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IB Chemistry II
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First Periodic Tables were much different than
the one today
First Periodic table had 100 elements
Elements
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Simplest form of matter and can’t be broken down
into simpler componets
Atoms
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Smallest unit of an element
There are 92 elements that occur naturally
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J. J. Thompson
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Discovered that different metals produce a stream of
negatively charged particles when a high voltage is
applied across 2 electrodes= electrons
These were the same regardless of the metal.
Atoms have no charge
Plum pudding model: Negative ions scattered
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Fired alpha particles at a piece of gold foil. So,
he hypothesized that these particles should
pass straight through or get struck in the
positive sponge.
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Protons and neutrons are present in the
nucleus of an atom. Electrons are in orbits or
energy levels around the nucleus.
The relative masses and relative charges of the
sub atomic particles are:
Relative Mass
Relative Charge
Proton
1
+1
Neutron
1
0
Electron
5x10-4
-1
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Atomic Number (Z)=number of protons. It is
the fundamental characteristic of and element
Mass Number(A)=number of protons +
neutrons
Isotopes:
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Are atoms with the same atomic number, different
mass number or the same number of protons, but
different number of neutrons.
Number of Protons=Z
Number of Electrons=Z-q
Number of neutrons=A-Z
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All matter is composed of tiny indiviable
particles called atoms
Atoms can’t be created or destroyed
Atoms of the same element are alike in every
way
Atoms of different elements are different
Atoms can combine together in small number
to form molecules.
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What do atoms look like. Kind of like hard spheres
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• Isotopes differ in physical properties that
depend on mass such as:
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density,
rate of diffusion, etc.
This difference is very significant for the isotopes of
hydrogen as deuterium has the twice the mass of the
more abundant . As isotopes have the same electron
arrangement they have the same chemical properties.
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• Examples of the uses of radioisotopes: C-14
in radiocarbon dating,
CO-60 in radiotherapy and
I-131 and I-125 as medical tracers.
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Show the same chemical properties, as a
difference in the number of neutrons makes no
difference to how they react and so they
occupy the same place in the periodic table
Chlorine exist as 2 isotopes:
 35Cl
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and 37Cl The average relative atomic mass of the
isotopes is not 36 but 35.45.
35Cl is the more abundant isotope, in a sample of 100
chlorine atoms, there are 75 atoms of 35Cl and 25
atoms of 37Cl.
How would you calculate the relative atomic mass?
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To work it out first calculate the total mass of
the hundred atoms.
(75 x 35) + (25 x 37) = 3550
3550
=
100
35.5
The 2 isotopes are both atoms of chlorine with
17 protons and 17 electrons
35Cl; number of neutrons: 35-17=18
37Cl; number of neutrons: 37-17=20
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The stability of a nucleus depends on the balance
between the number of protons and neutrons.
When a nucleus contains either too many or too
few neutrons, it is:
Radioactive
 And will change to a more stable nucleus by giving out
radiation
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There are several different forms of radiation
based on ionization and penetration abilities:
Alpha
 Beta
 Gamma
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Carbon-14 dating
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The most stable isotope of carbon is 12C:
 Has 6 protons and 6 neutrons.
 14C
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has
8 neutrons , which is too many to be stable. It can
reduce the neutron to proton ratio when a neutron
changes to a proton and an electron.
The protons stays in the nucleus but the electron is
ejected from the atom as beta particles.

6C
14
 147N + o-1e
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The relative abundances of carbon-14 present in
living plants is constant as the carbon continually
replenishes from carbon present in CO2 in the
atmosphere.
When organisms die no carbon 14 is absorbed and
the levels carbon 14 fall due to decay.
As this process occurs at a regular rate, it can be
used to date carbon containing materials.
The rate of decay is measured in half life
This is the time taken for half the atoms to decay
The carbon-14 to carbon-12 ratio falls by 50% every 5730
years after the death of an organism
 This is what archeologist use to date objects.
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Radiotherapy
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Radiation Therapy
Is the treatment of cancer and other diseases with
ionizing raditation.
