _____________________ is the top of the waves, the _____________________ is the bottom of the waves, and the
_____________________ is a measurement from the rest or zero line to a crest or trough

The _____________________ (λ – lambda) is the distance between successive crests/troughs and is measured in
_____________________ (often nm = 1 x 10 -9 m)

The _____________________ (ν – nu) is the number of waves that pass a point in one second and is measured in
_____________________ (per second – can be written as s-1) or Hz (Hertz)
c
The speed of a wave is directly proportional to the wavelength and the frequency; c = λν is the formula.
λ
Example: A certain violet light has a wavelength of 413 nm. What is the frequency of the light?
ν
Unfortunately, thinking of light as waves led to a problem. It was noticed that if light strikes a metal, then sometimes it could cause
_____________________ to be emitted (leave the atoms entirely – like in a solar panel); called the _____________________ effect. If
light was a wave, then all amounts of light energy should cause this to happen, but this was not the case. It always took some
_____________________ amount of energy to get the electrons to be emitted. This lead Max Planck to theorize that light must carry
energy in basic minimum amounts that he called _____________________ Like a delivery person cannot correctly deliver half a box, the
electrons in atoms cannot gain a fraction of a quantum of energy (it has to be in _____________________ numbers). He proposed that
this energy was directly proportional to the frequency of the electromagnetic radiation and a constant, now called Planck’s constant.
E=hν
where
E
E = energy, measured in Joules (J)
h = Planck’s constant, 6.626 x 10-34 Js
ν = frequency, in 1/s
h
ν
Example: What is the energy content of one quantum of the light with a wavelength of 413 nm?
In 1905 Einstein used Planck’s work to propose that electromagnetic radiation had a dual ______________-_____________________
nature. As a particle, electromagnetic radiation carries a quantum of energy of energy, has no mass, and is called a
_____________________. So to get an electron to emit from a metal, it must be struck with a photon having quantum energy big
enough, or nothing will happen. Each metal requires different quantum energy, thus each metal can be identified by the frequency of
light needed to emit electron.
This idea was expanded upon to develop an idea of where the _____________________ were in an atom. It was found that low pressure
_____________________ could be trapped in a tube and electrified, and would then glow a color particular to the gas inside.
Furthermore this light could be passed into a prism, and instead of getting the entire spectrum (rainbow) of colors, only certain
wavelengths of light would be seen as small bars of color, called a ________________-_____________________ spectrum.
This would indicated that the electrons in an atom were only absorbing _____________________ amounts of energy from the electricity,
causing the electrons to move from their _____________________ state (normal position close to the nucleus) to an
_____________________ state (higher energy position further away from the nucleus). The electrons do not stay in the excited state for
long and fall back to their ground state, losing the energy _____________________ to what they gained.
Niels Bohr used this to develop a model of the atom where the electrons could only be in certain, specific _____________________ level
(n) orbits around the nucleus. Just as you cannot go up half a rung on a ladder, the electron could not go up a partial energy level. The
electrons gained or lost enough energy to move a _____________________ number amount of energy levels (n) away from or closer to
the nucleus, or it did not move. He calculated the amount of energy needed for an electron of hydrogen to move between each energy
level (n) (which was not constant) and his calculations _____________________ with experimental results.
The _____________________ series of hydrogen spectral lines refer to the four lines seen in the visible light region (the four colored
bars). If the electron was excited to energy level (n) 6, 5, 4, or 3 and fell to energy level (n) 2, the resulting energy given off would have
a frequency in the _____________________ region of electromagnetic radiation. (One line for dropping from 6 to 2, one for 5 to 2, one
for 4 to 2, and one for 3 to 2).
However, there are other possibilities. If the electrons drop from n=6, 5, or 4 to n=3, then the energy given off is not big enough to be
seen as it is in the _____________________ region. These three lines in the infrared region are referred to as the
_____________________ series. If the electrons drop to n=1, then the five lines given off are too high in energy to be seen, as they are
in the _____________________ region. These lines are referred to as the _____________________ series.
Model of Atom Review:
1.
Thomson’s Plum Pudding Model – the atom is a ball of evenly spread _____________________ stuff with random
_____________________ particles (electrons).
2.
Rutherford’s Nuclear Model – the atom has a central _____________________ containing the positive particles (protons) with
the electrons outside.
3.
Bohr’s Orbital Model – The electrons circle the nucleus in specific energy _____________________ like the planets orbit the
sun. Unfortunately this only works for atoms with _____________________ electron…
4.
Quantum Mechanical Model – electrons are found in specific _____________________ around the nucleus, but the exact
location of the electrons inside the regions _____________________ be determined
The quantum mechanical model starts with a _____________________ Quantum Number (n), which is the basic energy level of an
electron, and often matches the _____________________ number. Possible values (currently) are 1-7.
Inside the principal quantum energy level are sublevels that correspond to different _____________________ shapes. The sublevels are
designated as s (sharp), p (principal), d (diffuse), and f (fundamental).
Inside the sublevels are orbitals, specific regions with a 90% probability of finding electrons.

