Unit 1: Atoms Flashcards
What is conservation of mass?
atoms (or mass) cannot be created nor destroyed
total mass in a chemical reaction remains unchanged
What is meant by constant composition?
compounds result from a combination of a specific ratio of different elements
example: CCl4 will always have 1 carbon and 4 chlorine
What is meant by multiple proportions?
two or more elements combine together to form several different compounds
example: H and O can form H2O or H2O2 depending on how many atoms are present
What experiments showed that atoms are made up of smaller particles?
J.J. Thomson’s cathode ray experiment
Millikan’s oil drop experiment
What is a nucleus?
very dense
contains a small positive charge
protons + neutrons
What is electron density (electron cloud)?
very light
form bonds
responsible for chemistry
What are isotopes?
atoms of a given element can have different masses due to different number of neutrons
What happens when an atom has a different number of protons?
different elements
What happens when an atom has a different number of electrons?
ions
What is quantum theory and atomic structure?
periodic properties of the elements come from atomic structure
Rutherford’s nuclear model is inadequate
our current model is based on quantum theory, which arose out of experiments on the nature of light and matter
What is matter?
particulate (comes in chunks)
travels on definite paths
What is energy?
continuous
spreads out in all directions “wave-like”
What is frequency?
cycles per second
units of s^-1 or Hz
What is wavelength?
the distance a wave travels in one cycle
units of length (m, nm)
What is amplitude?
the height of a wave crest or depth of a trough
maximum displacement of the wave
What is refraction?
bending of waves
What is diffraction?
interference of waves
What experiments showed that light also has particulate properties?
Blackbody Radiation
Photoelectric Effect
Atomic Spectra
What is Blackbody Radiation?
a solid object emits visible light when it is heated to about 1000K
EM radiation emerging from a blackbody gives a spectrum that cannot be explained by treating light as a wave
higher temperature = higher intensity of light
What is the Photoelectric Effect?
when monochromatic light shines on a metal surface, electrons are ejected
E = hc/wavelength
number of electrons emitted is dependent on the intensity of the light
minimum frequency of light needs to be reached
What is Atomic Spectra?
when atoms of a vaporized element absorb energy (such as in an electrical discharge tube), they emit light to give a discontinuous line spectrum
spectral lines are produced when an electron moves from one energy level to another
What is Bohr’s Model of the hydrogen atom?
the electron can only occupy certain stationary states, with fixed energies
the electron does not lose energy (in the form of radiation) while in a stationary state
the electron undergoes a transition from one stationary state to another by absorbing or emitting photons
What is the absorption of an electron?
excitation from a lower allowed energy level to a higher allowed energy level
What is the emission of an electron?
relaxation from a higher allowed energy level to a lower allowed energy level
What is wave-particle duality?
both matter and energy can exhibit both particle and wave-like behavior
What is the wavelength of the H atom?
Schrodinger (1927) developed a theory called quantum or wave mechanics to describe particles (such as electrons) as waves
What are the different ways to depict the probability of finding the electron in a H atom?
electron density: snapshots at different times, further away from the nucleus less likely to have an electron, r never reaches 0
radical probability distribution: count the dots in each section/sample
boundary surface: enclosure of 90% electron density
What is the principal quantum number?
symbol: n
allowed values: 1, 2, 3, …
interpretation: govern the energy and size
What is the angular momentum quantum number?
symbol: l
allowed values: 0, …, n - 1
interpretation: indicates shape
What is the magnetic quantum number?
symbol: ml
allowed values: -l, …, +l
interpretation: governs orientation
What are the different shapes of hydrogen orbitals?
s orbitals (l = 0) are spherical p orbitals (l = 1) are dumbbell shaped d orbitals (l = 2) are clover shaped
What are many-electron atoms?
in atoms containing more than one electron (many-electron species), the presence of electron repulsion causes the energy of the orbitals to vary in a complicated way
How do orbital energies differ in one vs. many electron atoms?
in one electron atoms the orbitals all have the same amount of energy
in many electron atoms the orbitals don’t have the same amount of energy
What factors affect orbital energy?
- Effect of nuclear charge
- Effect of electron-electron repulsions
- Effect of orbital shape
- A fourth quantum number
How does the nuclear charge effect orbital energy?
greater nuclear charge lowers orbital energy
How does electron-electron repulsions effect orbital energy?
electron-electron repulsions increase orbital energy
electrons in outer orbitals (higher n) are shielded from the full nuclear charge, so they have higher energy
How does orbital shape effect orbital energy?
orbitals with good penetration (having electron density close to the nucleus) have lower energy
What is the fourth quantum number?
spin
symbol: ms
allowed values: +1/2, -1/2
interpretation: spin up or spin down
How do you determine electron configurations?
