Chemistry 20 AP unit

1. The central atom has fewer than 8 electrons due to a shortage of electrons (this applies to elements in group 2 and 13. Ex. hydrogen and boring boron)

2. The central atom has an odd number of electrons (less than 8) These molecules with a off number of electrons are sometimes referred to as free radicals.  (groups 13,15, and 17)

3. The central atom has more than 8 electrons. This only includes 3d orbital elements. Atoms in and beyond the 3rd period can have more than eight valence electrons.

1.For neutral molecules, a lewis structure in which there are no formal charges is preferrable to one in which formal charges are present.

2. Lewis structures with large formal charges are less plausible (likely to form) than those with small formal charges. 

3. Among lewis structures having similar distributions of formal charges, the most plausible (most likely to exist) structure is the one in which negative formal charges are placed on the more electronegative atoms.

Chadwick

Goldstein

A resonance structure is one of two or more lewis structures for a single molecule that cannot be represented by only one lewis structure. Resonance structures are a human made possibility that accounts for difference in the position of electrons for polyatomic species. 


(basically they are just different versions of how a molecule can be physcially built and different versions of how their electrons are arranged)

Formal charge= (number of valence electrons on atom) - (number of bonds) - (number of electrons on the valence shell after bonding)

You must determine the formal charge of the compound/ molecule (the formal charge of each individual atom, that is.)

Formal charge is the difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a lewis structure.

L=0---> s-oribtal

L=1---> p-orbital

L=2 ---> d-orbital

L=3 --->f-orbital

The magnetic quantum number provides the orientation of the oribtal around the center of the nucleus, where the magnetic quantum number is a range from -L to +L including 0. Magnetic quantum numbers can be thought of as orbitals containing the same energy amount where each orbital can contain up to two electrons. 


Ex.

We can reference the quantum numbers of our atom and use the formula:

L=n-1

The angular momentum describes the shape of an orbital, where each orbital can contain up to 2 electrons. In angular momentum, L can range from being equal to 0 all the way to 3 (atleast in AP chem) which corresponds to the orbital shape.

A principal quantum number (n=1 ---> n=7) describes the energy level in which an electron can be found (they are regions of specific distance from the nucleus of the atom). The larger the n value, the further away the electron is from the nucleus and the higher energy it has.

1st energy level= s-orbital (0)

2nd energy level= p-oribtals (-1, 0, +1)

3rd energy level= d-oribitals (-2, -1, 0, +1, +2)

4th energy level= f-orbitals (-3,-2,-1,0,+1,+2,+3)

The quantum mechanical orbitals have orientations in certain directions and they have shapes.

Shrodingers equations were able to predict the presence of certain regions in an atom where electrons are likely to be found. These locations are referred to as orbitals at various distances from the nucleus.

We cannot determine where the electron WILL be but we can predict its current location.

We are talking about the probablistic movement of an electron surrounding the nucleus of an atom as a wave.

 This equation calculates the change in energies in one step.

Lamda= h/(m times v (vector arrow))


where:

Lamda= wavelength (nm) convert to metres for this equation to match with velocity

h= plancks constant (6.63x10^-34 j.s)

m= mass (kg)

v with vector arrow= velocity (m/s)

The light wave/particle duality is the idea that light shows properites of waves but also shows properties of particulate matter (photons)

Planck's constant relates to frequency because the number he calculated corresponds to the amount of energy released per oscillation of the wave released from the electrons falling in their energy levels.

Plancks work showed that energy emitted from atoms occured in discrete amounts called quanta (singular=quantum) and not in waves as previously thought. Atoms would absorb and lose energy in these quanta amounts.

It also showed that when energy is added to an atom, electrons gain more energy and go up in energy levels. However, when those electrons release and lose their energy, the energy is lost as a photon (particles of EMR proposed by einstein) and they go down an energy level. They keep losing energy and releasing it as photons untill they go back to to their original energy level.

When the energy is emitted in these chunks (packets) called quanta they correspond to Planck's constant (6.63x10^-34 j.s) and their relationship to frequency.

c= (lamda) (v)

where c= speed of light (2.9979x10^8m/s)

lamda= wavelength (1nm=10^-9 m)

v= frequency (hz or 1/s or s^-1)

Out of frequency and energy, wavelength has an inverse relationship with both, proportional with none.

Frequency is the number of wavelengths (cycles) per second as it passes a certain point. Frequencies units are 1/s, s^-1, or Hertz

The crest is the top of the wavelength and the trough is the bottom.

