Download Unit 4 Chap. 4 Arrangement of Electrons in Atoms

1
Chemistry Lecture ’93 B.Rife CHS
Text: Modern Chemistry; Holt, Rinehart & Winston 1993
page 1/8
Arrangement of Electrons in Atoms Chapter 4
Homework:
1
Section Reviews
(pg 108,111,121)
2
Reviewing Concepts
(pg 122-124)
(3,4,5,8,10,12,14,16,17-21,23-26,29,31,33-35)
3
Problems (all) (pg 124)
4
Chapter/Section Review (Handout)
Due Date
Exam Date _
4.1 Refinements of the Atomic Model
4.1A Discuss the dual wave-particle nature of light
(4)
ELECTRONS HAVE WAVE-PARTICLE DUALITY, WHICH IS THE PHENOMENON WHEREIN PARTICLES
DEMONSTRATE THE PROPERTIES OF WAVES, AND WAVES DEMONSTRATE THE PROPERTIES
OF PARTICLES.
SPECTROSCOPY - THE METHODS FOR STUDYING SUBSTANCES THAT ARE EXPOSED TO SOME
SORT OF CONTINUOUS ENERGY.
ELECTROMAGNETIC RADIATION - ELECTROMAGNETIC RADIATIONS ARE FORMS OF ENERGY
THAT TRAVEL THROUGH SPACE AS WAVES.
- ENERGY THAT IS PROPAGATED BY MEANS OF ELECTRIC AND MAGNETIC FIELDS THAT
OSCILLATE IN DIRECTIONS PERPENDICULAR TO THE DIRECTION OF TRAVEL OF THE
ENERGY.
EXAMPLES: RADIO WAVES- VISIBLE LIGHT - GAMMA RAYS
FREQUENCY (f) - THE NUMBER OF REPEATING CORRESPONDING POINTS ON A WAVE THAT PASS A
GIVEN OBSERVATION POINT PER UNIT TIME.
- THE NUMBER OF CYCLES PER UNIT OF TIME.
HERTZ (Hz) - THE FREQUENCY UNIT, IS ONE CYCLE PER SECOND.
WAVELENGTH - THE DISTANCE BETWEEN TWO CORRESPONDING POINTS OF A WAVE
AND IS REPRESENTED BY LAMBDA ( )
AMPLITUDE OF A WAVE IS ITS MAXIMUM DISPLACEMENT FROM A BASE LINE.
4.1B Explain the mathematical relationship among the velocity, wavelength, and frequency of
electromagnetic radiation(4)
EM RADIATION MOVES AT THE SPEED OF LIGHT, 3.0 x 108 m/s.
FOR EM RADIATION c =
c IS THE SPEED OF LIGHTf
IS THE FREQUENCY
IS THE WAVELENGTH
2
4.1C Discuss the significance of the line emission spectrum of hydrogen to the model of atomic
structure(5)
SPECTRA OF ATOMS
WHEN AN ELECTRIC CURRENT IS PASSED THROUGH A GAS IN A VACUUM TUBE AT VERY LOW
PRESSURES, THE GAS EMITS LIGHT THAT CAN BE SEPARATED BY A PRISM INTO DISTINCT LINES.
SUCH A SPECTRUM IS CALLED AN EMISSION SPECTRUM TO INDICATE THE ORIGIN OF ITS
LIGHT. ITS ALSO CALLED A LINE SPECTRUM TO DESCRIBE ITS APPEARANCE.
THE CERTAIN LINES IN A SPECTRUM INDICATES ONLY CERTAIN WAVELENGTHS ARE BEING
EMITTED
WHEN LIGHT IS PASSED THROUGH A GAS, THE GAS WILL ABSORB CERTAIN WAVELENGTHS OF
LIGHT. THIS IS KNOWN AS THE ABSORPTION SPECTRUM.
