Chem 141 final Exam
The wavelength of the electron is 1.45x10⁻⁹m which is closest in size to a..
diameter of a carbon nanotube
molecules that are compounds
more than one molecule
translation
moving in one direction
gravitational force
only attractive force
You (a human being) are what kind of system?
open
Photoelectric effect
shows that there is a threshold frequency below which no electrons are ejected regardless of how much we increase the intensity -light photons are shined on a piece of metal and electrons are emitted
law
describes the phenomenon tells you WHAT
atoms that are elements
true, an element is made up of the same atom
3 centers of electrons
-120° -sp² -0 lone pairs=trigonal planar geometry and shape -1 lone pair= trigonal planar geometry and bent shape
bonding in diamond
-4 carbon bonds -sp³, geometry=tetrahedral, 109°
polar bonds
-when two atoms of different electronegativities bond, the electrons are not shared equally, results in a dipole
moles to grams
# of moles X (molar mass in g/1 mol)= grams
For the process shown in the diagram the ∆H is:
+ because heat is added to the reaction
For the process shown in the diagram the ∆S(entropy/arrangements) is
+ because in the gas phase the most arrangements can be created
2 centers of electrons
-0 lone pairs -sp -linear geometry -linear shape -180°
Why are metals shiny?
-Because they absorb photons and re-emit them -metals have molecular orbitals that are very close together in energy. They can absorb almost any wavelength of light because the gap b/w the leaves is negligible(unimportant). The absorbed light can then be re-emitted.
bonding in graphite
-C-C-C -sp², geometry=trigonal planar, 120°
hydrongen bonding interactions
-Intermolecular forces, not bonds 1. First must contain H covalently bonded to O, N, or F 2. must have O, N, or F atom with lone pair -interactions are very strong -also have dipole-dipole and LDFs
Why do metals tend to form cations while nonmetals form anions?
-It is easiest to achieve noble gas configuration by removing valence electrons from metals (which have few valence electrons) and adding them to nonmetals (which have many valence electrons) -Electrons are more attracted to the nuclei of non metals because they have higher effective nuclear charges
endothermic
-if the change in H is positive -heat goes into the reaction and the surroundings get colder Ex: sweat evaporating
the ionization energy of carbon (C) is:
-Smaller than that of fluorine (F) -The effective nuclear charge of carbon is smaller, so the valence electrons feel weaker pull from the nucleus -In carbon, the electron being removed is farther from the nucleus
What is the reasoning to support the claim that graphite will conduct electricity but diamonds will not conduct electricity?
-Some of the valence electrons are delocalized (free to move) in the pi bond that extends across the entire graphite structure -valence electrons are localized and cannot freely move in the covalent bonds in diamond
electronegativity
-ability to attract electrons to itself in a bond -depends on effective nuclear charge and size of orbitals -same trend as effective nuclear charge -increases across a row -decreases down a group
solid-energy of motion
-absent translation -very limited rotation -free vibration
Molecular orbital theory
-atomic orbitals combine to form an equal number of molecular orbitals -each orbital can contain up to two electrons -electrons in bonding orbitals stabilize the system -electrons in antibonding orbital make it less stable - electrons are delocalized
valence bond theory
-atomic orbitals overlap to form a bond -the greater the overlap, the stronger the bond -each bond made up of two electrons -electrons are localized in the bond
As two isolated He atoms move from far apart to the distance where they are most stable, the potential energy of the system will...
-increase because the electrons from one atom will repel the electrons from the other atom -PE ↑=repulsion -PE↓=attraction
simple ionic compounds
-contain a metal and non metal -metal has a low electronegativity and non metal has high electronegativity -metals form cations and nonmetals form anions -ionic compounds are neutral
Absorption spectra
-continuous spectra where electrons/energy are absorbed -light is missing -electrons occupy the ground state
What is the most stable interaction between two Xe atoms and when the interaction is broken, energy is?
