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108 Cards in this Set

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Atoms and molecules are governed by same or different laws?
Atoms and molecules are not governed by the same physical laws as larger objects
Max Planck discovered?
Energy is continous, and Atoms and molecules emit energy only in certain discrete quantities or quanta.
What is a wave?
vibrating disturbance by which energy is transmitted
How do water waves travel?
Wave repeats itself at regular intervals.
Waves can be characterized by?
length, height, and number of waves per second
What is wavelength?
distance between identical points on successive waves
What is frequency?
number of waves that pass through a particular point in 1 second
What is amplitude?
vertical distance from the midline of a wave to the peak or trough
What is speed?
Depends on the type of wave and nature of the medium. Speed is a product of wavelength and frequency
u = yV
What is wavelenght and frequency measured in?
m, cm, nm.
1 Hz = 1 cycle/second
Visbile light is made up of?
Electromagnetic waves
What are Electromagnetic waves?
Waves with an electrical field component and a magnetic field component
The two components of electromagnetic waves differ in?
Same speed, but travel in perpendicular planes
What is electromagnetic radiation?
Emission and transmission of energy in the form of electromagnetic waves
What speed do electromagnetic waves travel at?
3.00 * 10^8 m/s
Long waves
Are emitted from large antennas (radio, cell phones). Radio waves lowest frequency
Short waves
Have higher energy radiation. Gamma rays have the shortest wavelenght and highest frequency
What is quantum?
smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation
What is the wavelength (in m) of an electromagnetic wave whose frequency is 3.64 * 10^7 Hz?
ANSWER
What is the frequency (in Hz) of a wave whose speed is 713 m/s and wavelength is 1.14 m?
ANSWER
What is Planck's constant?
E=hv
H= 6.63 * 10^-34
What is the photoelectric effect?
Electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency called the
Threshold frequency
Number of electrons depends on?
intensity of light but energy of electrons does not
Einstein theorized light is made up of?
A stream of particles called photons.
What do you need to break electrons free from a metal?
Requires light of sufficiently high frequency
What is KE and BE?
E = hn = KE + BE
KE = kinetic energy of electron
BE = binding energy of the electron in the metal
The higher the frequency the greater the KE
KE is dependent on?
Frequency of the light. Ejected
Light behaves as?
Both as a particle and wave depending on the property being measured. All matter actually exhibits this dual nature.
The energy of a photon is 5.87 * 10-20 J. What is the wavelength in nm? h = 6.63 * 10-34 J*s

A photon has a wavelength of 624 nm. Calculate the energy of the photon in J.
ANSWER
What is an emission spectra?
Either continous or line spectra of radiation emitted by substances
What is a line spectra?
The light emmission only at specific wavelenghts. Produced by atoms
Continous
Emission spectra of the sun or heated solids
Why is Bohr's model no accurate?
Because it does not explain the spectral lines
What is Rydberg's constant?
Rydberg constant (RH) = 2.18 * 10^-18 J
Energy of electron
Where are free electrons?
infinitely far from the nucleus
Why is there a negative sign in equation of Rydberg's constant?
Negative sign – is to assign a lower energy of electron in an atom than the energy of the free electron (arbitrarily assigned a value of zero)
What happens as the electron gets closer to the nucleus?
Becomes more stable and E becomes more negative, which corresponds to the most stable state.
What is the ground state?
The lowest energy state of a system or most stable
What is the excited state?
Higher energy than the ground state
When is radiant energy emitted?
When electrons drop from a higher energy orbital to a lower energy orbital
The quantity of energy produced is dependent only on what?
Initial and final states
If an electron starts at ni and drops to a lower energy state of nf the change in energy is given by Equation=
What happen in the states when energy is given off.
Ni>Nf change in energy is negative
Each line on the emission spectrum corresponds to?
To a transition in the H atom
When a large number of H atoms are examined all the lines of the spectrum are visible
Electrons bound to a nucleus behave like?
Electrons bound to a nucleus behave like a standing wave
Waves that can be generated by plucking a string
Some points on a standing wave are
Nodes
Do not move at all
The amplitude at this point is zero
Nodes are located at the end of the string and maybe in the middle
De Broglie says that if an electron does not behave like a wave then?
