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What is the Bohr Model? What are its 3 components? What are their charges and atomic masses?
The Bohr model depicts a structure for an atom. It places positive Protons (+1, 1 amu or 1.67x10-27 kg) and neutral Neutrons (0, 1 amu or 1.67x10-27 kg) at the center of the atom (its nucleus), and negative Electrons(-1, 0.0005 amu or 9.12x10-31 kg) on the outer shells of the atom. These shells surrounding the nucleus make orbitals that have specific energies associated with each level.
What does an element symbol look like on a Periodic Table. What is Z? What is A? what do they signify?
Z is the atomic mass which signifies the number of protons inside an atom of an element. A is the mass number that signifies the number of protons and neutrons in an atom.
What is an isotope?
Atoms of the same element that have different numbers of neutrons but the same number of protons. Therefore the mass number would be different but the atomic mass would be the same.
What are cations and anions? Which are smaller and Why?
Cations are positively charged ions and anions are negatively charged ions. Cations are positive because they have fewer electrons than protons and Anions have fewer protons than electrons. Cations are smaller than their neutral counterpart and anions are larger, this is due to greater attraction forces with fewer electrons in cations and larger repulsion forces in anions.
What are some group trends found in the periodic table? some period trends?
Groups are vertical bunches on a periodic table, Periods are horizontal bunches on a periodic table. As you move down a group you increase in atomic radius. and decrease electronegativity. As you move from left to right across a period, you decrease atomic radius and increase electronegativity. Elements within the same group have similar chemical and physical properties
Where are the halogens? the Nobel gases? transition metals? Alkali and alkaline metals?
Where are the s, d, p, and f blocks? what does the letter signify?
The block letter signifies what orbital the valence electron is in.
What is the difference between a metal and a non-metal?
Metals are larger atoms that have loosely attached electrons. Electrons can be easily lost and form cations and are great conductors for heat and electricity. They can form ionic bonds with nonmetals. Nonmetals are smaller and hold tightly on to their electrons. they like to gain electrons and form anions. They have lower melting points and also make covalent bonds with other nonmetals.
Why are periodic trends largely dependent on atomic radius?
Smaller atoms have their nucleus closer to their valence electrons. Therefore the protons and electrons are held closer together making them electronegative, higher in ionization energy, greater in electron affinity, and less metallic in nature.
Why cant larger atoms form Pi bonds?
If the two atoms are large, these parallel orbitals cannot overlap well and pi bonds do not form.
What are the four quantum numbers? what are their symbols, what do they represent?
1st: Principle quantum number (n)- Gives shell
2nd: Angular momentum quantum number (l)- gives subshell/Orbital ( shape: 0=s, 1=p, 2=d, 3=f )
3rd: Magnetic Quantum number (ml)- Gives orbital orientation (-l to +l)
4th: Electron Spin Quantum number (ms)- gives the spin (-1/2 to +1/2)
What is the Pauli Exclusion Principle? and What is the Heisenberg Uncertainty Principle?
The Pauli Exclusion principle says no two electrons in the same atom can have the same set of four quantum numbers. The Heisenberg Uncertainty states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle
How do cations and anions effect electron configuration?
Cations move back an element for every electron missing. Ex: Cu2+ would turn into Co. Anions move forward for each additional electron. Ex: Cl- turns into Ar
How do electrons move up energy levels? What happens when an electron drops to a lower energy level?
electrons can only move up energy levels if there is enough energy to overcome the gap between the current energy level and the higher energy level. This is usually done by absorbing a photon with enough energy . When an electron drops an energy level a photon is released and it energy is exactly equal to the gab between the levels the electron dropped from and is now in.
What is the work function of a metal and how does it work?
The amount of energy required to eject an electron from the outermost shell of metal. It works by bombarding a metal with energy, if there is not enough then an electron will not be ejected, if there is too much then the excess energy will be transferred into kinetic energy for the ejected electron.
What are the different types of radioactive decay? What is captured/ ejected?
Alpha Decay: loss of one He nucleus
Beta Decay: Neutron is changed into a proton and electron is ejected
Electron Capture: Proton is changed into a neutron via electron capture
Positron Emission: Proton is changed into a neutron with the expulsion of a positron
Gamma Emission: Gamma rays emitted as a byproduct ( happens with all the other types of radioactive decay)
Note: Neutrons are protons+ electrons, and Protons are Neutrons+ a positron
What is a half-life?
the amount of time required for one half of the mass of a substance to disappear due to radioactive decay.
Do Anti-bonding or bonding orbitals have higher bonding orbitals? What are "in phases" and "out of phases" with bonding orbitals- which are attractive and which are repulsive?
Anti-orbitals (sigma star) have higher bonding energies compared to bonding orbitals. bonding orbitals stabilize the molecules because they are between the nuclei. Bonding orbitals contain electrons that are in phase are attractive, antibonding orbitals contains electrons that are out of phase and are repulsive.
ionic vs covalent bonds? Which types of elements form the highest ionic character?
ionic- formed when valence electrons are transferred from one atom to another, creating a cation (when atom loses an electron, positive charge) and anion (when atom gains an electron, negative charge)
covalent- formed when two atoms share valence electrons; when sharing is equal --> nonpolar covalent bonds occur
alkali or alkaline metals with halogens would create bonds with the highest ionic character
What makes good electrolytes?
Covalent compounds that dissociate 100% in water and make strong acids and strong base s make good electrolytes.
Ionic compounds that are soluble in water always make good electrolytes.
What is condosity?
The condosity of a solution is the concentration (molarity) of an NaCl solution that will conduct electricity exactly as well as the solution in question.