-covalent bond -absorbed
path functions
-depend on how the change takes place -lower case letters Ex:heat and work
state function
-depending only on the initial and final states, does not depend on path taken Ex:the elevation of the campsite is a state function and it is independent of the paths taken to reach it and density, internal energy, enthalpy, entropy -upper case letters
thermal energy
-depends on how much material you have -movement associated with motion of particles (unit is joules)
temperature
-depends on the average KS of the particles -measure of "hotness" -direction of thermal energy goes from hot to cold -doesn't change until after the phase change is complete
Diamond
-does not conduct electricity (Electrons are localized b/w the two nuclei that participate in the bond. The electrons cannot more out of the area and are not mobile. To conduct electricity, charged particles must be able to move freely in molecular orbitals) -has a very high melting point (To melt diamond and allow the particles to move relative to one another C-C covalent bonds must be broken. Substances that exist as molecules tend to have lower melting points b/c the IMFs are overcome rather than covalent bonds)
Determining if polar bond
-draw lewis structure -draw arrows toward the most electronegative atom -if the arrows are facing each other, then the bond is polar -if the arrows are facing away from each other then they cancel out and there is no dipole
What is the shape of the hydronium ion, H₃O⁺?
-draw lewis structure -trigonal pyramidal b/c it loses one electron so there is only one lone pair
What is the electron center geometry and hybridization on the S atom in SF₂
-draw lewis structure -tetrahedral and sp³
What intermolecular forces would exist between molecules of CH₂Cl₂?
-draw lewis structures -london dispersion forces -dipole dipole interactions
Is BF₃ a polar molecule?
-draw the lewis structure -No, because the bonds between B and F are polar and the molecular shape of BF₃ is trigonal planar, therefore the electronegativity will pull in opposite directions and the bond dipoles will cancel out
What is the electron center geometry and shape of the molecule H₂S?
-draw the lewis structure -tetrahedral and bent
emission spectra
-electrons are excited up to higher energy -then drop and create a photon -photons create colored lines, the lines correspond to the frequencies of photons of light emitted
First law of thermodynamics
-energy cannot be created or destroyed (but it can be transferred or transformed)
When a covalent bond is formed between two hydrogen atoms...
-energy is released -a molecule is formed
Second law of thermodynamics
-for any change the total entropy of the universe must increase -the state of entropy of the entire universe, as an isolated system, will always increase overtime and changes in entropy of the universe can never be negative
What is the formal charge on each atom in the amide ion, NH₂-?
-formal charge=# of valence electrons in the neutral atom-# of bonds-# of free electrons - N=5-2-4=-1 - H= 1-1-0=0
Gas-energy of motion
-free translation -free rotation -free vibration
Diamond properties
-hard(3D network of strong bonds, you would have to break bonds to disrupt a crystal) -high mp/bp (same as hard) -does not conduct electricity(electrons are located in bonds between atoms-not free to roam. There is a large "band gap" between the bonding and antibonding orbitals) -translucent(light passes through or is reflected. To absorb light an electron must be promoted to a higher energy level.)
Graphite properties
-high mp -soft -slippery(sheets can slide over each other/only held together by LDFs) -grey/shiny(because it can absorb and emit photons of many wavelengths (just like metals) -conducts electricity(because electrons can move freely over the entire sheet within its delocalized pi MOs)
exothermic
-if the change in H is negative -heat goes out of the reaction and the surroundings get hotter Ex:wood burning, water freezing, chemical hand warmer
Entropy
-measure of the number of possible arrangements for a given state -more arrangements=higher probabilty
anions
-negatively charged -larger than corresponding atom -form when nonmetals gain electrons -charge usually corresponds to gain of electrons needed to fill the next full shell (noble gases)
trend of effective nuclear charge
-opposite of atomic radius -increases across a row -decreases down a group
cations
-positively charged -smaller than corresponding atom -form when metals lose electrons -form because energy is released when ion-ion interactions are formed
dipole-dipole
-present in polar substances -typically stronger than LDF for molecules of the same size -
liquid-energy of motion
-restricted translation -less free than gas rotation -free vibration
4 centers of electrons
-sp3 -0 lone pair= tetrahedral geometry and shape, 109° -1 lone pair=tetrahedral geometry and trigonal pyramidal shape, <109° -2 lone pairs= tetrahedral geometry and bent shape, <109°
London dispersion forces
-temporary dipoles -depends on size, surface area, and shape of molecule -present in all substances solid and liquid states -if nonpolar this is the only intermolecular force present
If the molar mass of the gas increases, what happens to the average velocity?
-the average velocity decreases -larger gases have smaller velocity
When gas molecules collide why don't they stick together?
