Download Atomic Theory - Sardis Secondary

2014-­‐05-­‐06 The Atom
—  The concept of a discrete unit that makes up all
Atomic Theory
Chemistry 11
matter has been around for centuries.
—  These ideas were based on philosophical reasoning
rather than experimentation and empirical
observations.
—  This concept has been accepted by scientists since
it elegantly explains new discoveries in the field of
chemistry.
In addition…
—  Aristotle proposed that all matter
is made up of 4 elements with 4
different properties:
The fifth element is
Aether, the
material that fills
the region of the
universe above the
terrestrial sphere.
Atomic Number and Atomic Mass
—  The elements are differentiated from one
another by the numbers of protons in the
nucleus.
—  Atomic Number:
—  The number of protons in the nucleus.
—  A neutral atom has no charge, therefore:
In a neutral atom:
Number of Protons = Number of Electrons
—  For Example:
How many electrons are possessed by the following?
N3-
10 electrons
Ca2+
18 electrons
Br-
36 electrons
1 2014-­‐05-­‐06 —  Since both neutrons and protons have a mass of
1.0 u, the total atomic mass of an atom will be
found by their combined totals.
—  For Example:
—  Find the number of protons, neutrons, and electrons
possessed by the following:
What about the
electrons?
—  Species having the same atomic number, but different
atomic masses (same # of protons, different number
of neutrons).
1
1
H
= ORDINARY HYDROGEN (called “protium”).
2
1
H = DEUTERIUM (sometimes call “heavy” hydrogen).
3
1
H = TRITIUM (called “radioactive” hydrogen).
13 protons, 14 neutrons, 13 electrons
75
33
As
33 protons, 42 neutrons, 33 electrons
—  For Example:
Experiments show that chlorine is a mixture which
is 75.77% Cl-35, and 24.23% Cl-37. If the precise
molar mass of Cl-35 is 34.968853 g/mol and of
Cl-37 is 36.965903 g/mol, what is the average
molar mass of the chlorine atoms in such a
mixture?
Homework:
—  You may also use the atomic mass to calculate the
average. The average mass will be less exact, but
still satisfactory.
Al
The molar masses given on the periodic
table are found by calculating the
average mass of a sample containing a
mixture of isotopes.
—  Isotope:
For Example:
27
13
—  Do:
—  Introduction to Atomic Theory W.S.
2 2014-­‐05-­‐06 The Periodic Table!
—  As real elements became
discovered, the Greek ideas of
Air, Earth, Fire, and Water
had to be abandoned.
—  Scientists needed an elegant, easy to use method
of accessing all the information about the
elements.
Major Divisions Within the
Periodic Table
—  Two important trends appear in the periodic table:
—  Period:
The set of elements in a given row going
across the table.
—  Group or Family:
The set of elements in a given column going
up and down the table.
—  There are several groups, rows, and “blocks” of
elements:
In summary:
3 2014-­‐05-­‐06 —  In 1913, Niels Bohr proposed a model that
The Electronic Structure of the Atom
—  When a hydrogen atom is irradiated by
energy, some of the energy is absorbed
then reemitted as light.
explained why the observed line spectrum for
Hydrogen looks the way it does.
—  He proposed that:
—  The electron in hydrogen can only exist
—  If the light is passed through a prism, a “line
in specific energy states. These energy
states are associated with specific
circular orbits which the electron can
occupy around the atom.
Listen here, I say! spectrum” is observed.
—  When an electron absorbs energy, it
instantaneously moves from one orbit to
another.
—  The greater the energy, the farther the
orbit is from the nucleus.
—  ENERGY LEVEL:
A specific amount of energy which an electron in an
atom can possess.
—  The energy levels of hydrogen have the pattern
below (“n” is the number of the energy level).
—  The observed spectrum represents energy level
differences occurring when an electron gives off energy
and drops from a higher energy level.
—  The energy difference between two different energy
levels is called the QUANTUM of energy associated with
the transition between the two levels.
The Energy Level Diagram for
Hydrogen
—  The lowest sets of energy levels for hydrogen are as
follows:
—  A few years after Bohr published his theories, several
changes were made to his ideas.
—  The idea of electrons orbiting along a specific path in a
well defined orbit had to be abandoned.
—  Instead, different electrons, depending on their energies,
occupy particular regions of space called “orbitals”.
4 2014-­‐05-­‐06 —  Each dash represents the energy possessed by a
particular orbital in the atom.
—  The letter s, p, d, and f refer to the four “types” of
orbitals (more to come later).
—  Shell:
—  The set of all orbitals having the same n value.
—  For Example:
—  Some notes…
—  All the orbitals for a hydrogen atom with a given value of n
have the same energy (not true for atoms with more than
one electron).
—  Rules governing which types of orbitals can occur:
—  For a given value of “n”, certain types of orbitals are
possible
— 
— 
— 
— 
The 3rd shell consists of the 3s, 3p, and 3d orbitals.
—  Subshell:
—  A set of orbitals of the same type.
—  For Example:
The set of five 3d orbitals in the 3rd shell is a subshell.
— 
— 
— 
— 
For
For
For
For
n=
n=
n=
n=
1:
2:
3:
4:
only the s type is possible
the s and p types are possible
the s, p, and d types are possible
the s, p, d, and f types are possible.
An s type subshell consists of ONE s orbital
A p type subshell consists of THREE p orbitals.
A d type subshell consists of FIVE d orbitals.
An f type subshell consists of SEVEN f orbitals.