Angstroms=10^-10m or nanometers= 10^-9m

1. Light can be described by its wavelength and frequency

2. Electromagnetic radiation with long wavelengths and low frequency have low energy

3. Electromagnetic radiation with short wavelength and high frequency have high energy

1. they all have wave-like behaviour

2. when in vacuum (place with no matter) they all travel at the speed of light (2.9979x10^8 m/s)

highest: Gamma rays

Lowest: X-rays

Rutherford's gold leaf expierment is an experiment that devised a nuclear model of the atom. In this experiment, Rutherford bombarded a gold leaf with with alpha particles (positivley charged helium particles). Due to the reflection and deflection of the alpha particles because of the repulsion of positive charges, Rutherford was able to find that the atom has a dense positive centre which he called a nucleus.

(-1.602 x 10^-19) Coulomb's (C)

Millikan's oil drop expirement was an expierment that determined the magnitude of the electron charge and the mass of the electron (9.11x10^-31 kg). How this expierment functioned was he put oil into a bottle and when the oil was released, it would go through an atomizer that would make the oil turn into droplets and spray these droplets into a chamber. As the oil droplets fell through the chamber, they would lose some electrons due to an x-ray, making them positivley charged. Now, there was a tiny gap in a metal plate inside of the chamber the oil droplets could go through. As the oil droplets fell through, they reached a new section of the chamber that had a plate above (the same one it passed through) and a plate below. On the plate below, a positive charge was turned on and on the plate above, a negative charge was turned on. These electric forces would end up balancing out with the gravitation force pulling down on the droplet and the oil droplet just floated in the middle of the chamber. Due to this, they were able to make observations (using a microscope that was attached to the chamber) and calculations that would allow them to determine the charge of each oil particle and then the charge of an electron.

ex.

Thomson's atomic model, also known as the plum pudding model, determined the presence of electrons and the fact that atoms contained negative charges. 

(its like a soup of positive charge with negativley charged electrons scattered throughout)

The periodic law states that the chemical and physcal properties of the elements vary in a period with their atomic number.

Atomic number.

An example of an early periodic table is Russian Dmitri Mendeleev's periodic table which arranged elements according to atomic mass. He put the elements with similar properties into groups. 

ex. 

• 1. matter is made of particles called atoms
• 2. atoms are unchangeable
• 3. atoms of an element are identical 
• 4. chemical reactions are rearrangements of atoms

That matter cannot be created nor destroyed.

Bohr developed the quantum model for the hydrogen atom, where the electrons in the hydrogen atom move around the nucleus in certain circular orbits. According to the emission line spectra for hydrogen, only certain energies were allowed by Bohr did not know why. Through his experiments, he noticed that when energy was placed into an atom, electrons could be moved into different energy levels. When energy is put into atoms and the electrons moved away from the nucleus into a higher energy level, it is said that they went from a ground state to an excited state. When the electrons returned from their excited state to the ground state, the atom gives off light at a certain energy level. This shows why the emission line spectra is different for each element.

As electrons move from the nucleus into different energy levels due to them gaining energy (higher and higher excited states), they give off that energy as they come back down to the nucleus, giving off different colors of light will be emitted from different atoms which will give us different emission line spectra.

Each of these spectral lines corresponds to a different electron transition from a higher energy state to a lower energy state (higher energy level to lower energy level). Every element has a unique atomic emission spectrum.

When white light passes through a prism, it will give a continuous spectrum of light (contains all wavelengths of visible light). However, when a gaseous element is heated or excited by electricity, it will emit discrete wavelengths of light as it gived off energy. When this light is viewed through a prism, it will show line specta (emission lines) unique to that element.

Where delta E= energy (in Joules)

n= quanta (amount of packets, 1,2,3...) we assume 1 packet of energy for now

h= Plancks constant (6.63x10^-34)

v= frequency (Hz, or 1/s, or s^-1)

Where:

E= energy (joules) --> energy stored /released when electrons "fall/rise"

Z= Z-effective (charge of nucleus) 

n= energy level of the electron (where the electrons have been moved to)

Energy is carried away by the emission of a photon

A positive sign for the change in energy indicates that the system has gained (absorbed) energy and is now less stable.

A negative sign for the change in energy indicates that the system has lost energy and is now more stable .

When they are closer to the nucleus.

Hund's rule states that when electrons are filling orbitals, of equal energy, they must fill the oribtals one electron at a time untill al orbitals in that energy level are full.

the Pauli exclusion principle states that no two electrons can have the same 4 quantum numbers, where each electron in the same orbital have opposite spins.