-the molecules don't stick together because have enough energy to overcome the attractive interactions
sigma bonds
-they form end to end overlap of atomic/hybrid orbitals -free rotation is allowed around the bond -single bonds=sigma bond -double bonds=one sigma and one pi -triple bond=one sigma and two pi
Pi bonds
-they form side to side overlap of atomic orbitals -free rotation is not allowed around the bond -double bonds=one sigma and one pi -triple bond=one sigma and two pi
CH₄(g)+2O₂(g)→2H₂O(l)+CO₂(g) How many molecules of CH₄ will remain at the end?
0
How many core and valence electrons does carbon have?
2 core, 4 valence
How sigma and pi bonds do the carbon atoms form in the diagram.
3 σ bonds and 1 π bond
What is the mass of 3.5 moles of Cl₂?
248 grams
CH₄(g)+2O₂(g)→2H₂O(l)+CO₂(g) How many molecules of CO₂ will be produced?
3
CH₄(g)+2O₂(g)→2H₂O(l)+CO₂(g) How many molecules of O₂ will remain at the end?
3
CH₄(g)+2O₂(g)→2H₂O(l)+CO₂(g) How many molecules of H₂O will be produced?
6
A)X has a longer stronger interaction than Y B)X has a shorter weaker interaction than Y C) X has a shorter stronger interaction than Y D) X has a longer weaker interaction than Y
A
Would you expect methane CH4 or difluoromethane (CF2H2 to have the higher boiling point? Why?
CF₂H₂ because it is a polar molecule that can form dipole-dipole interactions
What is a stable system formed at?
A potential minimum that would require energy input to change
What is wrong with the following statement? As the ball falls its potential energy decreases.
A single object cannot possess potential energy and there is no mention of a field
Which of the following contains the largest number of molecules?
A) 15.0 g Br₂ B) 15.0 g Cl₂ C) 15.0 g O₂ D) they all have the same number C) 15g O₂ because the mass of O₂ is the smallest so more O₂ molecules can fit into 15 g
Why do covalent bonds form?
Because electrons from one atom are attracted to the nucleus of another atom and the formation of a bond results in a stable system that would require the input of energy to change
If you put bromine liquid in a pan on the stove and heat it up, the bromine will boil. What is the mechanism (process) by which this happens?
As more bromine molecules get more energy, they can overcome the electrostatic forces of attraction and the bromine molecules can escape into the gas phase.
Thomson's plum pudding model
Argued that electrons are embedded in the atom although couldn't determine location of the electrons or if there were any other particles in the atom
If you put bromine liquid in a pan on the stove and heat it up, the bromine will boil. What is the mechanism by which the boiling process happens?
As more bromine molecules get more energy, they can overcome the electrostatic forces of attraction and the bromine molecules can escape into the gas phase
Thomson observed that the type of metal used for the cathode did not affect the behavior of the cathode ray. What claim does this piece of evidence support?
All atoms contain electrons
Which of these are true: I. All neutral atoms and molecules attract each others. II. London dispersion forces increase as the size of the electron cloud increases. III. It takes energy to overcome the attractions between particles. IV. Energy is released to the surroundings when atoms form a stable interaction.
All of these statements are true
Boron nitride is the second hardest substance known(after diamond). It has a very high melting point, but does not conduct electricity. What types of bonding do you think are present in boron nitride?
An extended network of boron and nitrogen atoms held together by covalent bonds
If the intensity of a beam of light is increased, this would correspond to:
An increase in the number of photons (considering light as a particle) and an increase in the amplitude of the wave (considering light as a wave)
An isolated helium atom is shown. In what state of matter is helium shown in this diagram?
An isolated atom doesn't exist in a state
The potential energy of the system as two atomic nuclei (eg H⁺) approach each other and fuse to form ²H?
At far distances, the nuclei are affected by the electrostatic force of repulsion, which causes the PE to increase as the distance decreases. Once the nuclei get very close to each other, the strong nuclear force takes over. This is an attractive force, which means the PE will decrease as the nuclei get closer to each other
Rutherford's planetary model
Atoms are composed of mostly empty space. His gold foil experiment showed that there are positively charged atoms because the foil deflected some of the alpha particles. He also noted that electrons orbit around the nucleus and eventually spiral out onto the nucleus
You are asked to compare the interaction between atoms of two substances, substance X and substance Y. When you look at the graph showing how potential energy changes as distance between the atoms changes, you notice that substance Y has a much deeper potential energy well than substance X. From this information, you conclude..