For example, for a 2M KCL solution, we would expect the condosity to be something more than 2.0. Why would we expect it to be above 2.0? Because potassium is more metallic than sodium. Thus, we know that it will be a better conductor. This means that NaCl solution will have to be slightly more concentrated to conduct as well as the KCl solution.
What are the bond length and Bond energy? How are bonds made and broken with respect to energy?
Bond length: the distance between the two nuclei forming a bond
Bong Energy: the amount of energy required to BREAK a bond.
Energy is always required to break a bond. Energy is always released when a bond is formed. That's why unstable compounds require lower amounts of energies to break a bond and more stable compounds require more energy to break a bond.
When a molecule is combusted with oxygen then what happens to the covalent bonds? Do more or less stable molecules have higher heats of combustion?
Heat of combustion is the amount of energy that gets released when a molecule is combusted with oxygen. ALL the covalent bonds will be broken and reformed in a radical reaction. The less stable a molecule is the higher heat of combustion it has
What are coordinate covalent bonds?
A coordinate covalent bond is a covalent bond in which one atom (i.e., the donor atom) supplies both electrons.
Donor molecules need lone pairs and the recipient molecule must have an empty orbital.
how do you derive the empirical formula from percent mass?
1. Change percent mass for grams for each element
2. Grams to moles
3. the element with the least amount of moles gets divided into the other molar amounts . The number it can be divided is the subscript .
4. make sure subscripts are the lowest common denominator
What are the steps for balancing a Reaction?
1) Balance the number of carbons
2) Balance the number of hydrogens
3) Balance the number of oxygens
4) Balance the number of any remaining elements
( use fractions if necessary and multiply sides by the denominator of any fractions)
How do atomic weight and molecular weight differ? What is molar mass? What is Avogadro's number?
Atomic weight is the weight of the individual atoms within a compound, When summed together they form the Molecular weight. The mass of a given chemical element or compound divided by moles is the Molar Mass. Avogadros number is 6.022x10^23
How do you determine the limiting reagent?
1. Start with converting a balanced equation into moles
2. compare the number of moles to the number of moles required to run rxn
3. The compound with the least amount of moles required is the limiting reagent.
What is the difference between theoretical, actual, and percent yield? Can catalysts increase yield? How else could yield be increased?
Theoretical yield is how much product would hypothetically be produced.
Actual Yield is the amount of product that does get produced
Percent yield is the amount of product that got produced compared to the amount of product that theoretically could have been produced.
Catalysts increase the rate of the reaction, but they won't increase the amount of product that is produced. One would need to add more of the limiting reagent (this increases yield but not % yield), or one would have to remove the product as it was produced to shift the equilibrium to the right.
What is the general rule of thumb to figure out how many moles of oxygen are needed to for combustion?
Add 1 for evet carbon and subtract 0.5 ( half) for each oxygen.
What is the equation for law of mass action?
NOTE: pure liquid and pure solids are not included
What is The Reaction Quotient (Q) relationship to K?
K is the equilibrium constant
Q is the same as K but for all other points that are not at equilibrium.
When K is larger than Q ( K>Q ) ---> reactions proceed to the right (to the product)
When K is smaller than Q ( K<Q ) <--- reaction will proceed to the left (to the reactants)
Note: Alphabetize K and Q and follow the direction of the greater or less than symbol
What is Le Chatelier's principle? How does adding/removing products/reactants affect equilibrium? what about pressure and temperature?
The idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change to re-establish equilibrium.
When more product is added then the reaction shifts towards the products. When products are removed then reaction moves towards the products. The same goes for Reactants.
Increasing pressure would cause equilibrium from the side of more gas molecules to the side of fewer gas molecules.
The equilibrium shift will change to counteract changes in temperature. If the temperature is increased then the reaction will move to lower the heat.
Kinetics is how quickly or slowly a species reacts.
Rate is the change in molarity in seconds.
How do collisions cause reactions? What is a endothermic/ exothermic reaction?
For a reaction to occur, reactants must collide with enough energy to overcome the energy of activation and must have the correct spatial orientation.
endothermic reactions (+delta H) absorb energy from the surrounding that is in the form of heat. Exothermic reaction (-delta H) releases energy into the surrounding of the system.
What is the rate law? What assumptions can be made regarding rate laws?
an expression for the rate of a reaction in terms of the concentration of reactants.
The assumptions are that reactions can only go forwards and only the first few seconds of a reaction are considered
How is order calculated and what are the different kinds?
Order can be calculated using experimental data.
1. A comparison of the trails needs to be done. The two trials chosen must have different reactant concentrations, but must be the same in all other parameters ( temp, pressure, concentrations, etc. )
2. Then compare the factor by which the rate and the reactant concentration changed .
3. solve fore Y- the order of the reaction using X^Y=Z
Y can either be 0,1, or 2.
What are the formulas for the rate order graphs?
ZERO- [A] : slope -k
FIRST- ln[A] : slope -k
SECOND- 1/[A] : slope +k
In Multi-Step reactions, a slow step is what?
The rate determining step ALWAYS. If it is the first step then a rate law can be written like it is the only step. If it is the second step, then the products of the fort step are written as the reactants of the second step.
What are catalysts? How do rate laws change when a catalyst is involved?
Chemical agents that selectively speed up chemical reactions without being consumed by the reaction.
Rate laws are supposed to include the rate laws for both catalyzed and uncatalyzed reactions because the catalyzed reaction will proceed at a much after rate, when writing the rate laws they can be written for the catalyzed reaction alone.
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