MCAT Physical Sciences Flashcards
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- What is an atom?
- The smallest unit of a chemical element.
- What are the three main subatomic particles?
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1. Proton
2. Neutron
3. Electron - What are orbitals?
- Characteristic regions of space outside the nucleus of an atom where electrons exist.
- What is an element?
- Substance that show similar chemical properties and can't be broken down further than the atomic level by chemical means.
- What are protons?
- Subatomic particles that carry a positive charge and have a mass of approximately one atomic mass unit (AMU).
- What is the atomic number (Z)?
- The number of protons found in an atom of that element.
- What are neutrons?
- Subatomic particles that carry no charge and have a slightly larger mass than protons.
- What are isotopes?
- Elements with the same atomic number, but different numbers of neutrons.
- What is the mass number of an atom?
- The total number of protons and neutrons.
- What are electrons?
- Subatomic particles that carry a single negative charge and are 1/1,837 th the mass of a proton.
- What are valence electrons?
- The electrons farthest from the nucleus.
- What role does distance from the nucleus play with valence electrons?
- The further away from the nucleus the valence electrons are, the weaker the attractive force of the positively charged nucles and the more likely the valence electrons are to be influenced by other atoms.
- What role do valence electrons play in chemical reactions?
- The activity of the valence electrons determine the reactivity of a chemical.
- What are the general characteristics of a neutral atom?
- The number of protons is equal to the number of electrons.
- What is an ion?
- An atom with a positive or negative charge due to a difference in the number of electrons from the number of protons.
- What is the standard for determining atomic mass?
- The carbon-12 atom, defined as exactly 12.000 AMU.
- What is the atomic weight?
- The weight in grams of one mole of a given element.
- What is a mole?
- 6.022 x 10^23 of something.
- What is Avogadro's number?
- 6.022 x 10^23
- What is quantum theory?
- The theory that states that energy emitted from matter as electromagnetic radiation comes in discrete bundles.
- What are quanta?
- The discrete bundles of electromagnetic radiation emitted from matter.
- What equation gives energy value of a quantum of energy?
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Planck's equation:
E = hv
where h is Planck's constant
E is energy and
v is frequency - What accounts for the majority of the volume of the atom?
- Empty space.
- How does the Bohr model of the atom equate angular momentum to quantum theory?
- The Bohr model states that the angular momentum of an electron can only occur in quantized (discrete) amounts.
- What is the equation for angular momentum of an electron?
-
Angular Momentum = nh/2(pi)
where n is the quantum number
h is Planck's constant (6.626 x 10^-34 J/s. - What is the relationship between quantum number and angular momentum in the Bohr model?
- The angular momentum can only change in discrete amounts, based on the quantum number, which can only be a positive integer.
- What is equation is derived from the relationship between quantum energy and angular momentum?
-
E = -RH/n^2
where E is energy
RH is the Rydberg constant (2.18 x 10^-18 J/electron - Why is there a negative sign in the E = -RH/n^2 equation?
- Value of zero energy was assigned to the situation when the electron was completely separated from the proton. Therefore, the electron in any of its quantized states in the atom would have a negative energy because of its attraction to the proton.
- What does quantized mean?
- The energy of an electron can only exist in certain fixed amounts.
- What generalizations can be made from the Bohr model of the atom?
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1. The energy of the atom is directly related to its orbital radius. (The smaller the radius, the lower the energy state).
2. Explains atomic emission spectra. - What is the ground state energy level?
- The lowest energy state of an electron, where the quantum number equals 1.
- What happens when excited electrons return to their ground state energy level?
- They emit energy in the form of photons.
- What equation is used to determine the amount of energy released when electrons return to their ground state energy level?
-
E = hc/lamda
where E is energy
h is Planck's constant (6.626 x 10^-34 J*s)
c is the speed of light (3.00 x 10^8 m/s)
lamda is the wavelength of the photon emitted - What is a line spectrum?
- Spectrum of light when electrons emit a photon at distinct wavelengths.
- What is the atomic emission spectrum?
- The spectrum of light emitted electrons of different atoms of elements, which uniquely identifies the element?
- Why are atomic emission spectra unique to the element?
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1. Because different electrons in an atom will be excited to different energy levels.