Heisenburg's uncertainty principle states that it is impossible to know both the momentum (movement) and the position of that electron at the same time. This is because when looking at movement, you have to look at the electron as a wave. But, when looking at the position of the electron, you have to look at it as a particle.

Lone pairs of electrons occur because of an "apparent spin" on a electron. This spin up and spin down occurs because electrons create a momentary magnetic dipole.

Outside ----> inside and not in reverse order of energy. 

Ex. 4s is removed before 3d.

removing electrons.

When the graph would become too long to view if the 1s subshell was included.

yes, because although it takes more energy to release electrons closer to the nucleus, there is more electrons to actually spend energy on and remove in the outer shells.

Because some electrons are closer to the nucleus than others meaning that the nucleus has a higher attraction to them than electrons in the outer energy levels meaning that the ones in the outer shells will be easier to remove than those in the inner shells.

A photoelectron spectrum graph is an electron count vs the binding energy of your atom or molecule. Each peak represents electrons in different subshells of an atom, where the peaks with the lowest binding energy correspond to the valence electrons. Meanwhile, the peaks with the highest binding energy correspond to the inner shell or core electrons.

High energy radiation such as x-rays or UV, to help determine the electronic structure of atoms and molecules. As the atom increases in energy, electrons become excited and are eventually ejected from the atom, where the number of electrons and their kinetic energy can be detected. Electrons=protons so they eject all the electrons present, counting untill there are none left. Using this info about the quantity of electrons allows the scientists to identify the atomic number which helps them identify what atom it is.

m/z or mass number

An isotope is an element that contains the same number of protons but different numbers of neutrons, changing the atomic mass.

A mass spectrometer seperates molecules in a sample based on their charge and mass, and just like in PES spectra, the intesity of the peak indicates the relative number of particles present. When a mass spectrum is created it can help scientists determine the different isotopes of an element and their relative abundance in a sample.

Linus Pauling suggested that that valence orbitals of atoms can combine and form hybrids of orbitals.

Double bonds contain one sigma bond and one pi bond. Triple bonds contain one sigma bond and two pi bonds

Sigma bonds from single bonds that are much stronger.

Pi bonds are when multiple bonds are formed through the overlapping of electrons in a side by side fashion, as the bonding electrons are found below the plane of the nucleus in p orbtials. When bonds are created, a single pi bond can only be created between two p-p oribtals, where a maximum of two pi bonds can be formed in any given compound. Because the electrons are further away from eachother, the bond length of a Pi bond is greater than a sigma bond thus resulting in a weaker overall bond.

Sigma bonds, almost always a single bond, are formed when orbitals (either s,p, or hybrid) overlap in end to end fashion, where the electrons are in between the nucleus of each bonding atom. Resulting in shorter bond lengths (the nuclei are attracted to the negative charge of the electrons) and stronger bonds.

Yes

true

Hybridization of orbitals is advantageous when it comes to bonding because hybridized orbitals are more focused in specific directions, allowing for better overlap when forming bonds. This leads to stronger bonds being created. As a result, compounds formed through hybridization tend to be more stable.

The electron configuration diagram for this carbon is wrong because there are 2 bonding electrons when carbon can in reality make 4 bonds. This problem can be fixed by moving the electron in the 2s orbital into the 2p (it will become a ps orbital after hybridization) orbital by hybridization of orbitals.

Ex.

To explain the molecular structure when the valence bond theory failed to explain bond formation when the central atom breaks the octet rule by having more than 4 bonds for a central atom.

Increase

The atomic radius decreases (because of increasing Zeff's and electronegativities) and the ionization energy of the atoms increases across periods and up groups due to the decreasing atomic radii described above. These varying ionization energies can affect a photo electron spectrum.

True

Electronegativity and the effective nuclear charge. This is because the higher the Zeff and the electronegativity, the more strongly the electrons are attracted to the nucleus and the smaller the atomic radius will become. However, if the Zeff and the electronegativity is big, the opposite will occur.

The atomic radii is used to determine the total distance from an atom's nucleus to the outermost orbitals of electrons and can be thought of as the observable trend in the size of an atom's circle as it gains more electrons.

In this shielding effect, the electrons closer to the nucleus shield eachother from the electrostatic attraction of the positive protons of the nucleus.

Ex. 

Effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom.

up and to the right.

Representing shared pairs of electrons with lines or dashes and showing the lone pairs as dots on individual atoms. 

Ex.