Atoms of Y interact to form covalent bonds and covalent bonds are stronger than London Dispersion forces and require more energy to break
Why do atoms start to repel each other when they become very close together?
Because the atoms are moving together despite the repulsive force (atoms are against the force), causing the PE to increase
Which of the following would you predict to have the smallest ∆Hvap? (The heat required to change one molecule of substance from a liquid phase to a gas phase (vaporize)? A)CH₃OH B)CH₄ C)OF₂ D)NaF
B)CH₄ because it only has LDFs which takes the least amount of energy to overcome
Which has the highest entropy (per mole)? A)H₂O(s) B)H₂O(g) C)H₂O(l) D) all have the same entropy
B)H₂O(g) -most arrangements can be made in the gas phase
if the same amount of thermal energy were transferred to equal masses of water, copper, granite and ethanol, which substance would reach the highest temperature? A)water(Cs=4.18J/g°C) B.Copper(Cs=0.385J/g°C) C.Granite(Cs=0.7 J/g°C) D.Ethanol(Cs=2.42J/g°C) E. they would all reach the same temperature since an equal amount of thermal energy is transferred to an equal mass of each
B.Copper(Cs=0.385J/g°C) because it has the smallest amount
Yellow light ejected electrons from a piece of potassium metal. If the metal in the photoelectric effect experiment changed to lithium, what type of light would you predict is needed to eject the electrons?
Blue light because the valence electron in Li is closer to the nucleus than the valence electrons in K. Li would need a higher energy photon to overcome the stronger force of attraction.
2 ¹²C→²³Mg+¹n+energy What is this reaction an example of?
a nuclear fusion reaction because small nuclei are coming together to make a larger nucleus
Which do you predict to have a higher boiling point and why? CH₃OH CH₃CH₂CH₂OH
CH₃CH₂CH₂OH because the london dispersion forces are stronger because the molecule is larger, so more energy is required to overcome them
Which of the following substances would you expect to have the highest boiling point? I)CH₃CH₂NH₂ II)CH₃CH₂CH₃
CH₃CH₂NH₂ because the strongest attractive force that is over is hydrogen bonding
Fluorine (F₂) and Chlorine (Cl₂) both exist as diatomic molecules. Fluorine has a boiling point of 85.03K, and chlorine has a boiling point of 239K. Draw a graph showing the change in PE as two molecules of fluorine and chlorine get closer to eachother
Chlorine has a stronger interaction than fluorine because chlorine has a greater mass which creates a greater intermolecular distance and higher boiling point
Rutherford's experiment
Claim: the atom is mostly empty space with a very small dense nucleus Evidence: Most alpha particles went straight through, only a few were deflected Reasoning: the positively charged alpha particles were deflected by the repulsive interaction with the positive nucleus; since only a few were deflected the nucleus must take up a very small volume of the atom
Which do you think will have a higher boiling point and why? -Cl₂ -F₂
Cl₂ because the LDFs between molecules are stronger, requiring more energy to overcome
Which is the smallest? A) an atom B) a cell C) a proton D) an electron
D) an electron
A substance has a low melting point. It does not conduct electricity either when melted or as a solid. It is most likely: A)diamond B) copper C)Calcium oxide D)paraffin (C₃₁H₆₄)
D) paraffin (C₃₁H₆₄) because only LDF are present
When two nuclei move extremely close to each other (within the distance of nucleus), the potential energy....
Decreases because the strong nuclear force between the nuclei is attractive
Consider a container of xenon atoms where two xenon atoms of interest are interact (the system) and are surrounded by other atoms. The surrounding Xenon atoms have more energy than the two xenon atoms in the system. Which direction would you predict the energy would be transferred and what would happen?
During a collision, energy will be transferred from the surrounding xenon atoms to the system of two xenon atoms and the stable interaction will be overcome.
What wavelength of light would break an O=O bond (it takes 8.3x10⁻¹⁹J to break one O=O bond)?
E=hv 8.3x10⁻¹⁹J=6.626x10⁻³⁴(v) v=1.2526x10¹⁵Hz 3.0x10⁸m/s=1.2526x10¹⁵Hz(λ) λ=2.4x10⁻⁷m λ=2.4x10⁻⁷m(10⁹nm)=240nm
Thomson's cathode ray tube experiment showed that the beam of emitted particles was deflected by charged particles. Thomas used this evidence to support his claim that:
Electrons carried an electrical charge
Thomson's experiment allowed him to make the claim that all atoms have a sub structure and contain smaller particles (electrons) embedded in the structure of the atom. What evidence and reasoning allowed him to make this claim?
