Transcript Chapter 7

Chapter 7
Quantum-Mechanical Model
-explains how e- exist in atoms and how close
those e- determine the chemical and physical
properties of elements
-already studied much of this:
-metals vs. non-metals
-noble gases inert
-charges on ions
-electrons and light have much in common
Wave Nature of Light
electromagnetic radiation (waves)- a type of energy
embodied in oscillating electric and magnetic
fields
-waves move at a constant speed of 3.00X108m/s
-this is the speed of light (c)
-takes a particle of light 1/7 of a second to circle
Earth
-this is why you see fireworks before you hear the
bang and why you see lightning before you hear
thunder
-sound travels about 340m/s
origin
electromagnetic waves
amplitude- height of a wave from the origin to
the crest or from origin to trough
-determines the intensity or brightness of the
light, greater amplitude = greater intensity
wavelength- (λ) - distance between two adjacent
crests (units= m, cm, nm)
frequency- (ν) - # of wave cycles that pass
through a given point per unit time
(units= cycles / sec or 1/s or s-1 or hertz- Hz)
-each complete wave cycle begins at the origin
and returns to the origin
-frequency is directly proportional to the speed at
which the wave is traveling- the faster the
wave, the higher the frequency
-frequency and wavelength are inversely
proportional
c = νλ
c = speed of light (3.00 x 108m/s)
ν = frequency (1/s, s-1, Hz)
λ = wavelength (m, cm, nm(10-9))
λ = c/ν
ν = c/λ
page 285 ex 7.1
for practice 7.1
visible light- light that can be seen by the human
eye
-wavelength determines the color of the visible
light
-can see colors when white light is passed
through a prism
-red, orange, yellow, green, blue, indigo, violet
-red light has the longest wavelength (750nm)
-violet has shortest (400nm)
electromagnetic spectrum- includes all
wavelengths of electromagnetic radiation
(radio, microwaves, infrared, visible, UV rays,
X-rays, and gamma rays)
page 285 figure 7.5
left side = low energy, low frequency, long
wavelength
right side = high energy, high frequency, short
wavelength
Types of electromagnetic radiation:
radio waves- longest wavelengths, 105, transmits
signals for radios, cell phones, TV
microwaves- used for radar and microwaves
infrared radiation (IR)- the heat you feel when
you place your hand near a hot object
visible light- light you can see
UV rays- from the sun
X-rays- used to image bones and internal organs
gamma rays (γ)- produced by the sun or in
space, very dangerous because of high energy
interference- waves can cancel each other out or
build each other up
-depends on alignment upon interaction
-if waves of equal amplitude from two sources
are in phase, (align with overlapping crests), a
wave with twice the amplitude results
-this is called constructive interference
destructive interference- when waves are
completely out of phase and the waves cancel
diffraction- when a wave encounters an obstacle
or a slit that is comparable in size to its
wavelength, it bends around it
-diffraction of light through two slits separated by a
distance comparable to the wavelength of the
light results in an interference pattern
-dark lines are waves out of phase
-bright lines are waves in phase
Particle Nature of Light
photoelectric effect- metals emit electrons when
light shines on them
*especially the alkali metals
-used in solar calculators
-Einstein proposed that light energy must come
in packets
photon/quantum- particles/packets of light
-he also said that the amount of energy in a
photon depends on its frequency
E = hν
E = energy in joules
h = Planck’s constant = 6.626 x 10 -34J∙s
ν = frequency (1/s, s-1, Hz)
-since ν = c/λ, the energy of a photon can also be
expressed as:
E = hc
λ
-to find number of photons = Epulse / Ephoton
-electrons emit light when they are excited by the
passage of an electric discharge through an
element
atomic emission spectrum- range of
wavelengths emitted by a particular element
that can be used to identify an element
ex- neon lights- each noble gas will give a
specific color (He= pink, Ne= orange/red,
Xe= blue, Kr= whitish)
ex- fireworks- each element present will give a
particular color (Na= yellow, Sr= red, Ca=
orange)
page 292
-Neils Bohr said that e- travel around the nucleus
in circular orbits (energy levels)
*e- are at fixed distances from nucleus
*radiation was emitted or absorbed only when
an electron jumped from one level to another
Louis de Broglie
-stated that a single electron traveling through
space has a wave nature
-its wavelength is related to its kinetic energy
λ = h/mv
v = h/mλ
λ = wavelength
h = Planck’s constant (6.626x10-34 J·s)
m = mass of electron (9.11x10-31kg)
v = velocity (m/s)
**1J = 1kg·m2/s2
Example- Calculate the wavelength of an
electron traveling with a speed of 2.65x106m/s
λ = h/mv
(6.626x10-34 kgm2/s2·s)
(9.11x10-31kg)(2.65x106m/s)
=2.74 x 10-10m
For Practice 7.4 page 297
Heisenberg’s Uncertainty Principle
-states that it is impossible to know both the
velocity and position of a particle at the same
time
-Remember where electrons are found in an
atom!!
-surrounding the nucleus in electron clouds or
energy levels
Quantum Mechanics and the Atom
Principal Quantum Number (n)
-the energy level
-determines the overall size and energy of an
orbital (where electrons are held)
-n can be equal to 1, 2, 3, 4, 5, 6, 7
-distance electron is from the nucleus increases
as n increases
Angular Momentum Quantum Number (l)
-determines the shape of the orbital
-shapes are s, p, d, or f
-when given a value of n, l can be any integer
including zero up to n - 1
ex: n = 1
l=0
ex: n = 2
l = 0, 1
-to avoid confusion between n and l, values of l
are often assigned as letters
Value of l
Shape of orbital
l=0
s
l=1
p
l=2
d
l=3
f
Back to examples:
#1: n = 1 l = 0 is in first energy level with s
orbitals
#2: n = 2 l = 0, 1 is in the second energy level
with s and p orbitals
Atomic Orbital Shapes
s-orbital
-spherically shaped
-one shape, one orbital
-lowest energy orbital
p-orbital
-peanut/dumb bell shaped
-three shapes, three orbitals
d-orbital
-clover shaped
-five shapes, five orbitals
f-orbitals
-flower shaped
-7 shapes, 7 orbitals
energy level
n=1
n=2
n=3
n=4
# of sublevels Type of sublevel
1
1s
2
2s,2p
3
3s, 3p, 3d
4
4s, 4p, 4d, 4f
ex: how many orbitals in 3d?
5
how many orbitals in 4s?
1
how many orbitals in 2p?
3
how many orbitals in 2s?
1
how many orbitals in the third energy level?
9
1 from s, 3 from p, 5 from d
-Orbitals with the same value of n are said to be
in the same principal level
-Orbitals with the same value of n and l are said
to be in the same sublevel
Magnetic Quantum Number (ml)
-specifies the orientation of the orbital
-equal to integer values, including zero ranging
from +l to -l
ex: l = 0
ml = 0
ex: l = 1
ml = -1, 0, +1
ex: What are the quantum numbers and names of
the orbitals in the n = 4 principal level?
How many orbitals exist?
n=4
l
ml values
orbitals
0
0
4s
1
-1, 0, +1
4p
2
-2, -1, 0, +1, +2
4d
3
-3, -2, -1, 0, +1, +2, +3
4f
**16 total orbitals
Try For Practice 7.5 page 303
Example 7.6 page 303
For Practice 7.6 page 303