Cancerous cells are abnormal cells which divide at
rapid rates to produce tumors that invade
surrounding tissue.
The treatment damages the genetic material inside
the cell by knocking off electrons and making it
impossible for the cell to grow
This therapy damages both cancer and normal
cells, the normal cells are able to recover if the
treatment is carefully controlled.
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Can treat localized
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Solid tumors
 Cancers of
 Skin
 Tongue
 Larynx
 Brain
 Breast
 Unterine cervix
 Blood
 Leukemia
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Colbalt 60 is commonly used as it emits very
penetrating gamma radiation when their protons
and neutrons change their positions in the nucleus.
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Radioisotopes have the same chemical
properties as any other atom of the same
element, and so they play the same role in the
body
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Their positions, unlike other isotopes can be
monitored by detecting radiation levels making
them suitable
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Unstable atomic nuclei will spontaneously
decompose to form nuclei with a higher stability.
The decomposition process is called radioactivity.
The energy and particles which are released
during the decomposition process are called
radiation.
When unstable nuclei decompose in nature, the
process is referred to as natural radioactivity.
When the unstable nuclei are prepared in the
laboratory, the decomposition is called induced
radioactivity
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Alpha Particles:
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Beta Particles
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Emitted by nuclei with too many protons to be stable
Composed of 2 protons and 2 neutrons
Emitted by nuclei with too many neutrons, are
electron which have been ejected from the nucleus
by neutron decay
Gamma Particles
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Are form of electromagnetic radiation
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Mass spectrometry (MS) is an analytical technique
that produces spectra (singular spectrum) of the
masses of the atoms or molecules comprising a
sample of material.
The spectra are used to determine the elemental or
isotopic signature of a sample, the masses of
particles and of molecules, and to elucidate the
chemical structures of molecules,
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such as peptides
and other chemical compounds.
Mass spectrometry works by ionizing chemical
compounds to generate charged molecules or molecule
fragments and measuring their mass-to-charge ratios.[1]
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Vaporization:
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Ionization
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Positive ions are attracted to negatively charged plates.
The positive ions are accelerated by an electric field.
Deflection:
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The gas particles are bombarded with high-energy electrons which knock electrons
which ionize them. Electrons are knocked off the particles leaving positive ions.
Acceleration
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The sample is turned into a gas using an electrical heater
The positive ions paths are altered with a magnetic field at right angles of each other.
The amount of deflection is proportional to the charge mass ratio. Ions with smaller
mass are deflected more than heavier ones. Lighter ions have less momentum and
are deflected more than heavier ions. For a given field, only ions with a particular
mass/charge ratio will make it to the detector.
Detection
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The magnetic field strength is slowly increased. This changes the mass charge ration
of ions that can reach the detector. A mass spectrum is produced. Mass charge ratio
is detected and a signal is sent to a recorder
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) of an element is the average mass of an atom
according to the relative abundances of its
isotopes, on a scale where the mass of one atom
of is 12
For example for 35 17Cl which has two isotopes
(75 %) and 3717Cl(25 %).
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This type of radiation comes in different forms of
different energy
All electromagnetic waves travel at the same
speed (c)
These waves can be distinguished by their
different wavelengths (λ)\
Different colors of visible light have different
wavelengths
 Red light has a lower wavelength than blue
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The number of waves that which pass a particular
point in 1 sec is called:
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Frequency (f)
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Wavelength
Practice formulas:
𝑣
 λ=
𝑓
𝑣
 F=
λ
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units are meters (m)
units are Hz or
1
𝑠
v=f x λ units are m/s
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Forms only a small part of the elctromagnetic
spectrum
Infrared waves have longer wavelengths than
red light and ultraviolet waves have shorter
wavelengths than violet.
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When white light is passed through hydrogen gas, an
absorption spectrum is produced. This line spectrum with
some colors of the continuous spectrum missing
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See diagram on page 51
Evidence of Bohr model
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Hydrogen atoms absorb and emit energy. This picture of the atom
was considered with the electrons orbiting the nucleus in a circular
energy level. Niels Bohr proposed that an electron moves into
orbit or higher energy level further away from the nucleus when
an atom absorbed energy.