Evidence: Electrons were ejected from the cathode, regardless of what metal the cathode was made of. Reasoning: Since the particles are emitted regardless of the nature of the nature of the cathode, they must be part of the sub-structure of the atom
Elements are composed of small indivisible, particles called atoms
False, atoms have a substructure
Which reaction requires the most energy?
F⁺→F²⁺+e⁻ (higher Zeff, so harder to remove electron) -Effective nuclear charge(Zeff)=# of protons-# of core electrons -when electrons are reduced, the repulsion b/w the electrons decreases=decrease in the radius which causes the strength of the attraction to increase in the amount of energy to remove an electron
Rank of electromagnetic radition
High energy: gamma-ray, x-ray, UV, visible, IR, microwave, long wave: low energy
Dalton's billiard ball model
His model of the atom consisted of a solid nucleus with no electrons. Photons are reflected off the atom.
Which of the following are correct statements? I)Covalent bonds are interactions within molecules II)Covalent bonds are interactions between separate molecules III) LDFs are interactions between separate molecules IV) LDFs are within molecules
I)Covalent bonds are interactions within molecules III) LDFs are interactions between separate molecules
Which diagram best represents the band structure for sodium and can be used to explain its electrical conductivity?
I, because sodium conducts electricity because electrons can move freely into empty molecular orbitals
Which diagram best represents the band structure for sodium (Na) and can be used to explain its electrical conductivity?
I, sodium conducts electricity because electrons can move freely into empty molecular orbitals
Which of these are true: I. Covalent bonds are interactions within molecules II.Covalent bonds are interactions between separate molecules III. LDFs are interactions between separate molecules IV. LDFs are within molecules
I. Covalent bonds are interactions within molecules III. LDFs are interactions between separate molecules
Three methanol molecules are shown. Which of the labeled interactions are hydrogen bonding interactions
II only
Which of the following would you expect to have a measurable melting point? I) an isolated atom II) a 5 gram block of gold III) both I and II have measurable melting points
II) A 5 gram block of gold because in order to melt, there must be more than one particle present so that the forces between the particles can be overcome
Two lewis structures are shown. Are these molecules the same or are they isomers?
Isomers because the molecules have the same formula but different atom connectivity
The boiling point of iodine (I₂)is much higher than the boiling point of helium (He). Why?
I₂ has a larger electron cloud than He, so more energy is required to overcome the stronger London Dispersion Forces
Which of following substances conducts electricity in the liquid state, but not the solid state? KBr or Na
KBr because charged ions are free to move relative to one another in the liquid state but not the solid state
Opposite charges are attracted to each other in proportion to the product of their charges and inversely proportional to the square of the distance between them. This statement is a...
Law because it describes the phenomenon
When oxygen boils...
London dispersion forces between the O₂ molecules are overcome
Consider the following four objects: M1=5g M2=5 g M3=10 g M4=10 g Assume that the objects are separated by equal distance. Between which two objects is the gravitational force the strongest?
M3 and M4
The first six ionization energies for an element in the third period are shown in the graph. Which element is this?
Mg -b/c the biggest change is between the 2nd and 3rd ionization energies and magnesium is the 2nd element in the third period. You always pick the element that comes first when the jump occurs.
Which has a larger atomic radius? Mg or Ar and why?
Mg, because its valence electrons are not as strongly attracted towards the nucleus as those in Ar. The Zeff on Mg is smaller. On Ar the electrons are more attracted causing the cloud to shrink until e-e repulsions come into effect
What is most likely the formula for a compound between magnesium and bromine?
MgBr₂ because Mg²⁻Br⁺¹ and flip numbers
Consider the isoelectronic (they all have the same number of electrons) species Na⁺, Mg²⁺,Ne, F⁻. Which of these has the smallest radius?
Mg²⁺ (highest proton to electron ratio and highest Zeff) -they all have the same electrons but different number of protons -Zeff(effective nuclear charge)=# of electrons- # of core electrons -atoms with a high ENC hold on to their atoms more tightly which is why electrons are strongly attracted to the nucleus
For a gas at room temperature..
