Chapter 7 Quantum Mechanical Model Of Atom Flashcards
Forms the foundation of chemistry
Quantum Mechanics
Electron behavior determines much of the
Behavior of Atoms
Why is directly observing electrons in the atoms impossible?
The electron is so small that observing it changes its behavior
The ___ explains the manner in which electrons exist and behave in atoms
Quantum - Mechanical Model
What does the Quantum - Mechanical Model explain?
- Why some elements are metals and some are Nonmetals
- Why some elements gain one electron when forming an anion, while others gain two
- Why some elements are very reactive while others are practically inert
- Periodic patterns we see in the properties of elements
Light is a form of
Electromagnetic Radiation
Why is light composed of ?
Perpendicular oscillating waves, one for the electric field and one for the magnetic field
An ___ field is a region where an electrically charged particle experiences a force
Electric
A ___ field is a region where a magnetized particle experiences a force
Magnetic
What is the speed of light?
3.00 x 10^8 m/s in a vacuum
Wha is the speed of sound?
340 m/s
- The ___ is the height of the wave
* The distance from node to crest
Amplitude
The larger the amplitude, the ___ the light
Brighter
- The ___ is a measure of the distance covered by the wave
* The distance from one crest to the next
Wavelength (l)
- The ___ is the number of waves that pass a point in a given period of time
- The number of waves = of cycles
Frequency (n)
What are the units for frequency ?
Hertz (Hz) or cycles = s-1
1 Hz = 1 s-1
The ___ is proportional to the amplitude of the waves and the frequency
Total Energy
The larger the amplitude, the ___ force it has
More
The more frequency the waves strikes, the ___ total force there is
More
For waves traveling at the same speed, the shorter the wave length, the ___ frequently they pass
More
Wavelength and frequency of electromagnetic waves are
Inversely proportional
Because the speed of light is constant, if we know the wavelength we can find
The Frequency and vice versa
What is the formula for frequency ?
v(s-1) = c(m/s) / ?(m)
The color is determined by
It’s wavelength (or frequency)
White light is a mixture of
All colors of visible light (a spectrum)
When an object absorbs some of the wavelengths of white light and reflects others
It appears colored
The observed color is predominately
The colors reflected
Different wavelength, different
Color
Different amplitude, different
Brightness
Visible light compromises only a small fraction of all wavelengths of light - called
The Electromagnetic Spectrum
Shorter wavelength (higher frequency) light has ___ energy
Higher
Radio wave light has the ___ energy
Lowest
Gamma ray light has the ___
Energy
High-Energy electromagnetic radiation can potentially damage biological molecules
Ionizing radiation
What is the order of electromagnetic waves from low frequency and energy to high frequency and energy ?
- Radiowaves
- Microwaves
- Infrared
- Visible
- Ultraviolet (UV)
- Xray
High-Energy radiation can also be used to kill
Cancer Cells
The interaction between waves is called
Interference
When waves interact so that they add to make a larger wave it is called
Constructive Interference
• Waves are in-phase
When waves interact so they cancel each other it is called
Destructive Interference
• Waves are out-of-phase
When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it
Diffraction
• traveling particles do not diffract
The diffraction of light through 2 slits separated by a distance comparable to the wavelength results in an ___ ___ of the diffracted waves
Interference Pattern
An interference pattern is a characteristic of
All light waves
Destructive interference
Path lengths differ by ?/2
Constructive Interference
Equal path lengths
Waves out-of-phases make ___ spots
Dark
Waves in-phase make ___ spots
Bright
It was observed that many metals emit electrons when light shines on their surface
Photoelectric Effect
Classic wave theory attributed this effect to the ___ ___ being transferred to the ___
Light Energy, Electron
According to the Classic Wave Theory, if the wavelength of light is made ___, or the light waves intensity was made ___, more electrons should be ejected
Shorter, Brighter
If a dim light were used they would be a ___ before the electrons were emitted
Lag in time
In experiments it was observed that there was a minimum frequency needed before electrons would be emitted (regardless of intensity)
Threshold Frequency
High-Frequency light from a dim source caused electron emission
Without any lag time
Einstein propose that the light energy was delivers to atoms in packets, called ___ or ___
Quanta, Photons
The energy of a photon of light is ___ to its frequency
Directly proportional
The proportional constant between a photon of light and its frequency is called
Planck’s Constant (h)
What is the value of Planck’s Constant ?
6.626 x 10^-34 J•s
What is the equation for total energy?
E = hv = (h•c) / ?