s –orbitals are _____________________ shaped clouds around the nucleus

p -orbitals are _____________________ shaped clouds with the nucleus between the lobes

d and f are much more complex in shape
Each sublevel has room for a different amount of electrons, because an orbital can hold two electrons, then each sublevel has a different
amount of orbitals

s –sublevel can hold _____________________ electrons, so it has_____________________ orbital (shape)

p –sublevel can hold _____________________ electrons, so it has _____________________ orbitals (shapes)

d –sublevel can hold _____________________ electrons, so it has _____________________ orbitals (shapes)

f –sublevel can hold _____________________ electrons, so it has _____________________ orbitals (shapes)
To know the maximum amount of electrons that could be in any principal quantum level (and the number of elements that could be
represented) use the formula 2n2
if n=1, then _____________________ electrons will fit
if n=4, then _____________________ electrons will fit
In order to show on paper where electrons are likely to be located in an atom, orbital filling diagrams and electron configurations are
drawn or written. When this is done, three rules must be followed:
1.
_____________________ principle – electrons fill lower energy levels first, thus 1 before 2 and s before p, etc.
a.
orbitals within a sublevel are _____________________ in energy (called degenerate)
b.
the principal energy levels often _____________________ making them seem a little out of order
c.
_____________________ are used to represent orbitals
d.
Another way of writing the aufbau principal diagram:
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p
2.
3.
________________Exclusion Principle – an orbital (box) can hold a maximum of two electrons (arrows)
a.
for two electrons to fit, they have to have _____________________ spins
b.
↑ for _____________________ electron in the orbital
c.
↑↓ for _____________________ electrons in the orbital (opposite spins)
________________Rule – when electrons occupy degenerate orbitals, one electron is placed into each orbital with parallel
spins before doubling up
____ ____ ____
3p
NOT
____ ____ ____
3p
(For a web-based model of what was shown in class, visit: http://intro.chem.okstate.edu/WorkshopFolder/Electronconfnew.html)
Orbital Notation shows the arrows in the boxes to represent the electrons in an atom. To shorten this process, an electron configuration
can be written. It leaves out the information about the number of orbitals in each sublevel, so it will be expect you remember that
information.
It has the general form ________________
n = principal quantum number (1-7…)
l = sublevel letter (s, p, d, or f)
° = number of e- in that orbital (1-14)
Examples:
Ni
_____________________________________________________________________
Sn
_____________________________________________________________________
If writing out the entire electron configuration is too much, we can use the previous (in the periodic table) _____________________ gas
to take the place of part of the electron configuration:
Examples:
Polonium:
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4
Xenon:
1s22s22p63s23p64s23d104p65s24d105p6
Polonium:
[Xe] 6s24f145d106p4
When the electron configuration is written for an element using the noble gas configuration the electrons written after the noble gas are
the ones that appear on the _____________________ of the atom. These electrons are called _____________________ electrons. When
elements bond to form compounds, it is these electrons that are involved. The _____________________ of valence electrons makes a
big difference in how the element will bond, so to make it easy to predict, we draw electron _____________________ diagrams.
A) In an electron dot diagram, we use the _____________________ of the element and dots to represent the number of
valence electrons.
B) Only s and p electrons with the _____________________ quantum number count for dot diagrams, even if there are d and
f electrons after the noble gas.
Examples:
Lithium
Li
Beryllium
Be
Boron
B
Carbon
C
Nitrogen
N
Oxygen
O
Fluorine
F
Neon
Ne
_________________________ - properties of the elements are a periodic function of their atomic numbers.
The earliest and most successful arrangement of the elements was by Dmitri Mendeleev in the 1870s. He arranged the
elements known at that time by their _______________ and _______________ properties into groups. His arrangements
of the elements left some gaps, which he claimed were elements not yet discovered. With his table he predicted the
characteristics of these missing elements, and was correct.
During the 1910s, Henry Moseley used x-ray spectra to determine the _______________ _______________ (number of
protons) for elements and proved that each element had a different amount of protons. Moseley rearranged the elements
based on atomic number, as it is arranged today, and found gaps which he also claimed were undiscovered elements. Some
of these elements were found quickly, while others were not found until after his death due to their highly radioactive