Molecules are moving at different speeds because collisions transfer energy between molecules
Which of the following compounds would most likely have the higher melting point, NaF or CsBr? Why
NaF, because the ions are smaller making the attraction between them stronger so that more energy is required to overcome these interactions
A molecular orbital diagram for B is shown to the right. Will Be exist as a molecule according to molecular orbital theory?
No because electrons in bonding orbitals make the species more stable and electrons in antibonding orbitals make the species less stable and the stabilization form the electrons in bonding molecular orbitals is cancelled out by the destabilization caused by the electrons filling the antibonding molecular orbitals
Glucose (C₆H₁₂O₆, molar mass 180g/mol) reacts with oxygen (O₂, molar mass 32 g/mol) to produce carbon dioxide (CO₂, molar mass 44g/mol) and water (H₂O, molar mass 18g/mol). C₆H₁₂O₆→6CO₂+6H₂0 During this reaction 10g of C₆H₁₂O₆ reacts with excess oxygen to produce 8g of water. Evaluating the percent yield you obtained for this reaction, is this a good yield if you were expecting to get an 80 to 90% yield for the reaction?
No this is not a good yield because there is more product than could possibly be formed and so there must be an impurity in it.
A molecular orbital diagram for beryllium (Be) is shown. Will beryllium exist as a molecule according to molecular orbital theory?
No, electrons in bonding orbitals make the species more stable and electrons in antibonding orbitals make the species less stable and the stabilization from the electrons in bonding molecular orbitals is cancelled out by the destabilized caused by the electrons filling the antibonding molecular orbitals
Consider the elements sulfur and oxygen. Which element is more electronegative? O or S
O, because the bonding electrons are closer to the nucleus
For a given photocell (a device that uses the photoelectric effect to generate electricity), blue light will eject electrons but red light will not. Why?
Photons of blue light each have enough energy to eject one electron
Iodine exists as molecules of I₂, and silicon dioxide exists as an extended network of silicon oxygen bonds (similar to diamond). They both are solids at room temperature, but which do you think has the higher melting point and why?
Silicon dioxide, because it is a compound
Which piece of evidence supports that claim that all matter and energy in the Universe were once concentrated in a single point (singularity)?
The absorption spectra of galaxies are red-shifted because those galaxies are moving away from us
In Rutherford's gold foil experiment, the majority of the alpha particles went straight through the gold. Why was that?
The atom is mostly empty space, so nothing manipulated the path of the alpha particles
Why do two isolated atoms attract each other as they approach and why do they repel if they get too close together?
The attractive coulombic interaction causes thee atoms t approach due to the partial positive and negative sides of atom created by instantaneous dipole however once the atoms get too close the atoms begin to overlap and the atoms create a repulsive force and repel
What causes the change in potential energy when the two helium atoms move from point Z to point Y in the figure?
The attractive force
What can we use to predict whether atoms interact through covalent bonds or ion-ion interactions (ionic bonding interactions)?
The electronegativity difference between the atoms -if the atoms have similar electronegativities, valence electrons will be shared between nuclei. When the electronegativities are very different, the valence electrons will be completely transferred from the less electronegative atom to the more electronegative atom
How would the strength of the electrostatic force change if the distance between two charged objects increased?
The electrostatic force would become weaker
How would the energy change as two helium atoms move from point Z to point Y in the figure?
The kinetic energy increases, the potential energy decreases, the total energy doesn't change
Helium exists at room temp as a monatomic gas(He) and hydrogen exists in room temperature as a diatomic gas (H₂)...
The number of molecules in one mol of H₂ is greater than the number of atoms in one molecule of He
Compare a 3s orbital to a 3p orbital
The orbitals have different shapes and different energies
The potential energy as two positive atoms approach each other and why does the potential energy change in the way shown
The positive charges are moving toward each other against the repulsive force that exists between them
What happens on the molecular level when thermal energy (heat) is added to increase the temperature of water from 10°C to 50°C?
The water molecules speed up, and collide with the thermometer, transferring energy to the thermometer. this energy causes the mercury atoms in the thermometer to vibrate more, and the liquid expands (thus showing an increase in the temperature scale)
One part of Dalton's Atomic Theory states: Compounds are formed by combinations of atoms from two or more elements
This is true because by definition a compound must have at least two types of elements
Water (H₂O) and dihydrogen monosulfide (H₂S) have similar chemical formulas and structure. At room temperature, H₂O is a liquid and H₂S is a gas. What is the difference?
