Transcript Atomic Structure: Atoms and Ions

Atomic Structure: Atoms and
Ions
Unit Objectives:
1. trace the development of models of the atom
2. show that atomic theory is consistent with experimental
observations
3. describe the properties of atoms and subatomic particles
4. explain the relationship between emission spectra and
atomic structure
5. explain the use of wave-mechanics in atomic theory
6. describe the wave-mechanical model of the atom
7. locate electrons in energy levels, sublevels, and orbitals
8. make orbital diagrams and write electron configurations
for elements with atomic numbers from 1 through 38
Created by C. Ippolito
October 2005
Crooke’s Tube
• William Crookes
• studies matter in vacuum tubes with
metal plates
• Cathode Plate
• accumulated negative charge
• Anode Plate
• accumulated positive charge
• notices green glow in shape of
anode
• moves from cathode to anode
• Cathode Rays
Created by C. Ippolito
October 2005
Electron
• J J Thompson
• cathode rays made of negative
particles
• electrons
• one unit of negative charge
• Robert Millikan
• Oil Drop Experiment
• transferred electrons to oil drop
• dropped through two plates
• varying voltage showed that was
always a multiple of one small
charge
• calculate mass as 1/1837 the mass
of lightest element H
Created by C. Ippolito
October 2005
Proton
• Eugene Goldstein
• used modified Crooke’s tube
• positive rays traveled towards
cathode
• Wilhelm Wien
• measured charge on proton
• JJ Thomson
• charge equal but opposite of
electron
• calculated mass as 1837x that of
electron
Created by C. Ippolito
October 2005
Neutron
• Ernest Rutherford
• proposed the existence of a
third neutral particle
• James Chadwick
• established existence of particle
with same mass as proton but
no charge
• neutron
Created by C. Ippolito
October 2005
Plum Pudding Model
• J J Thomson
• Felt that the atom was
composed of mostly
positive “stuff” with small
piece of negative charge
mixed throughout
Created by C. Ippolito
October 2005
X-Rays and Radioactivity
• Wilhelm Roentgen
• discovered X-rays
• Antoine Becquerel
• studied fluorescence
• noticed uranium exposed photographic plates
• Marie Curie
• studies this phenomena and calls it radiation
Created by C. Ippolito
October 2005
Types of Radiation
• Alpha () Rays
• have a double positive charge
• mass of 4 amu
• Beta (β) Rays
• same as cathode rays
• negative charge – stream of electrons
• Gamma () Rays
• not affected by magnetic field
• like x-rays
Created by C. Ippolito
October 2005
Rutherford’s Nuclear Model
• shot  particles at gold foil
• most particles went through foil
• some deflected
• very few bounced back
• Nuclear Model
• atom mostly empty space
• small very dense area has all of mass and is
positively charged
• this area is the NUCLEUS
• a.k.a. Solar System Model of the Atom
Created by C. Ippolito
October 2005
Spectroscopy
• studies the behavior of substances exposed
to a continuous exciting energy
• elements release absorbed energy as light
• LIGHT
• electromagnetic energy in the form of a wave
• Frequency (f) cycles/second hertz
• Wavelength (lambda = λ) nanometers
• Amplitude height of peaks and troughs
• velocity = f λ for light velocity = c (3.0 x 108 m/s)
Created by C. Ippolito
October 2005
Line Spectra
• unique set of light wavelengths released by
excited substance returning to ground
state
• sodium (Na+)
• potassium (K+)
• barium (Ba+2)
• strontium (Sr+2)
• lithium (Li+1)
Created by C. Ippolito
October 2005
Wave (Quantum) Mechanics
• studies the motion of relatively small particles
that travel at relatively fast speeds
• Max Planck
• light energy not released continuously
• released in small spurts
• quantum – packet of electromagnetic energy
• photon – packet of light energy
• energy is related to frequency of light
• f = c/λ where c = 3.00 x 108 m/s
• E = hf
• h= 6.6 x 10-34 j/hz which is Planck’s constant
Created by C. Ippolito
October 2005
Bohr-Rutherford Model
• Neils Bohr
• used Planck’s idea
• electrons are in energy levels
• ground state – lowest energy level of electron
• excited state – higher energy level of electrons
with absorbed energy
• electrons release absorbed energy as light
when they return to the ground state
• Quantum or Energy Level Model
Created by C. Ippolito
October 2005
De Broglie’s Hypothesis
• combines Einstein’s and Planck’s ideas
• new equation predicts “wave length” of a particle
when mass and velocity are known
• combined Einstein and Planck equations
• E = mc2 and E = hf so that mc2 = hf
• replaced f with v/λ wave frequency is velocity/wavelength
• mv2 = hv/λ
• solves for wavelength
• λ = h/mv
• Wave-Particle Duality of Nature
• waves can act like particles and particles can act like waves
Created by C. Ippolito
October 2005
Measuring Position and
Momentum of the Electron
• Werner Heisenberg
• Heisenberg Uncertainty
Principle
• position and momentum CANNOT
be determined at the same time
• to see object it light reflected to
eyes
• small objects like electron
light bouncing off it changes
its velocity
• never know where an electron
will be or where it is going
Created by C. Ippolito
October 2005
Schrodinger’s Work
• Erwin Schrodinger
• electron a wave
• develops an equation using quantum number
• describes the probable location as an ELECTRON CLOUD
• Four Quantum Numbers
• used to describe electron behavior in complex atoms
Created by C. Ippolito
October 2005
Principle Quantum Number (n)
• describes energy
levels
• used find maximum
number of electrons
• 2n2 = maximum
electrons on level
• n2 = number of
orbitals
#
n2
Orbitals
2n2
# of e-
1
(1)2
1
2(1)2
2
2
(2)2
4
2(2)2
8
3
(3)2
9
2(3)2
18
4
(4)2
16
2(4)2
32
Created by C. Ippolito
October 2005
Second Quantum Number (l)
• complex atoms with more than one
level have higher level divided into
sublevels
•
•
•
•
s – lowest sublevel – “sharp”
p – second sublevel – “principal”
d – third sublevel – “diffuse”
f – fourth sublevel –”fundamental”
Created by C. Ippolito
October 2005
Third Quantum Number (m)
• represents subdivisions in the sublevels
– orbitals
•
•
•
•
s – one electron pair
p – three electron pairs
d – five electron pairs
f – seven electron pairs
Created by C. Ippolito
October 2005
Distribution of Electrons
• Pauli’s Exclusion Principle
• no two electrons can have exactly the
same quantum numbers
• Fourth Quantum Number
• describes magnetic spin
• Hund’s Rule
• electrons prefer to occupy an empty orbital
before it will occupy one as a pair
Created by C. Ippolito
October 2005
Diagonal Rule
• atoms with high
atomic numbers
do not fill
orbitals in order
Created by C. Ippolito
October 2005
Electron Dot Diagrams
• chemical properties depend on valance
(outermost) electrons
• element symbol represents nucleus and all
lower level electrons
• write out electron configuration
• draw dots on sides to represent electrons
in orbitals (basically last level of Bohr
diagram)
Created by C. Ippolito
October 2005
Electron Configuration
Samples
•
•
•
•
•
H – 1s1
He – 1s2
O – 1s2 2s2 2p4
Ca – 1s2 2s2 2p6 3s2 3p6 4s2
Cd - 1s2 2s2 2p6 3s2 3p6 4s2 3d10
4p6 5s2 4d10
Created by C. Ippolito
October 2005