PHOTOELECTRIC EFFECT - THE EMISSION OF ELECTRONS BY A SUBSTANCE WHEN ILLUMINATED
BY ELECTROMAGNETIC RADIATION.
EINSTEIN RECEIVED THE NOBEL PRIZE IN 1921 FOR HIS EXPLANATION OF THE
PHOTOELECTRIC EFFECT, NOT FOR HIS THEORY OF RELATIVITY.
RADIATION IS NOT CONTINUOUS BUT CONSISTS OF INDIVIDUAL BUNDLES OF ENERGY CALLED
PHOTONS THAT HAVE PARTICLE LIKE PROPERTIES.
PHOTONS - A "PACKET" OF LIGHT OR ELECTROMAGNETIC RADIATION;
ALSO CALLED A QUANTUM OF LIGHT.
THE ENERGY OF PHOTONS IS PROPORTIONAL TO THE FREQUENCY OF RADIATION BY E = hf
E IS THE ENERGY OF THE PHOTON
f IS THE FREQUENCY OF THE RADIATION
h IS A PROPORTIONALITY CONSTANT CALLED
PLANCK'S CONSTANT
PLANCK'S CONSTANT (h) = 6.6262 x 10-34 J/Hz
WHEN ATOMS OR MOLECULES ABSORB OR EMIT RADIATION AS THEY CHANGE
THEIR ENERGIES, THE FREQUENCY OF THE LIGHT IS RELATED TO THE ENERGY
CHANGE BY THE EQUATION: E = hf
AN ATOM THAT HAS ABSORBED ENERGY IN THIS WAY IS IN AN EXCITED STATE.
THE MOST STABLE STATE OF AN ATOM, THE LOWEST ENERGY STATE OF AN ELECTRON IN AN
ATOM, IS CALLED ITS GROUND STATE ELECTRON CONFIGURATION.
IN THIS CONDITION THE ELECTRONS HAVE THE LOWEST POSSIBLE ENERGIES.
AS AN ELECTRON MOVES FARTHER FROM THE NUCLEUS IN FIXED ENERGY ORBITALS, IT ABSORBS
QUANTIZED ENERGY.
3
ELECTRONS ABSORB OR EMIT (LIGHT) ONLY WHOLE NUMBERS OF QUANTA.
EACH WAVELENGTH CORRESPONDS TO A DEFINITE CHANGE IN THE ENERGY OF THE ELECTRON.
(LYMAN, BALMER SERIES)
4.1D Describe the Bohr model of the hydrogen atom(2)
IN 1913, NEILS BOHR, A DANISH PHYSICIST, PROVIDED AN EXPLANATION FOR THE OCCURRENCE
OF LINE SPECTRA. APPLYING PLANCK'S IDEAS ABOUT QUANTIZATION OF RADIANT ENERGY,
BOHR SUGGESTED THAT THE ELECTRONS IN AN ATOM REVOLVE AROUND THE NUCLEUS OF AN
ATOM ONLY IN CERTAIN DISCRETE ORBITS, WITH NO OTHER ORBITS BEING POSSIBLE.
(PLANETARY MODEL)
THIS MEANS THAT AN ELECTRON COULD HAVE ONLY CERTAIN ENERGIES (COULD
OCCUPY ONLY CERTAIN ENERGY LEVELS), AND MUST ABSORB OR EMIT ENERGY IN
DISCRETE AMOUNTS AS IT MOVES FROM ONE ALLOWED ENERGY LEVEL (ORBIT) TO
ANOTHER.
WHEN AN ELECTRON FALLS BACK TO ITS ORIGINAL ENERGY LEVEL FROM AN EXCITED ONE, IT
EMITS A QUANTIZED AMOUNT OF ENERGY IN THE FORM OF LIGHT.(QUANTUM THEORY)
4.1E Distinguish between an orbit and an orbital(5)
ATOMIC ORBITAL - MEANS A REGION IN SPACE IN WHICH THE PROBABILITY OF FINDING AN
ELECTRON IS LARGE.