Order wavelength (short to long)
- Gamma
- UV
- Green
- Red
- Microwaves
Order by energy (least to most)
- Microwaves
- Red
- Green
- UV
- Gamma
Order by frequency (low to high)
- Microwaves
- Red
- Green
- UV
- Gamma
One photon at the threshold frequency gives the electron just enough energy for it to escape the atom
Binding Energy (f)
When irradiated with a ___ wavelength photon, the electron absorbs more energy than is necessary to escape
Shorter
The excess energy becomes ___ energy of the ejected electron
Kinetic
Equation for Kinetic Energy
Kinetic Energy = E photon - E binding
KE = hn - f
When atoms or molecules absorb energy, that energy is often released as
Light Energy
Ex: fireworks, neon lights
When emitted light is passed through a prism, a pattern of particular wavelengths of light is seen that is unique to that type of atom or molecule
Emission Spectrum
• Non-continuous
• Can be used to identify the material
Prism separates component
Wavelengths
Rydberg analyzed the spectrum of hydrogen and found that it could be described with an equation that involved an inverse square of integers
1/? = 1.097 x 10^7 m^-1 (1/n1^2 - 1/n2^2)
The atom contains a tiny dense center called the
Nucleus
• 1/10 trillionth the volume of the atom
The nucleus is essentially the ___ of the atom
Entire mass
The nucleus is ___ charged
Positively
Electorons are ___ and ___ particles
Moving and Charged
According to classical physics, moving charges give off ___
Energy
Based on classical physics, electrons should constantly be
Giving off energy, make the atom flow, and lose energy when it crashes into the nucleus and cause the atom to collapse
• but it doesn’t (problem with Rutherfords Nuclear Model of the Atom)
Bohr developed a model of the atom to explain how
The structure of the atom changes when it undergoes energy transitions
Bohr’s major idea was that the energy of the atom was ___, and that the amount of energy in the atom was related to the electron’s position in the atom
Quantized
Quantized means that
The atom could only have very specific amounts of energy
The electrons travel in orbits that are at a fixed distance from the nucleus
Stationary states
The energy of the electron was ____ the distance the orbit was from the nucleus
Proportional
Electrons emit radiation when they “jump” from an orbit with ___ energy to an orbit with ___ energy
Higher, lower
The distance between the orbits determined the energy of the ___ produced
Photon of light
De Broglie predicted that the wavelength of a particle was ___ to its momentum
Inversely Proportional
Formula for the wave character of electrons
?(m) = h(kg•m^2/s^2 •s) / mass(kg) • velocity(m•s^-1)
What was proof that electrons had wave nature
The demonstration that a beam of electrons would produce an interference pattern as waves do
Wave nature =
Interference Pattern
Particle nature =
Position, which slit it is passing through
When you try to observe the wave nature of the electron, you ___ observe its particle nature (and vice versa)
Cannot
The wave and particle nature of the electron are
Complementary properties
• The more you about one the less you know about the other
Heisenberg stated that the product of the uncertainties in both the position and speed of a particle was ___ to its mass
Inversely Proportional
• the more accurately you know the positions of a small particle, the less you know about its speed
Definite, predictable future
Determinacy
Indefinite future, can only predict probability
Indeterminacy
According to classical physics, particles move in a path ___ by the particles velocity
Determined
Because we cannot know both the position and velocity of an electron, we cannot predict the path it will follow
Indeterminacy
For an electron with a given energy, the best we can do is
Describe a region in the atom of high probability of finding it
Allows us to calculate late the probability of finding an electron with a particular amount of energy at a particular location in the atom
Schrödinger’s Equation
A plot of distance vs. Y2 represents an ___, a probability distribution map of a region where the electron is likely to be found
Orbital
Calculations show that the size, shape, and orientation in space of an orbital are determined to be three integer terms in the wave function called
Quantum Numbers
- Characterizes the energy of the electron in a particular orbital
- n (can be any untether => 1)
- The larger the n value, the more energy and the larger the orbital
Principal Quantum Number, n
Principal Quantum Number Equation, n
E n = -2.18 x 10^-18 J (1 / n^2)
• Determines the shape of the orbital
• I can have an integer values from 0 to (n-1)
• Each value of ___ is called by a particular letter that designated the shape of the orbital
- s orbitals are spherical
- p orbitals are like two Ballons tied at the knot
- d orbitals are like four Ballons tied at the knot
- f orbitals are mainly like eight balloons tied at the knot
Angular Momentum Quantum Number, l
Each value of l is called by a particular letter that designates the shape of the orbital • s = • p = • d = • f =
- s = orbitals are spherical
- p = orbitals are like two Ballons tied at the knots
- d = orbitals are mainly like four Ballons tied at the knot
- f = orbitals are mainly like eight Ballons tied at knot
The ___ number is an integer that specifies the orientation of the orbital
• The direction in space the orbital is aligned relative to the other orbitals
Magnetic Quantum
Each set of n, l, and ml describes
One Orbital
Orbitals with the same value of n are in the same
Principal Energy Level
• Aka Principal Shell
Orbitals with the same values of n and l are said to be in the same
Sublevel
• Aka Subshell
When an electron is ___, it transitions from an orbital in a lower energy level to an orbital in a higher energy level
Excited
When an electron ___, it transitions from an orbital in a higher energy level to an orbital in a lower energy level
Relaxes
When an electron ___, a photon of light is released whose energy equals the energy difference between the orbitals
Relaxes
To transitions to a higher energy state,
The electron must gain the correct amount of energy corresponding to the difference in energy between the final and initial states
Electrons in high energy states are unstable and tend to
Lose energy and transition to lower energy states
Each line in the emission spectrum corresponds to the difference in
Energy between two energy states
The wavelength of lines in the emission spectrum of hydrogen can be predicted by
Calculating the difference in energy between two states
Both the ___ and the ___ models can predict these lines very accurately for a 1-electron system
Bohr and Quantum Mechanical
The energy of a photon released is equal to the difference in
Energy between the two levels the electron is jumping between
It can be calculated by
Subtracting the energy of the initial state from the energy of the final state
The probability of finding an electron at a particular point in space
Y2 is the probability density
• decreases as you move away from the nucleus
The ___ function represents the total probability at a certain distance from the nucleus
Radial Distribution
• Maximum at most probable radius
___ in the functions are where the probability drops to 0
Nodes
The ___ function represents the total probability of finding an electron at a particularly point in space
Probability Density
The ___ function represents the total probability of finding an electron within a thin spherical shell at a distance r from the nucleus
Radial Distribution
The probability at a point ___ with increasing distance from nucleus, but the volume of the spherical shell ___
Decreases, increases
The quantum l primarily determines
The shape of orbital
Orbitals are determined from
Mathematical wave functions
A wave function can have a __ or __ value
Positive and negative (as well as nodes where the wave function = 0)
The sign of the wave function is called its
Phase
When orbitals interact, their wave functions may be ___ (same sign) or ___ (opposite sign)
In-phase, out-of-phase