Water is more polar and thus the attractive forces between water molecules are stronger than the attractive forces between H₂S molecules.
isomers
What is the same: number of each type atom and chemical formula What is different: connectivity b/w atoms and properties
When and where were the carbon and oxygen atoms in your body created?
Within stars and stellar explosions
Consider the following velocity distributions for different gases at the same temperature. Which gas has the smallest velocity? A) Ne B) Ar C) Kr D) Xe
Xe- because it has the largest mass which causes a decreases in velocity
Does the planet Venus have phases like the moon? Is this question a scientific question?
Yes because it can be tested and answered through observations and experiments.
Can graphite conduct electricity?
Yes, graphite exists as 2D sheets of sp² hybridized C atoms. Unhybridized p orbitals can interact to form delocalized pi orbitals that extend throughout the sheet. Electrons in the pi network can move freely.
In the lab you mix together 10g of 10g of ammonia with 15g of oxygen to form nitric oxide with water. You are asked to produce 25g of nitric oxide (NO). Do you have enough starting materials to produce the desired amount of NO and why? Also what is the maximum amount of (in grams) of nitric oxide that would be produced during this reaction?
You must change 10g NH₃ to g of NO and 15g O₂ to g of NO and then determine which is the limiting reactant -there is not enough of either reactant to produce 25g of NO -11.3 g NO is the maximum amount that can be produced
What is the electron configuration of Se
[Ar] 4s²3d¹⁰4p⁴
When a covalent bond is formed between two atoms
a collision must happen to transfer energy out of the system
How many core and valence electrons does magnesium (Mg) have?
a) 10 core and 2 valence
What could you use as evidence to support the claim "energies of electrons are quantized"?
absorption and emission spectra
percent yield
actual/theoretical x100
Which part of Dalton's theory can be proven false by the existence of isotopes?
all atoms are indivisible and indestructible
As two isolated He atoms approach eachother
as they approach KE↑ then ↓ PE↓ then ↑ sharply
Atomic radius trend
atomic radius ↓ across row atomic radius ↑ down a group ↑electrons, ↑radius
electrostatic/electromagnetic
attractive and repulsive force -requires two or more objects
London dispersion forces and covalent bonds are both...
attractive interactions and they both release energy when they are formed
Why is nuclear fusion not a viable option for generating energy at the moment?
because of the high energy requirement to overcome the coulombic repulsion of the nuclei
why do bonds form between atoms?
because the electron(s) on one atom are attracted to the nucleus of the other atom. When the attractive force equals the repulsive force (PE minimum), the bond is formed
nuclear fission
breaking a nuclei apart, neutrons released in fission can induce more fission (splitting of large atom into 2 or more smaller ones
What is the wavelength of light that has a frequency of 3.0x10⁹Hz?
c=λv C=3.0x10⁸m/s 3.0x10⁸m/s= 3.0x10⁹Hz(λ) λ=0.1m=10cm
open system
can transfer energy and matter (biological system) -a person eating a sandwich
Why do ionic compounds conduct electricity in the liquid state, but not in the solid state?
charged ions are free to move relative to one another in the liquid state
What is the best explanation as to why copper is ductile (can be pulled into wires)?
delocalized electrons hold the copper together as the nuclei move relative to each other
Identify the types of intermolecular forces present in the diagram
dipole-dipole and london dispersion forces -the molecule is polar because oxygen is the most electronegative (it is the farthest to the right)
Atomic absorption spectra are caused by:
electrons moving to higher energy levels and absorbing photons of energy equal to the energy difference between the levels
radioactive decay
emitting particles, nucleus emits or captures particles or energy in the form of electromagnetic radiation
moving from solid→liquid→gas
energy is absorbed
moving from gas→liquid→solid
energy is released
specific heat capacity
energy required to raise 1 g by 1°C (or 1K) -higher specific heat=more energy required to raise temp -how much energy it takes to change the energy of a substance
molar heat capacity
energy required to raise 1 mol by 1°C (or 1K)
theory
explains the phenomenon tells you WHY
The atomic theory of matter is an example of a scientific theory. What distinguishes it from a scientific law such as the law of gravity? The atomic theory:
explains the underlying cause of a range of phenomena
atoms that are compounds
false, not possible
The boiling point of hydrogen is 20K. Describe the particles present in a container of hydrogen at 25K
gaseous hydrogen molecules
Enthalpy H
heat absorbed or emitted during a reaction under constant pressure
Relationship between wavelength, frequency and velocity
higher frequency=higher velocity=shorter wavelength
Which of the follo transitions would be most likely to result from the absorption of a photon of the highest frequency?
highest frequency=highest energy -largest change in energy for absorption is the longest upward arrow.