4.2 Quantum Numbers and Atomic Orbitals
NEWTONIAN MECHANICS - CLASSICAL MECHANICS DESCRIBES THE BEHAVIOR OF VISIBLE
OBJECTS TRAVELING AT ORDINARY VELOCITIES (NO WAVELENGTH)
QUANTUM MECHANICS - DESCRIBES THE BEHAVIOR OF EXTREMELY SMALL PARTICLES TRAVELING
AT VELOCITIES NEAR THE SPEED OF LIGHT (WAVELENGTHS)
ONE OF THE UNDERLYING PRINCIPLES OF QUANTUM MECHANICS IS THAT WE CANNOT DETERMINE
PRECISELY THE PATHS THAT ELECTRONS FOLLOW AS THEY ORBIT ATOMIC NUCLEI.
THE HEISENBERG UNCERTAINTY PRINCIPLE (1927) STATES THAT IT IS IMPOSSIBLE TO DETERMINE
ACCURATELY BOTH THE MOMENTUM AND THE POSITION OF AN ELECTRON (OR ANY OTHER
SMALL PARTICLE) SIMULTANEOUSLY.
THE PHOTON USED TO LOCATE THE ELECTRON WILL CHANGE THE VELOCITY OF
THE ELECTRON AS A RESULT OF THE COLLISION.
BUT INSTEAD PROBABLE LOCATIONS OF ELECTRONS (ORBITALS) ARE DETERMINED USING
STATISTICS. (probability)
THE POSITION OF AN ELECTRON CAN BEST BE REPRESENTED BY AN ELECTRON CLOUD.
ONE ATOM IS NOT ABLE TO PENETRATE THE SPACE OF A SECOND ATOM BECAUSE OF THE
ELECTRON CLOUD.
4
THE TREATMENT OF THE ELECTRON AS A WAVE PRODUCED A MATHEMATICAL EXPRESSION THAT
CAN BE USED TO DETERMINE THE PROBABILITY OF FINDING AN ELECTRON AT A POINT IN SPACE.
THIS EXPRESSION IS THE SCHRODINGER WAVE EQUATION.
THE SOLUTION OF THE SCHRODINGER-DIRAC EQUATIONS FOR HYDROGEN ATOMS GIVE FOUR
QUANTUM NUMBERS THAT DESCRIBE THE VARIOUS STATES AVAILABLE TO HYDROGEN'S SINGLE
ELECTRON.
WE CAN USE THESE QUANTUM NUMBERS TO DESCRIBE THE ELECTRONIC (ELECTRON)
ARRANGEMENTS IN ALL ATOMS, THEIR ELECTRONIC CONFIGURATIONS.
4.2A List the four quantum numbers and describe their significance.(4)
THE FIRST QUANTUM NUMBER, THE PRINCIPLE QUANTUM NUMBER (n)
DESCRIBES THE MAIN ENERGY LEVEL AN ELECTRON OCCUPIES.
IT MAY TAKE ANY POSITIVE INTEGRAL VALUE: n = 1, 2, 3, 4....
IN GENERAL, THE SIZE OF THE CHARGE CLOUD VARIES WITH THE PRINCIPLE QUANTUM NUMBER
(n)
ELECTRONS IN THE FIRST ENERGY LEVEL HAVE THE LOWEST ENERGIES. (RELATIVE
TO HIGHER ENERGY LEVELS)
4.2B Explain the number of sublevels corresponding to each of the main energy levels, the number of
orbitals per sublevel, and number of orbitals per main energy level.(5)
ENERGY SUBLEVELS AND ORBITALS
THE SECOND QUANTUM NUMBER, THE ORBITAL QUANTUM NUMBER (l) SPECIFIES SUBLEVELS
WITHIN THE MAIN ENERGY LEVELS.
