GCHEM
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- The geometry or shape of a molecule refers to positions of atoms/electron pairs/both?
- ONLY positions of atoms
- An element which can act as an electron acceptor should have a high or low electron affinity? metal or non-metal?
- high electron affinity, non-metal (like S)
- Acid vs. Base
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Acid: Arrhenius- a substance that ionizes in water to produce protons
Bronsted-Lowry- a substance that donates a proton to some other substance
Lewis- electron pair acceptor
Base: Arrhenius- a substance that ionizes in water to produce hydroxide ions
Bronsted-Lowry- a substance that accepts a proton from some suitable donor
Lewis- electron pair donor - First ionization energy
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the energy required to remove an electron from the outer shell of an atom
-low value: when removal of e- yields a complete shell
-high value: when removal of e- disrupts a complete shell - Mass Number= ___ + ____
- protons + neutrons in the nucleus
- How do you calculate a half life?
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original amount/final amount=#
2^ what power= #
power= # half-lifes
#half-lifes * # yrs in one half life= # yrs that pass - Nucleons
- Protons & Neutrons
- Atomic Number
- # Protons in nucleus
- Mass Number
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# Protons + # Neutrons
* sometimes written after name of element - Isotopes
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Differ in numbers of neutrons
Same atomic # - A greater value of n (shell number) denotes what?
- A greater electron energy and average distance from the nucleus
- First, second, third, and fourth quantum #'s?
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First/shell quantum # (n): size and energy of orbital
Second/subshell quantum # (l): shape (& energy) of orbital
Third/orbital quantum # (mL): orientation of orbital
Fourth/spin quantum # (mS): electron's intrinsic magnetism, spin of electron in orbital - Hund's Rule
- electrons in the same subshell occupy available orbitals singly, before pairing up
- Pauli Exclusion Principle
- no two electrons in the same atom can have the same set of four quantum #'s
- Can use periodic table to assign electron configurations, BUT beware of the d block whose n is in the d block because...
- the element has its outermost electrons in the subshell 1 less from the period number
- Atoms that are at a more stable, lower-energy state when an inner orbital electron is transfered to the outermost orbital:
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Copper, silver, gold, wants half-filled d
Chromium, molybdenum wants filled d - To find electron configuration of ions:
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For cations: losing 1 or more electrons--move to the left the # of squares equal to the # electrons lost to find the atom w/same config as the ion
For anions: gained electrons, move to the right by # squares equal to number of electrons added in order to find the atom with the same configuration as the ion - For transition metals: valence electrons from which subshell get ionized first?
- s, and only once these are gone do the d ones get ionized as well
- Ionization
- Process in which an ion is created from a neutral atom or molecule by adding or removing one or more electrons
- DIAMAGNETIC
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All electrons are spin-paired
-diagmagnetic
-repelled from a magnetic field - PARAMAGNETIC
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Not all electrons spin-paired
-attracted into a magnetic field - An electron is in its excited state when...
- it absorbs energy (em radiation or photon) equal to the difference in energy between level its in and current level
- What is always the amount of energy absorbed or emitted by an electron in moving between energy levels?
- = to the difference in the energy levels involved in the transition
- Fluorescence
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A process in which a compound emits light at one wavelength while being excited by radiation with a shorter wavelength
-observed when photons corresponding to lower-energy transitions are in the visible spectrum - What is an excited atom? Is it an ion?
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an excited atom is NOT an ion, because electrons are not lost or gained
-in an excited atom, electrons jump to higher energy levels within the atom - Absorption Spectrum
- -an energetic fingerprint of the element, gives a unique sequence of DARK lines that correspond to the specific frequencies and wavelengths at which atoms of the element can ABSORB photons
- What is a strong nuclear force?
- -stronger than electrical force between charged particles, because the strong nuclear force must overcome the electrical repulsion between the protons
- Characteristics of STABLE nuclei
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-# neutrons is usually equal to or slightly greater than # protons
-as atomic # increases, ratio of # of neutrons to protons increases - Radioactivity
- -characteristic of unstable nuclei, which undergo radioactive decay to make themselves more stable (altering # & ratio of protons & neutrons or just lowering their energy)
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The nucleus that undergoes decay is called the ____
The resulting, more stable nucleus is known as the ________ -
The nucleus that undergoes decay is called the _parent___
The resulting, more stable nucleus is known as the ___daughter_____ - 3 Types of Radioactive Decay
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Alpha
Beta
Gamma - What is alpha decay?
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-occurs when a large nucleus wants to become more stable by reducing # of protons & neutrons
alpha= 2 protons and 2 neutrons (same as a Helium nucleus)
-reduces the parent's atomic # by 2 and mass # by 4
MAIN POINT: decreases the number of neutrons and protons in large nucleus, subtracts 4 from mass # and 2 from atomic # - What is beta decay?
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3 types: B- (beta), B+, & Electron Capture
-the transmutation of a neutron into a proton or vice versa through the action of the WEAK NUCLEAR FORCE - E photon equation
- E photon= hf= (hc)/ lambda
- When the MCAT says "beta decay" without any further qualification, it means...
- B- decay
- What is B- decay?
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When an unstable nucleus contains too MANY neutrons, it may convert a neutron into a proton & an electron (a B- particle) is EJECTED
-mass # is same, atomic # of the daughter nucleus is 1 greater than the radioactive parent nucleus
MAIN POINT: decreases # neutrons, increases # protons, adds 1 to atomic # - What is B+ decay?
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-When an unstable nucleus contains too FEW neutrons, it converts a proton into a neutron & a positron, which is ejected
MAIN POINT: increases # neutrons, decreases # protons, subtracts 1 from atomic # - What is a positron?
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Emitted in B+ decay, it is the electron's antiparticle
-identical to electron BUT charge is +1
-atomic # of daughter is 1 less than parent, but mass # doesn't change - What is electron capture?
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-to increase its # of neutrons, an unstable nucleus captures an electron from the closest electron shell & uses it in the conversion of a proton into a neutron (show electron on right-hand side of equation)
-RESULT: atomic number reduced by 1, and mass # doesn't change (like in B+ decay)
MAIN PT: increases # neutrons, decreases # protons, subtracts 1 from atomic number - What is gamma decay?
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An expulsion of energy in the form of gamma photons (photons of em radiation)
-MAIN PT: brings an excited nucleus to a lower energy state, doesn't change identity of nucleus (neither mass nor atomic #)