The Energy Level Diagram for
Polyelectronic Atoms
—  The energy level diagram must
be modified to describe any
other atom.
—  The following diagram applies
to ALL polyelectronic atoms
(atoms having more than one
electron).
5 2014-­‐05-­‐06 ELECTRON CONFIGURATIONS
—  The addition of electrons to the orbitals follows three simple
rules:
—  Aufbau Principle:
—  As atomic number increases, electrons are added to the available
Writing Electron Configurations for
Neutral Atoms
—  ELECTRON CONFIGERATION:
Describes which orbitals in an atom contain electrons
and how many electrons are in each orbit.
orbitals. To ensure LOWEST POSSIBLE ENERGY for the atom,
electrons are added to the orbitals having the lowest energy FIRST. How do
we do
this?
—  Pauli Exclusion Principle:
—  A maximum of TWO electrons can be placed in each subshell.
—  Hunds Rule:
—  When electrons occupy subshells of equal energy, they must be
singly occupied with electrons having parallel spins. 2nd electrons
are then added to each subshell so each electron has opposite
spin.
Tryski…
Core Notation
—  Predict the electron configuration of the following:
—  Si
1s22s22p63s23p2
—  Tc
1s22s22p63s23p64s23d104p65s24d5
—  Ca
1s22s22p63s23p64s2
—  Zr
1s22s22p63s23p64s23d104p65s24d2
—  Ga
1s22s22p63s23p64s23d104p1
The OUTER electrons are all those outside the
core. Since the core electrons are not involved
in chemical reactions, they are excluded from
the electron configuration.
For Example:
Al 1s22s22p63s23p1
—  The electrons belonging to an atom can be broken
into two subsets:
—  The CORE electrons.
—  The OUTER electrons.
The CORE of an atom is the set of electrons
with the configuration of the nearest noble
gas having an atomic number LESS than that
of the atom being considered.
—  Write the following using core notation:
—  Zr
([Kr]5s24d2)
—  Ga
([Ar]4s23d104p1)
—  Co
([Ar]4s23d7)
becomes:
[Ne]3s23p1
6 2014-­‐05-­‐06 Homework:
—  Do:
Writing Electron Configurations for Ions
—  Anions:
—  The Periodic Table and Stuff W.S. #1-4
Add electrons to the last unfilled subshell, starting
where the neutral atom left off.
For Example:
Oxygen: [He] 2s2 2p4 + 2e- → O2-([He]2s22p6)
Sulphur: [Ne] 3s2 3p4 + 2e- → S-([Ne]3s23p6)
—  For Example:
—  Cations:
—  2 Rules:
1.  Electrons in the outermost shells (largest n value) are
removed first.
2.  If there are electrons in both the s and p orbitals of the
outermost shell, the electrons in the p orbitals are
removed first.
Tin: [Kr] 5s2 4d10 5p2 → 2e- + Sn2+([Kr]5s24d10)
Tin: [Kr] 5s2 4d10 5p2 → 4e- + Sn4+([Kr]4d10)
p electrons BEFORE s electrons BEFORE d electrons
Outermost electrons are removed
preferentially. Also, e- in the highest
energy outermost orbital require the
least amount of energy to be
completely removed from the atom.
I pity the fool
who doesn’t do
these examples!
—  Ru3+
[Kr]4d5
—  Sb3+
[Kr]5s24d10
to Kr:
—  Cr ([Ar] 4s2 3d4) → “3d4” is one e- short of a half
—  S2-
[Ne]3s23p6
—  Cu ([Ar] 4s2 3d9) → “3d9” is one e- short of a filled
—  N3-
[He]2s22p6
—  2 exceptions to the configurations of elements up
filled subshell.
subshell.
7 2014-­‐05-­‐06 —  The actual configurations for Cr and Cu are found
to be:
—  Cr ([Ar] 4s1 3d5) → “4s1” and “3d5” are two half filled
subshells.
—  Cu ([Ar] 4s1 3d10) → “4s1” is a half filled subshell,
and “3d10” is a filled subshell.
—  Because of this extra stability, an atom or ion that
is one e- short of a “d5” or “d10” configuration will
shift an e- from the s- subshell having the highest
energy into the unfilled d- subshell.
—  Therefore:
A filled or exactly half filled
d- subshell is especially stable.
Predicting Number of Valence
Electrons
—  Valence Electrons:
—  Electrons that can take place in chemical reactions.
—  Are all the electrons in the atom EXCEPT:
—  Core electrons.
—  In filled d or f subshells.
—  For Example:
—  Al([Ne] 3s2 3p1) has 3 valence electrons:
→ “3s2 3p1”
—  Ga([Ar] 4s2 3d10 4p1) has 3 valence electrons:
→ Omit “3d10” b/c filled
—  Pb([Xe] 6s2 4f14 5d10 6p2) has 4 valence electrons:
→ Omit “4f14” and “5d10” b/c filled —  Xe([Kr] 5s2 4d10 5p6) has ZERO valence electrons:
→ Noble gas configuration
Homework:
—  Do:
—  The Periodic Table and Stuff W.S. #5-7
—  Study for your quiz!!!
—  Electron Configurations
What is on the Exam?
—  History of the Atom
—  The Atom
—  Atomic Number and Mass
—  # of Protons, Neutrons,
and Electrons
—  Isotopes
—  The Electronic Structure of
the Atoms
—  Theory
—  Configurations (Neutral,
Ions, Core)
—  Exceptions
—  Valence Electrons
—  The Periodic Table
8