EACH SUBLEVEL HAS A GEOMETRIC SHAPE.
l = 0 = s SUBLEVEL (SPHERICAL SHAPE)
= 1 = p SUBLEVEL (DUMBBELL SHAPE)
(HIGHER ENERGY THAN s SUBLEVEL)
= 2 = d SUBLEVEL
= 3 = f SUBLEVEL
THE LETTERS s, p, d, and f STAND FOR SHARP, PRINCIPAL, DIFFUSE, AND FUNDAMENTAL.
THESE TERMS WERE ORIGINALLY SPECTROSCOPY LABELS FOR DIFFERENT SERIES OF
SPECTRAL LINES EMITTED BY THE ELEMENTS.
THE SPACE OCCUPIED BY ONE PAIR OF ELECTRONS WITHIN A SUBLEVEL IS CALLED AN ORBITAL.
ATOMIC ORBITAL - IS A THREE DIMENSIONAL REGION ABOUT THE NUCLEUS IN WHICH THE
PROBABILITY OF FINDING AN ELECTRON IS LARGE.
5
THE THIRD QUANTUM NUMBER, THE MAGNETIC QUANTUM NUMBER (m ) DESIGNATES THE SPATIAL
ORIENTATION OF A SINGLE ATOMIC ORBITAL.
IF l = 0 = s SUBLEVEL THEN m = 1 POSITION (spherical, fig. 4.14)
= 1 = p SUBLEVEL THEN m = 3 POSITIONS (x, y, & z, FIG 4.15)
= 2 = d SUBLEVEL THEN m = 5 POSITIONS (FIG 4.16)
= 3 = f SUBLEVEL THEN m = 7 POSITIONS
ONE ORBITAL (TWO ELECTRONS) FIT IN ONE POSITION
DEGENERATE ORBITALS (ORBITALS WITHIN A SUBLEVEL) ARE OCCUPIED BY ELECTRONS HAVING
THE SAME ENERGY.
4.2C Discuss the significance of the spin quantum number (2)
THE FOURTH QUANTUM NUMBER, THE SPIN QUANTUM NUMBER (ms) REFERS TO THE SPIN OF AN
ELECTRON AND THE ORIENTATION OF THE MAGNETIC FIELD PRODUCED BY THE SPIN OF
THE ELECTRON.
ms CAN TAKE THE VALUES OF +1/2 (CLOCKWISE) OR
-1/2 (COUNTERCLOCKWISE).
ELECTRONS OF OPPOSITE SPIN IN THE SAME ORBITAL WOULD HAVE APPROXIMATELY THE SAME
ENERGIES.
DIAMAGNETISM IS THE PROPERTY OF A SUBSTANCE WHEREBY IT IS WEAKLY REPELLED BY A
MAGNETIC FIELD.
PARAMAGNETISM IS A WEAK ATTRACTION BETWEEN MAGNETIC FIELDS AND SUBSTANCES WHOSE
ATOMS HAVE AN UNEVEN ELECTRON DISTRIBUTION(OXYGEN, FERROMAGNETISM)
6
ENERGY LEVELS AND ORBITALS
n
l
DESIGNATION
(SUBLEVELS)
# OF
ORBITALS
# OF
ELECTRONS
1
0
1s
1
2
2
0
2s
1
2
1
1
1
2px
2py
2pz
3 EQUIVALENT
2
2
2
0
3s
1
2
1
1
1
3px
3py
3pz
3 EQUIVALENT
2
2
2
2
2
2
2
2
3d
3d
3d
3d
3d
5 EQUIVALENT
2
2
2
2
2
3
2 TOTAL
8 TOTAL
18 TOTAL
4.2D List total number of electrons needed to fully occupy each main-energy level
(3)
MAXIMUM NUMBER OF ELECTRONS IN ENERGY LEVEL = 2n2 (n = PRINCIPAL QUANTUM NUMBER)
4.3 Electron Configurations
4.3A State the Aufbau principle, Hund’s rule, and the Pauli exclusion principle(5)
THE PAULI EXCLUSION PRINCIPLE (1940) STATES THAT NO TWO ELECTRONS IN AN ATOM MAY
HAVE IDENTICAL SETS OF ALL FOUR QUANTUM NUMBERS.