- Add electrons successively into lowest energy orbitals upward
- Observe Pauli Exclusion Principle
- Observe Hund’s Rule
What is the Pauli Exclusion Principle?
states that “no two electrons can have all four quantum numbers alike”
each orbital can be occupied by a maximum of two electrons of opposing spin
What is Hund’s Rule?
when orbitals of equal energy are available, maximize unpaired spins
What trends do electron configurations for transition metal ions follow?
tend to lose valence electrons to form cations
transition metal atoms can form several cations, with the ns electrons being removed before the (n-1)d electrons
What does paramagnetic mean?
attracted to an external magnetic field
contains unpaired electrons
What does diamagnetic mean?
weakly repelled by magnetic field
all electrons are paired
How do we define the size of an atom?
atomic radius = 1/2 distance between two nuclei
How do we compare ionic radii?
cations are smaller than atoms
anions are larger than atoms
What is ionization energy?
the energy that must be added to remove an electron from an isolated gaseous atom or ion
What is electron affinity?
the energy change that occurs when a gaseous atom or ion gains an electron
What are the trends of properties down a group?
effective nuclear charge is constant
radius increases
ionization energy decreases
electron affinity becomes less negative
What are the trends of properties across a period?
effective nuclear charge increases
radius decreases
ionization energy increases
electron affinity becomes more negative
What are properties of metals?
have low ionization energy and less negative electron affinity
tend to lose electrons readily
What are properties of nonmetals?
have high ionization energy and more negative electron affinity tend to gain electrons
What happens to the reducing agent in a redox reaction?
loses electrons
is oxidized by the oxidizing agent
oxidation number increases
What happens to the oxidizing agent in a redox reaction?
gains electrons
is reduced by the reducing agent
oxidation number decreases
Are alkali metals good oxidizing or reducing agents?
good reducing agents because they easily lose electrons
Are halogens good oxidizing or reducing agents?
good oxidizing agents because they easily gain electrons
What are characteristics of good reducing agents?
easily lose electrons
are in an “unusually low” oxidation state
What are characteristics of good oxidizing agents?
easily gain electrons
are in an “unusually high” oxidation state
What is the behavior of oxides in water?
metal oxides give basic solutions
nonmetal oxides give acidic solutions
What are the best uses of hydrogen for fuel?
- Haber process: cheapest method to produce ammonia
- Hydrogenation reactions: unsaturated to saturated
- An alternative fuel to hydrocarbons
What are the advantages to using hydrogen as a fuel?
cleaner (no CO2 produced)
on a per gram basis combustion of H2 releases more energy
What are the disadvantages to using hydrogen as a fuel?
no cheap source of hydrogen
difficult to transport and store H2
What do each of the letters mean in the A, Z, X notation?
A is on top and it’s the atomic mass number
Z is on the bottom and it’s the number of protons
X is the element symbol
How do you calculate the natural abundance of isotopes?
Let one percentage equal x and the other equal (1 - x)
Then use the formula:
atomic mass of atom = atomic mass of isotope(x) + atomic mass of isotope(1 - x)
What is the name of the polyatomic ion ClO4?
Perchlorate
What is the name of the polyatomic ion IO?
Hypoiodite
What is the name of the polyatomic ion Cr2O7?
Dichromate
What is the name of the polyatomic ion CH3COOH?
Acetate
What is the name of the polyatomic ion PO3?
Phosphite
What is the name of the polyatomic ion NH4?
Ammonium
What is the name of the polyatomic ion HCO3?
Bicarbonate
What is the name of the polyatomic ion CN?
Cyanide
What is the name of the polyatomic ion HSO4?
Hydrogen sulfate
What is the name of the polyatomic ion NO3?
Nitrate
What is the name of the polyatomic ion NO2?
Nitrite
What is the name of the polyatomic ion MnO4?
Permanganate
What is the name of the polyatomic ion CO3?
Carbonate
What is the name of the polyatomic ion CrO4?
Chromate
What is the name of the polyatomic ion HPO4?
Hydrogen phosphate
What is the name of the polyatomic ion SO4?
Sulfate
What is the name of the polyatomic ion SO3?
Sulfite
What is the name of the polyatomic ion S2O3?
Thiosulfate
What are two formulas associated with energy, wavelength, and frequency?
E = hc/wavelength
f = c/wavelength
What is the relationship between energy and wavelength?
Longer wavelength corresponds to smaller energy
What is the definition of shielding?
Refers to the effect that other electrons, especially the inner-shell electrons, have in reducing the full nuclear charge actually felt by an outer-shell electron
What is the definition of effective nuclear charge?
The net positive charge acting on a particular atom
It’s value is the charge on the nucleus, reduced to the extent that other electrons screen the particular electron from the nucleus
What is penetration?
Refers to the occurrence of a probability distribution such that an electron can be found close to the nucleus part of the time,
it’s effect is to counteract the shielding of inner electrons so that the orbital experiences a greater than expected effective nuclear charge and is thereby stabilized