De Broglie said that if an electron does behave like as wave then the wave must perfectly fit the circumference of the orbit
The circumference of the orbit is related to the wavelength by the equation
=
When can a particle be a wave and a wave be a particle?
A particle in motion can be treated as a wave
A wave can also exhibit properties of a particle
Protons can be accelerated to speeds near the speed of light in particle accelerators. Estimate the wavelength (in nm) of such a proton moving at 2.90 * 108 m/s. (mp = 1.673 * 10-27 kg)
A baseball has a mass of about 255 g. Calculate the wavelength of the baseball if it is thrown 100. mph.
Answer=
What is Heisenberg uncertainity principle?
It is impossible to know simultaneously both the momentum p and the position of a particle
Applying the Heisenberg uncertainty principle to the H atom?
We see that the electron can not orbit the nucleus in a circular orbital.
If this were the case then we could know both the position and momentum of the electron at the same time.
Erwin schrodinger formulated what?
Formulated an equation to describe the behavior and energies of submicroscopic objects
This equation is very complicated and requires Calculus to solve
The equation incorporated?
The Schrödinger equation incorporates particle behavior of electrons in the form of mass and wave behavior in the form of wave function (y)
Why is the wave funciton significant?
Is that the square of the wave function (y2) is proportional to the probability of where the electron is located
Where is an electron most likely to be?
The most likely place an electron will be is where y2 is greatest
What tells Schrodinger equation tell us?
The Schrödinger equation gives possible energy states and identifies the wave function of the electrons.
These are characterized by quantum numbers. Quantum mechanics gives probability of an electron in a particular region of the atom (electron density)
In quantum mechanics the orbits are called?
Atomic orbitals
What is an atomic orbital?
The wave function of an electron in an atom.
This is to differentiate from the orbits in Bohr’s model.
Each atomic orbital has a characteristic energy and therefore a characteristic distribution of electron density.
An assumptions must be made
The difference between hydrogen and atoms with more than one electron is not that large.
What are quantum numbers?
Describe the distribution of electrons in hydrogen and other atoms.
What are three quantum numbers that describe the distributioni of electrons?
Principal quantum number
Angular momentum quantum number
Magnetic quantum number
What is the fourth quantum number that describes the behavior of a specific electron?
Spin quantum number
Principal quantum numbers
Represented by n
Can have values of integers
Relates the average distance from the electron to the nucleus in a particular orbital.
Larger the n what happens?
The greater distance of an electron in the orbital from the nucleus and therefor the larger the orbital.
Angular Momentum Quantum Number
Represent by l
Tells the shape of the orbital
Dependent on n
For any n, l = any integer from 0 to (n-1)
For n = 1, l = 0
For n = 3, l = 0, 1, or 2
l is normally designated by the letter that symbolizes the different atomic orbitals
Magnetic quantum number
Represented by ml
Depends on l
For any value l, there are (2l +1) values for ml
If l = o then ml = 0
If l = 1 then there are three possible values of ml, (-1, 0, 1)
The value of ml indicates the number of orbitals in the subshell with value l
Spin quantum numbers
Represented by ms
It was noticed that the application of a magnetic field could split the lines in an emission spectra
The only way this could be explain is if electron behave as tiny magnets
If the electrons are thought of as spinning on their own then the magnetic field can be explained
The spinning charge generates a magnetic field
Spin quantum numbers are always?
–½ or +½
Atomic orbital related to angular momentum
-
What is a shell?
A collection of orbitals with the same value of n
What are subshells?
Orbitals with the same n and l value are called subshells
For example n = 2
Two subshells: l = 0 and l = 1
Called the 2s and 2p subshells
What is the shape of the orbitals?
Shapes are not well defined
Wave function defining orbital extends from the nucleus to infinity
It is convenient to think of the orbitals as having a shape
It is especially helpful when talking about chemical bonds
What shape and size are s orbitals?
All s orbitals are spherical
The s orbitals do change in size however
The increase in size is the reason for the increase in the principal quantum number
Electron density
Falls off rapidly as the electron get farther from the nucleus.
p orbitals start with the principal quantum number? What happen when n=2, and l=1?
2
three possible orbital so there are 3 2p orbitals
What are the shape, and size of orbitals?
They are oriented along the axes of a 3-d plot
The three orbitals differ only in the orientation
They are identical in shape, size and energy
p orbital are thought of as two lobes on either side of the nucleus
d orbitals
n must equal at least 3 and l must equal 2 for the d orbitals to exist
How many d orbitals are there?