THE IMAGINARY PROCEDURE OF BUILDING UP THE ELECTRONIC CONFIGURATIONS ONE ELECTRON
AT A TIME IS OFTEN REFERRED TO AS THE "AUFBAU" PROCESS.
THE AUFBAU PRINCIPLE STATES THAT THE ELECTRON THAT DIFFERENTIATES AN ELEMENT FROM
THE PRECEDING ELEMENT (LAST ELECTRON ADDED) ENTERS THE AVAILABLE ATOMIC
ORBITAL OF LOWEST ENERGY.
THE ORDER OF INCREASING ORBITAL ENERGIES FOR THE FIRST SIX PERIODS ARE:
1s; 2s,2p; 3s, 3p; 4s, 3d, 4p; 5s, 4d, 5p; 6s, 4f, 5d, 6p, 7s, 5f, 6d
7
DIAGONAL RULE
1
2
3
1s
2s
2p
3s
3p
4s
4
3d
4p
5s
5
6 period
4d
5p
6s
4f
5d
6p
7s
5f
6d
7p
8s
HUND'S RULE: ELECTRONS OCCUPY ALL THE ORBITALS
OF A GIVEN SUBLEVEL SINGLY BEFORE PAIRING
BEGINS.
4.3B Describe the arrangement of electrons around the atoms of any element using orbital
notation, electron-configuration, notation or electron-dot notation(12)
TO REPRESENT ELECTRONIC STRUCTURES SEVERAL NOTATIONS ARE USED:
ORBITAL NOTATION:
___ NO ELECTRONS IN ORBITAL
H
___ ONE ELECTRON IN ORBITAL
He
___ TWO ELECTRONS IN ORBITAL
ELECTRON-CONFIGURATION NOTATION
1s1
ONE ELECTRON IN ORBITAL (H)
1s2
TWO ELECTRONS IN ORBITAL (He)
1s22s1 Li
1s22s2 Be
1s22s22p1 B
THE ATOMIC NUMBER (Z) IS EQUAL TO THE TOTAL NUMBER OF THE SUPERSCRIPTS IN THE
ELECTRON CONFIGURATION.
ELECTRON DOT DIAGRAMS
USUALLY ONLY THE ELECTRONS IN THE OUTER LEVEL OF ATOMS ARE INVOLVED IN CHEMICAL
CHANGE.
IN THE ELECTRON DOT DIAGRAM, THE SYMBOL REPRESENTS THE NUCLEUS AND ALL ELECTRONS
EXCEPT THOSE IN THE OUTER LEVEL.
IN THE ELECTRON DOT DIAGRAM, DOTS INDICATE OUTER LEVEL PAIRED OR UNPAIRED
ELECTRONS.
ELECTRON-DOT NOTATION (LEWIS DOT FORMULAS)
8
H
ONE ELECTRON IN ORBITAL
He
TWO ELECTRONS IN ORBITAL
63
4
py 7
px
2
1 s
58
EXAMPLE OXYGEN (Z = 8)
O
pz
4.3C Build up the electron configuration for atoms of any
identity of the element
(12)
Al 1s22s22p13s23p1
element, given the atomic number or
[Ne] 3s23p1
Z = 46 ---> Pd [Kr] 5s24d8
4.3D Describe the noble-gas configuration and write it for any noble gas(3)
A NOBLE GAS CONFIGURATION IS AN OUTER MAIN ENERGY LEVEL OCCUPIED, IN MOST CASES, BY
EIGHT ELECTRONS
ns2np6 n = PRINCIPAL QUANTUM NUMBER Xe 5s25p6