(unstable) nature.
There are three key items in understanding and explaining all the trends (and exceptions) on the periodic table.
1.
1.
_______________________________________
2.
_______________________________________
3.
_______________________________________
Effectice Nuclear Charge – pull of the _______________ in the nucleus on the valence (outer) energy level electrons.
The greater the _______________ _______________, the greater the number of protons, and the greater the
_______________ _______________ _______________. Effective nuclear charge has the greatest effect moving
from _______________ to _______________ across a period (it increases).
Which element has more effective nuclear charge, P or S? _______________
Which element has more effective nuclear charge, S or Se? _____________________________________________
2.
Energy levels – the principal quantum level of the electrons, sometimes called _______________. As elements
increase in atomic number they also increase in the number of _______________. These electrons occupy higher and
higher energy levels. Higher numbered energy levels are _______________ away from the nucleus. Energy levels
have the greatest effect moving from _______________ to _______________ within a group (it increases).
Which element has more energy levels, S or Se? _______________
Which element has more energy levels, P or S? _____________________________________________
3.
Coulomb’s Law state that the force of attraction between things is directly proportional to the _______________ of the
charge and inversely proportional to the square of the _______________ between them. What two things are attracted
to each other in an atom? _________________________________________________________________________
Which one can move? _____________________________
Which situation would show the stronger force of attraction? Explain _________________________________________
+
2p
-
1e
+
12p
-
1e
Which situation would show the stronger force of attraction? Explain _________________________________________
+
2p
-
1e
+
2p
-
1e
For the following trends, you must know the general trends (memorize), but using the three key items you must be able to
explain the trend as well (understand).
1.
_______________ _______________ - size of the atom
a.
_______________ from top to bottom within a group
Why does it increase from top to bottom? ____________________________________________________________
b.
_______________ from left to right within a period
Why does it decrease from left to right? ____________________________________________________________
2.
_______________ _______________ - energy required to _______________ an electron from a gaseous atom
a.
_______________ bottom to top
Why is it easier to remove electrons from atoms at the bottom of the P.T.? ______________________________
__________________________________________________________________________________________
b.
_______________ left to right
Why is it easier to remove electrons from atoms at the left of the P.T.? ______________________________
__________________________________________________________________________________________
c.
This is sometimes called _______________ _______________, as metals tend to lose electrons easily.
Which element would exhibit the most metallic character? _____________________________________________
3.
_______________ _______________ - energy released when an electron is added to a gaseous atom
a.
_______________ bottom to top
Why is more energy released when electrons are added to atoms at the top of the P.T.? _____________________________
b.
_______________ left to right
Why is more energy released when electrons are added to atoms at the right of the P.T.? ___________________________
c.
This is sometimes called _______________ _______________, as nommetals tend to gain electrons
easily.
Which element would exhibit the most nonmetallic character? _____________________________________________
4.
______________________________ - measure of an atom’s pull on another atom’s electrons
a.
_______________ bottom to top
Why are atoms at the top of the P.T. able to pull stronger on a different atom’s electrons? __________________________
__________________________________________________________________________________________
b.
_______________ left to right
Why are atoms at the right of the P.T. able to pull stronger on a different atom’s electrons? _________________________
__________________________________________________________________________________________
5.
_______________ - charged atoms
a.
_______________ - _______________ ion formed from an atom losing an electron. The ionic radius is
always _______________ than the original atom. Why? ______________________________________
b.
_______________ - _______________ ion formed from an atom gaining an electron. The ionic raidus is
always _______________ than the original atom. Why? ______________________________________
Let’s summarize the trends. Remember you must know the trends (memorize), but you also need to be able to explain why
the trend exists.