 This is called the : Excited state
 This is produced
 It is unstable
 Electrons soon fall back to lowest state=Ground State
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The energy the electron gives out as it falls back into lower
levels is called
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Electromagnetic Radiation
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This energy is called
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Packet of energy=photon
Photons are released for each electron transistion.
The energy of the photon of light emitted is equal
to the energy change in the atom
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∆Eelectron=Ephoton
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It is also related to the frequency of the radiation by
planck’s equation
 ∆Eelectron=hf
 Planck’s Constant =h=6.63x10-34Js
You will use this equation to calculate the
wavelength to break bonds. Page 7 of
chemistry data booklet
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In 1900, Max Planck was working on the problem of
how the radiation an object emits is related to its
temperature.
He came up with a formula that agreed very closely
with experimental data, but the formula only made
sense if he assumed that the energy of a vibrating
molecule was quantized--that is, it could only take on
certain values.
The energy would have to be proportional to the
frequency of vibration, and it seemed to come in little
"chunks" of the frequency multiplied by a certain
constant.
This constant came to be known as Planck's constant,
or h, and it has the value
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Hydrogen atoms gives out energy when an
electron falls from a higher to a lower energy
level.
Hydrogen produces visible light when the
electron falls to the second energy level (n=2)
The transition from to the first energy level
corresponds to a higher energy change and are
in the ultraviolet region of the spectrum.
Infrared radiation is produced when an
electron falls to the third energy level
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Looking at figure 2.13 page 53 HL and 45 SL
show how the energy levels inside the atom.
The lines converge at higher energy levels
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This is due the energy levels inside the atom are
closer together.
 When an electron is at its highest energy e=∞, it is no
longer in the atom and the atom has been ionized.
 The energy needed to remove an electron from the
ground state is called
 Ionization energy
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• The hydrogen spectrum:
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Series
Region
Electron falls to
Lyman
UV
n=1
Balmer
Visible
n=2
Paschen
IR
n = 3–
• The ionization energy of hydrogen
corresponds to the convergence limit of the
Lyman series.
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Atoms react based the arrangement of sub
atomic particles. We can now explore the
structure of the atoms beyond hydrogen.
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Each energy level can hold a limited number of
electrons.
Ground State
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Electrons are placed in the lowest energy level first,
and when this becomes complete, electrons move to
the second energy level, and so on.
Helium has 42H, has 2 protons, 2 neutrons and
2 electrons. The protons and neutrons from the
nucleus and the 2 electrons both occupy the
lowest energy level.
Element
Electron
Arrangement
Element
Electron
arrangement
1H
2He
1
2
11 Na
12Mg
2,8,1
2,8,2
3Li
2,1
13Al
2,8,3
4Be
2,2
14Si
2,8,4
5B
2,3
15P
2,8,5
6C
2,4
16S
2,8,6
7N
2,5
17Cl
2,8,7
8O
2,6
18Ar
2,8,8
9F
2,7
19K
2,8,8,1
10Ne
2,8
20Ca
2,8,8,2
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• The first ionization energy is the minimum
energy required to remove one mole of
electrons from a mole of gaseous atoms to form
a mole of univalent cations in the gaseous state.
It is the enthalpy change for the reaction:
X (g) X + (g) + e–.
When an atom becomes ionized it loses an
electron or proton. e-
Ion
Electron Arrangement
Energy level from
which the next electron
is removed when
ionized
Al
2,8,3
Third
Al+
2,8,2
Third
Al2+
2,8,1
Third
Al3+
2,8
Second
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Bohr model has limitations. It doesn’t explain
levels after level 3.
More energy is needed to remove electrons at
higher ionization energy.
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More difficult to remove, so we have:
-why we have sublevels
See table on page 57 HL.
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we know that the first energy level is made up
of 1s sub level. Due to Heisenberg Uncertainty
principle we don’t know the position of the
electron..
So we just say its in an orbital
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Atomic orbital is a region around the atomic nucleus
in which there is a 90% probability of finding
electron.