Hydrogen bonding
hydrogen can only bond with N, O, F -has to have an interaction with lone pair
As two protons move toward each other, the potential energy of the system will...
increase because of the repulsive force between the like charges
relationship of LDF
increase the size of atom then increase in LDF and when you increase the size it is harder to break the bonds
If a reaction occurs between a compound that has a lemon smell and one that has a rose smell what will the product smell like?
it is impossible to predict the smell of the product because the properties of the new substances depends on its molecules structure (the properties are emergent)
A property of metals at the atomic level is described below. Which property does describe? "Metal atoms are packed in layers that can move relative to one another. When the nuclei move relative to one another, the valence electrons act as a glue holding them together."
metals are ductile
Consider the photoelectric effect experiment. In one experiment, yellow light shines on a piece of potassium metal. A current is measured, meaning electrons are ejected from the potassium metal. What would happen if the intensity of the yellow light increased?
more electrons would be ejected because increasing the intensity increases the number of photons
Does one molecule of water have a boiling point?
no because the boiling point is the temperature at which the particles change from liquid to gas. If there is only one particle the words liquid and gas (and solid for that matter) are meaningless
isolated system
no transfer of matter or energy (an insulated closed container-hard to do) -soup in an isolated container
does one molecule of water have a boiling point?
no, because the boiling point is the temperature at which the particles change from liquid to gas. If there is only one particle the words are liquid and gas (and solid for that matter) are meaningless
What kind of reaction is this? 4¹H→⁴He+2+₁e
nuclear fusion -e for energy 4 small hydrogen atoms make 1 large He atom
How to calculate thermal energy changes
q=m x c x ∆T =mass(specific heat)(temperature change)
The internuclear distance between two neon atoms compared to the internuclear distance between two krypton atoms where both systems are the most stable is..
smaller because neon has a smaller electron cloud
The boiling point of neon is -246°C and the melting point of neon is -249°C. What state is neon at -260°C?
solid
What is the driving force for bond formation?
the attraction between electrons of one atom and the protons of the other
At what point on the curve are the atoms most stable?
the curve represents the potential energy changes as the distance changes as the distance between two hydrogen atoms changes. Y, because the attractive and repulsive forces are balanced
What is the cause of the attractive force between the two He atoms?
the electron clouds of the He atoms may fluctuate randomly causing a transient dipole that induces a dipole in other atoms which causes them to attract each other.
Consider a system where two helium atoms are approaching from a distance. Two atoms approach and get close enough so that their electron clouds overlap. Why does the potential energy increase?
the electron clouds repel each other
what causes the formation of covalent bonds between atoms?
the electrons on one atom are attracted to the protons on another atom
A calculator on your desk will not move because..
the electrostatic force is equal to the force of gravity
ioniozation energy
the minimum amount of energy required to remove a valence electron
In an isolated system, when two atoms collide...
the total potential energy of the system will not change
What is the best explanation for a pattern such as those obtained when X-Rays are diffracted by crystals?
the waves of electromagnetic radiation arrive in-phase and out of phase at the detector
If the mp/bp is higher then...
there is a stronger interaction present
closed system
transfer energy but not matter (a closed container) -milk carton
molecules that are elements
two or more of the same atom
double slit experiment
waves crisscross & create light on the screen and where they cancel out if where there is darkness
Consider a system where two helium atoms are approaching from a distance. The distance between the two helium atoms where the system would be the most stable is:
where the potential energy is at a minimum
destructive interference
where the two waves are out of phase and cancel out which creates darkness
constructive interference
where two waves in a phase intensifies the light
What is the wavelength of an electron travelling at 5.01 x 10⁵ m/s? The mass of an electron is 9.1 x 10⁻³¹ kg.
λ=h/mv λ=6.626x10⁻³⁴/5.01x10⁵(9.1x10⁻³¹) =1.45x10⁻⁹m
