Download §2 Atomic Structure , A website that gives a good summary of this

§2 Atomic Structure
,
A website that gives a good summary of this section can be found at ... Atomic Properties
2.1 The Atom:
Assessment Statement
2.1.1 State the positions of protons,
neutrons
and electrons in the atom.
2.1.2 State the relative masses and
relative
charges of protons, neutrons and
electrons.
2.1.3 Define the terms mass number (A),
atomic number (Z) and isotopes of
an
element.
2.1.4 Deduce the symbol for an isotope
given
its mass number and
atomic number.
2.1.5 Calculate the number of protons,
neutrons and electrons in atoms
and
ions from the mass number, atomic
number and charge.
2.1.6 Compare the properties of the
isotopes
of an element.
2.1.7 Discuss the use of radioisotopes
Teaching notes
1 TOK: None of these particles can be (or will be)
directly
observed. Which ways of knowing do we use to
interpret
indirect evidence gained through the use of
technology?
Do we believe or know of their existence?
1 The accepted values are:
relative mass
relative charge
proton:
1
+1
neutron
1
0
electron
5 × 10-4
–1
1
Obj.
3
The following notation should be used:
a
zX,
eg. 126C
2
3
3
Examples should include 14C in radiocarbon
dating, 60Co in
radiotherapy, and 131I and 125I as medical tracers.
From the very early thought experiments conducted by the ancient Greeks came the idea that matter MUST be co
called "atomus" or atoms
Rutherford, investigating the nature of these small particles, constructed a model of the atom that places positive
held in place by some kind of nuclear "glue" - we know now the neutral neutrons perform this service. Surroundi
variously as shells or orbits or even more correctly orbitals. The proposed structure of these electron orbitals exp
chemical behavior of the elements and which are ultimately reflected in the modern Periodic Table.
Note: The outer shell electrons are called "valence electrons". They are the electrons which are involved in bond
and are referred to as the 'outermost' electrons (keep in mind that does not mean they cannot travel close to the nu
which travel furthest away from the nucleus). Core electrons are electrons that under 'normal' reaction condition
atom which are located in the completely filled energy levels.
Even if the protons and neutrons are miniscule particles occupying the tiny region at the center of the atom The e
only 0.05% of the mass of a proton or neutron! That is 1/5000th the mass of the larger particles.
Atomic number (Z) = no. of protons in an atom's nucleus
Mass number (A) = no. of protons + neutrons in an atom's nucleus
Isotopes are the different possible nuclear configurations for any given element.
Isotopes of an element have the same number of protons (and electrons) but have different numbers of neutrons,
common isotope of carbon, C-12, has 6 protons in its nucleus and also 6 neutrons while the rarer C-14 contains 6
The chemical properties of isotopes are very similar due to the equal numbers of protons and electrons that is they react with other elements etc. in the same way ...
But the physical properties may vary somewhat because of the differing numbers of neutrons these properties include melting and boiling points
2.2 The Mass Spectrometer:
Assessment Statement
2.2.1 Describe and explain the
operation of
a mass spectrometer.
2.2.2 Describe how the mass
spectrometer
may be used to determine
relative
atomic mass using the 12C scale.
2.2.3 Calculate non-integer relative
atomic
masses and abundance of
isotopes
from given data.
Obj.
Teaching notes
3 A simple diagram of a single beam mass spectrometer
is
required. The following stages of operation should be
considered:
1. vaporization, followed by 2. ionization, then
3.acceleration,
and 4.deflection and finally 5.detection.
Aim 7: Simulations can be used to illustrate the
operation of a
mass spectrometer.
2
2
Know the order of operation of the mass spectrometer ...
vaporisation, ionization, acceleration, deflection
The mass spectrometer measures the relative amounts (%) of the different isotopic masses of a given sample.
For example here a sample of magnesium has been passed thorugh the spectrometer ...
80% of the sample has Z = 24
10% of the sample has Z = 25
10% of the sample has Z = 26
(where RIM = relative isotopic mass)
The RAM (relative atomic mass) of a sample of magnesium is the average mass of the different isotopes that ma
RAM = 0.80 x 24 + 0.10 x 25 + 0.10 x 26
= 24.3
Note that the RAM is closest to the mass number (Z) of the most abundant isotope.
2.3 Electron Arrangement:
Assessment Statement
2.3.1
Describe the electromagnetic
spectrum.
Obj.
2
Teaching notes
Students should be able to identify the
ultraviolet, visible and infrared regions,
and to describe the variation in
wavelength, frequency and energy across
the spectrum.
TOK: Infrared and ultraviolet spectroscopy
are dependent on technology for their
existence. What are the knowledge
implications of this?
2.3.2
2.3.3
2.3.4
Distinguish between a
continuous spectrum and a
line spectrum.
Explain how the lines in the
emission spectrum of
hydrogen are related to
electron energy levels.
Deduce the electron
arrangement for atoms and
ions up to Z=20
2
3
3
Students should be able to draw an
energy level diagram, show transitions
between different energy levels and
recognize that the lines in a line spectrum
are directly related to these differences.