S orbitals at either level are spherical/circular
1s and 2s
2s are larger
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P sub levels contain 3 p atomic orbitals of equal
energy.
They are dumbbell shape and are arranged at
right angles
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D orbitals are made up of 5 sublevels
F orbitals are made up of 7 sublevels
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See page 61 HL
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No more than 2 electrons can occupy an one
orbital, and if two electrons are in the same
orbital they must spin in opposite directions
Level
Sublevel
Maximum
number of
electrons ins
subshell
n=4
4f
14 (7 f orbitals)
4d
10 (5 d orbitals)
4p
6 (3 p orbitals)
4f
14 (7 f orbitals)
Maximum
number of
electrons in level
Formula 2n2
n=4 so
4 x 4=16
16x 2=32
n=3
n=2
3d
10 (5 d orbitals)
3p
6 (3 p orbitals)
3s
2 (1 s orbital)
2p
6 (3 p orbitals
18
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Aufbau Principle:
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Orbitals with lower energy are filled before those
with higher energy
Hunds Rule
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Every orbital in a sub level is singly occupied with
electrons of same spin before any one orbital is
doubly occupied
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Electrons fill low energy orbitals (closer to the
nucleus) before they fill higher energy ones.
Where there is a choice between orbitals of
equal energy, they fill the orbitals singly as far
as possible.
The diagram (not to scale) summarises the
energies of the orbitals up to the 4p level.
http://www.chemguide.co.uk/atoms/propert
ies/3d4sproblem.html
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Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus. Some
characteristics of alpha radiation are:
•Most alpha radiation is not able to penetrate human skin.
•Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or
absorbed through open wounds.
•A variety of instruments has been designed to measure alpha radiation. Special training in the use of
these instruments is essential for making accurate measurements.
•A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.
•Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or other
material, because alpha radiation is not penetrating.
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•Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard.
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•Alpha radiation is not able to penetrate clothing.
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Examples of some alpha emitters: radium, radon, uranium, thorium.
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Beta radiation is a light, short-range particle and is actually an ejected electron. Some
characteristics of beta radiation are:
•Beta radiation may travel several feet in air and is moderately penetrating.
•Beta radiation can penetrate human skin to the "germinal layer," where new skin cells
are produced. If high levels of beta-emitting contaminants are allowed to remain on the
skin for a prolonged period of time, they may cause skin injury.
•Beta-emitting contaminants may be harmful if deposited internally.
•Most beta emitters can be detected with a survey instrument and a thin-window GM
probe (e.g., "pancake" type). Some beta emitters, however, produce very low-energy,
poorly penetrating radiation that may be difficult or impossible to detect. Examples of
these difficult-to-detect beta emitters are hydrogen-3 (tritium), carbon-14, and sulfur-35.
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•Clothing provides some protection against beta radiation.
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Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35.
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.Gamma and X Radiation
Gamma radiation and x rays are highly penetrating electromagnetic radiation.
Some characteristics of these radiations are:
•Gamma radiation or x rays are able to travel many feet in air and many inches in
human tissue. They readily penetrate most materials and are sometimes called
"penetrating" radiation.
•X rays are like gamma rays. X rays, too, are penetrating radiation. Sealed
radioactive sources and machines that emit gamma radiation and x rays
respectively constitute mainly an external hazard to humans.
•Gamma radiation and x rays are electromagnetic radiation like visible light,
radiowaves, and ultraviolet light. These electromagnetic radiations differ only in
the amount of energy they have. Gamma rays and x rays are the most energetic of
these.
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•Dense materials are needed for shielding from gamma
radiation. Clothing provides little shielding from
penetrating radiation, but will prevent contamination of the
skin by gamma-emitting radioactive materials.
•Gamma radiation is easily detected by survey meters with
a sodium iodide detector probe.
•Gamma radiation and/or characteristic x rays frequently
accompany the emission of alpha and beta radiation during
radioactive decay.
Examples of some gamma emitters: iodine-131, cesium-137,
cobalt-60, radium-226, and technetium-99m.