2. and because each atom has a different configuration of electrons. - What is the Balmer series?
- The group of hydrogen emission lines corresponding to transitions from n>2 to n=2, has 4 wavelengths in the visible region.
- What is the Lyman series?
- The group of hydrogen emission lines corresponding to transitions from n>1 to n=1, they are higher energy transitions and occur in the UV region.
- What relationship exists between the change in quantum number and the energy of an emitted photon?
- The energy associated with the difference between the initial quantum number and the final quantum number is equal to the energy of the emitted photon.
- What is the equation for the relationship between photon emission and change in quantum number?
- E = hc/lamda = -RH[1/(ni^2)-1/(nf^2)]
- How does the Bohr model explain atomic absorption?
- Since the amount of energy needed to promote an electron to the next energy level is discrete, energy will be absorbed at specific wavelengths.
- Where does the Bohr model fail to explain atomic behavior?
- When there is more than one electron in an atom.
- Why does the Bohr model fail when there is more than one electron?
- Because it doesn't account for the repulsion between electrons in orbit.
- What is the most important difference between the modern quantum mechanical model and the Bohr model?
- The assumption that electrons travel in a circular orbit around the nucleus is no longer considered valid.
- What does an orbital represent?
- The probability of finding an electron within a given region.
- What is the Heisenberg uncertainty principle?
- It is impossible to determine with perfect accuracy the momentum and position of an electron simultaneously.
- What are the four quantum numbers?
- n, l, m sub l, m sub s.
- What is the Pauli exclusion principle?
- No two electrons in a given element can have the same set of four quantum numbers.
- What is the energy state?
- The position and energy of an electron as described by the four quantum numbers.
- What is the principle quantum number (n)?
- The quantum number used in the Bohr model, and can be any positive integer.
- What is the relationship between principle quantum number and orbital size.
- There's a direct relationship between them. The larger the principle quantum number, the larger the orbital.
- What is the relationship between the energy difference between shells and their distance from the nucleus?
- The farther away from the nucleus, the less energy needed to promote the electron to the next energy level (e.g. the amount of energy from n=3 to n=4 is much less than n=2 to n=3.)
- What is the azimuthal (angular momentum) quantum number (l)?
- The quantum number that refers to subshells (sublevels) that occur within each principal energy level.
- What is the relationship between principle quantum number and azimuthal quantum number?
- The azimuthal quantum number can be any number between zero and one less than the principal quantum number. The principle quantum number limits the azimuthal quantum number.
- What l-values correspond to the s, p, d, and f subshells, respectively?
- 0,1,2,3
- What is the equation for maximum number of electrons that can occupy a subshell
- 4l + 2
- What exceptions occur when electrons fill the different subshells?
- The energies of the different subshells can overlap, because of increased distance from the nucleus. (e.g. 4s has lower energy level than 3d because its closer to the nucleus)
- What is the magnetic quantum number?
- The quantum number that specifies the particular orbital within a subhshell where an electron is highly likely to be found at a given point in time.
- What are the possible values for m sub l?
- All integers from -l to +l including 0.
- What formula can be used to determine the total number of m sub l values for a particular l value?
- 2l+1
- What is the formula for the number of m sub l values from an n value?
- n^2.
- What is the spin quantum number?
- The number that denotes its intrinsic angular momentum.
- What are the values for the m sub s?
- + 1/2; -1/2
- What are the rules for the value of m sub s for two electrons in the same orbital?
- Two electrons in the same orbital cannot have the same m sub s value.
- What are parallel spins?
- Two electrons in different orbitals with the same m sub s value.
- What is the n + l rule?
- The lower the values of the first and second quantum numbers, the lower the energy of the subshell. If two subshells possess the same (n + l) value, the subshell with the lower n value will fill furst.
- What is the order in which the subshells fill?
- 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
- What is Hund's rule?
- States that within a given subshell, orbital s are filled such that there are a maximum number of half-filled orbitals with parallel spins.
- What are paramagnetic materials?
- Materials whose atoms have unpaired electrons in orbitals; they are attractd to a magnetic field.
- What are diamagnetic materials?
- Materials whose atoms are paired up in their orbitals; they are slightly repelled by a magnetic field.