An understanding of convergence is
expected. Series should be considered in
the ultraviolet, visible and infrared
regions of the spectrum.
Calculations, knowledge of quantum
numbers and historical references will not
be assessed.
Aim 7: Interactive simulations modeling
the behavior of electrons in the hydrogen
atom can be used.
For example, 2.8.7 or 2,8,7 for Z = 17.
TOK: In drawing an atom, we have an image of an invisible
world. Which ways of knowing allow us access to the microscopic world?
The EM spectrum is familiar to us as the colors of the rainbow. This, however, is only a very small part of the co
investigated the spectra emitted by various element, especially hydrogen.
Here we see two spectra from hydrogen. The first is the absorption spectrum and is formed when white light pass
energy required to boost electrons in the electron clouds of the hydrogen atoms to higher levels; energy is absorb
black lines appear where this energy once was. The second spectra is caused when the energy absorbed by the ele
their original energy levels.
There are many of these spectral lines not only in the visible part of the EM spectrum but also in the UV and IR p
These are called the Lyman series, Balmer series, Paschen series etc.
Consideration of these spectral lines in the spectra of many of the elements led eventually to the idea of the electr
advanced form based on Rutherford's original model and proposed by the Dane Niels Bohr.
To the right we see an energy level diagram, the arrows show the transitions of electrons already boosted by abso
Level n = 1 is the so-called lowest energy level while level n = inf represents complete escape from the nucleus's
Note the importance of this piece of evidence. It implies that there are particular energy values that the electrons
associate with the electron shells. Electrons CANNOT exist in between these particular values. This was realized
Quantum Theory. He modified the Rutherford model of the atom to what we still use today.
Bohr's model proposes that electron energy levels that surround the nucleus exist as several sublevels.



Each level contains a number of sublevels called s, p, d, f.
At each sublevel there are 1, 3, 5, 7 orbitals which can contain a maximum 2 electrons according to the P
Note the neat mathematical relationships involved in the model for each level n, the thotal number of electrons is 2n2,
for each sublevel m there are 2m-1 orbitals where s=1, p=2, d=3, f=4
and finally there are a maximum of 2 electrons allowed in each orbital
Thus we can start to describe the electron configurations of elements ...
Hydrogen, H : 1s1
Helium, He : 1s2
and now the 1st energy level containing 1 s orbital is full
Lithium, Li :
1s2, 2s1
Beryllium, Be : 1s2, 2s2
and now the 1st and 2nd energy levels' "s" orbitals are full, we continue wit
Boron, B :
Carbon, C :
Nitrogen, N :
Oxygen, O :
Fluorine, F :
Neon, Ne :
1s2, 2s2, 2p1
1s2, 2s2, 2p2
1s2, 2s2, 2p3
1s2, 2s2, 2p4
1s2, 2s2, 2p5
1s2, 2s2, 2p6
and now the 2nd energy level is full, we continue to fill the 3rd level etc.
Sodium, Na :
1s2, 2s2, 2p6, 3s1
Magnesium, Mg: 1s2, 2s2, 2p6, 3s1
Aluminum, Al :
Silicon, Si :
Phosphorus, P :
Sulfur, S :
Chlorine, Cl :
Argon, Ar :
1s2, 2s2, 2p6, 3s2, 3p1
1s2, 2s2, 2p6, 3s2, 3p2
1s2, 2s2, 2p6, 3s2, 3p3
1s2, 2s2, 2p6, 3s2, 3p4
1s2, 2s2, 2p6, 3s2, 3p5
1s2, 2s2, 2p6, 3s2, 3p6
Now that the 3p shells are full (3x2=6) you might expect that the next level
some reason the 4s shell involves less energy than the 3d so it fills first! It must be noted that
argue against this fact. We must accept it and incorporate it into our model of the electron structure of
attachment below for a neat way of describing the increasing energy levels of the enegy
Potassium, K :
Calcium, Ca :
1s2, 2s2, 2p6, 3s2, 3p6, 4s1
1s2, 2s2, 2p6, 3s2, 3p6, 4s2
and here the filling of the 4th shell takes a break while the 3d shell fills
Scandium, Sc :
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d1
... there are 5 possible d orbitals which accommodate 10 possible electrons, he
metals which fit into the Periodic Table between calcium and gallium.
The last of these is ...
Zinc, Zn :
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10
and now the 3rd level is full at last we continue filling the 4p energy levels
Gallium, Ga :
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p1
The order in which the orbitals fill with electrons is quite ordered but the order is not quite as straight forward as
By following the blue arrows down and to the left this diagram shows clearly how the 4s orbital has lower energy
the transition metals that "appear" between the s-block and p-block in the Periodic Table.
Note that for SL you do not need to know this more complicated system involving s, p, d and f orbitals as shown
the right - see the syllabus point 2.3.4 above. However knowledge of this system enables us to understand the sha
topic
Here are the basic s, p, d and f orbital shapes ...
There are of course 3 p-orbitals, 5 d-orbitals and 7 f-orbitals which make the actual zone around the atom quite c
the HL web site.