There are 5 d orbitals
The orbitals differ in orientation as well as one having a different shape.
All 3d orbitals have the same energy
d orbitals which have a larger n value have similarly shaped orbitals that are larger
Why are f orbitals important?
are important for accounting for the behavior element with atomic number > 57
In this class we are not concerned with orbitals having l > 3
Give the quantum numbers associated with the following orbitals:
2p
3s
5d
-
Energy of orbitals increase as?
n increases
1s<2s=2p<3s=3p=3d<4s=4p=4d=4f<…
Does electron density change for 2s and 2p orbitals?
Although the electron density is different for 2s and 2p orbitals the energy remains the same
Which is orbital is the most stable?
1s
The total energy depends on what?
The total energy depends on the sum of orbital energies as well as the repulsive forces
It turns ends up that the total energy is lower when the 4s orbital fills before the 3d
Order of atomic orbitals filling
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p
2s quantum numbers
-
Ms
has no affect on energy, size, shape, or orientation of the orbital but determines how electrons are arranged in an orbital
What is electron configuration?
How the electrons of an atom are distributed among the orbitals
This is how the electrons are distributed in a ground state atom
The number of electrons in an atom is equal to?
Atomic number
Ground State H
-
Pauli exclusion principle?
No two electrons in the same atom can have the same four quantum numbers.
If they have the same n, l, and ml, then they must have different ms.
These two electrons would be in the same orbital but have opposite spins.
Thus each orbital can contain only two electrons
Paramagnetism
Contain net unpaired spins and are attracted by a magnet
Diamagnetism
Do not contain unpaired spins and are slightly repelled by a magnet. A He atom with opposite spins in the orbital
What happens if the spins in an orbital do match up?
The magnetic fields reinforce each other. This would make an atom paramagnetic.
Odd and even numbered atoms have?
Odd numbered atoms always have one or more unpaired electrons
Even numbered atoms may or may not have unpaired electrons
Which orbital is filled first?
The 1s orbital is filled before electrons are start to fill the 2s or 2p orbital
2s and 2p orbitals
Both the 2s and 2p orbitals have electrons that spend more time away from the nucleus than electrons in the 1s orbital
The electrons of the 2s and 2p orbitals are shielded from the attractive forces of the nucleus by the 1s electrons
This reduces the electrostatic interactions between the nucleus and the 2s and 2p electrons
Shielding
Experimentally the 2s orbital gives us a lower energy than the 2p
Although the 2s electron spend more time on average farther from the nucleus than a 2p electron; the denisty near the nucleus is greater for a 2s electron
So the 2s orbital is more penetrating
The 2s orbital is less shielded
For the same values of n, the penetrating power decreases as l increases
How is the stability of the electron is determined?
The stability of the electron is determined by the strength of attraction to the nucleus
Shielding effect
2s orbitals are less shielded than 2p orbitals so it follows that 2s orbitals have lower energy. Less energy is required to remove a 2p electron than a 2s electron
Hund's Rule
The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins
Rules for assigning electrons to orbitals
Each shell (or principal quantum number) n contains n subshells
Each subshell consists of quantum number l contain (2l + 1) orbitals
No more than 2 electrons can be placed in an orbital
The maximum number of electrons in principal level n is equal to 2n2
How many electrons can be present in the prinicpal level n=4?
What are the principal quantum numbers for the last electron in boron (B)?
-
Aufbau principle
As protons are added one by one to the nucleus to build up elements, electrons are similarly added to the atomic orbitals
Noble gas core
a method of showing electron configurations where the noble gas most nearly preceding the element being considered is used.The noble gas is followed by the electron configuration of the most highly filled subshells
Transition metals have either
Have either incompletely filled d orbitals or give rise to cations that have incompletely filled d subshells
Two irregularities in the fourth preiod
Chromium – [Ar]4s13d5
Copper – [Ar]4s13d10
The reason for this is that there is actually more stability in a half-filled or filled d orbital
Lanthanides and Actinide
Lanthanides – have incompletely filled 4f orbitals or readily give rise to cations with incompletely filled 4f subshells
Actinide series – last row of elements, most are not found in nature but have been synthesized
Write the ground-state electron configuration for Sr.
Write the ground-state electron configuration for Ga.
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