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MCAT Chem Packet 1

Chemistry

QuestionAnswer
Avogadro's # 6.022X10^23
Mass # protons+neutrons
charge of electron 1.6x10^-19 Coulombs
atomic # Z # protons=#electrons unless it's charged
isotope #neutrons change so mass changes but atomic #same
electron - charge, closer to nucleus the lower energy level, less interaction w/environment
cation gain + charge, loose e-, decrease radius, move to left of periodic table for e- config
anion gain - charge, increase radius, move to right on periodic table for e- config
valence e- VE=atomic group #
Plancks quantum theory energy is emitted as electromagnetic radiation from matter exist as discrete bundles called quanta E=hf=hc/╗(wavelength) c=3.0X10^8m/s h=6.626x10^-34 J*s
Bohr Model Predicted changes in discrete amounts w/ respect to n L=nh/2π n=principal quantum # h=planck constant
Bohr Energy of electron E=-Rh/n^2=-Rh(1/n^2initial-1/n^2final) E=- absorption E=+ emission E↑ negativity↓ n↑ e- goes from lower level to higher they AHED: Absorb light, Higher potential, Excited, Distant from nucleus
Energy of photon emmitted E=hf=hc/wavelength
Lyman Series Group of H emission lines corresponding to transition from upper levels n>1 to n=1
Balmer Series From energy levels n>2 to n=2
Paschen Series From energy levels n>3 to n=3
Absorption energy bands when energy absorbed. see light emitted NOT absorbed
heisenberg Uncertainty Principle uncertainty of position of a particle and it's momentum. You can know position but not momentum and vice versa ▲x▲p≥h/2
Pauli Exclusion Principle No two e- in the same atom can have same four quantum #'s
Quantum Number Table #1 principle (n) (1,2,3..) shell (energy level, # of period # on periodic table) #2 azimuthal (l) (0,1..(n-1)) subshell: s L=0; p L=1; d L=2; f L=3 #3 magnetic (ml) (-L to L) orbital: px;py;pz #4 spin (ms) (-1/2, +1/2) spin (↑↓)
Quantum number equation # of total orbitals= n^2 # of e- within shell= 2n^2 # of e- within subshell= 4L +2
Aufbau Principle each new proton added creates new element and each new e- occupies lowest energy level (n) BOWLOW stability ↑ fill lowest n level with n+l if same pick lowest n
Electron configuration 1) List shells &subshells of element e- from lowest to highest 2) Add subscript after each subshell to indicate # of e- Ex: Fe: 1s2 2s23s23p64s23d6 or [Ar]4s23d6 Exception: Half & completely filled subshell preferred
Electron Config Exception Exception: Half & completely filled subshell preferred Ex: Cr: [Ar]4s23d4→[Ar]4s3d5 Anion: move toward RIGHT of element Cation: move toward LEFT of element Ex: [Br-]: [Ar]4s2 3d10 4p6
Hund's Rule e- will NOT fill any orbital in the same subshell until all orbitals have at least 1 e- ie: Fill them single than paired (↑↓)
Paramagnetic elements with unpaired e- Ex: Li 1s:↑↓ 2s:↑ & PARALLEL when external field applied
Diamagnetic elements with NO unpaired e- & UNAFFECTED Be: 1s:↑↓ 2s:↑↓
Periodic table trends Across Periodic Table: ↑ Ionization Energy, Bond Order, Electron Affiinity, Zeff, Electronegativity ↓Atomic radius Down Periodic Table: ↓Ionization Energy, Bond Order, Electron Affiinity, Electronegativity ↑Atomic radius, Zeff
Chemical properties of Periodic Table Metals: Loose hold on outer e-, form cation, thermal &electrical conductive Metalloids: Metal &nonmetal characteristics Nonmetals: Form covalent bonds w/on another, form anion, ↓ melting pt
Atomic Radius Distance from center of nucleus to valence e- ↑radius↓down periodic table→across table (R to L) due to protons weaker pull to e-
Electrostatic force Force b/w charged objects (F=kQ1Q2/r^2); attractive b/w opp charges & repulsive b/w like
Effective Nuclear Charge (Zeff) Amount of charge felt by most recently added e- ↑Zeff←(L to R) ↓Top to bottom ↓shielding
Ionization energy Energy required to detach an e- from atom ↑IE→(L to R)↑Bottom to top Why? e- are closer to nucleus
First vs Second IE First IE: Energy required to detach 1 e- from neutral atom to form (+1) cation Second IE: Energy required to detach 2 e- from neutral atom to form (+2) cation Second IE>First IE b/c second IE more stable
Electronegativity Tendency of atom to attract e- shared in covalent bond The LARGER the diff b/w electronegativities the LARGER the polarity so ↑attraction
Electron Affinity willingness of an atom to accept addition of e- E RELEASED when e- added ↑EAffinity→(L to R)↑Bottom to top table ▲H is (-) & EXOTHERMIC to the right &up periodic table ▲H is (+) & ENDOTHERMIC for noble gases
octet rule atom will bend until it has full outermost shell similar to noble gases Exceptions: some have less than 8e-;in or beyond 3rd period can have more than 8e- so more than 4 bonds
Lewis Structure Rules 1) Find total # of valence e- for all atoms 2)Use pair of e- to form single bonds 3) arrange remaining e- into lone pairs &double or triple bond to satisfy duet/octet rule Total # e-=Σvalence e-
Formal charge VE-(Nnonbonding (dots)+ 1/2Nbonding (sticks))
Bond ranking Ionic>covalent>hydrogen bonding>dipole-dipole>van der waals
Ionic bonding -covalent bond where valence e- are transferred to one atom (unequal sharing) creating polarity -most enegative atom attracts e- -b/w metal &nonmetal -High melting pt -soluble in H2O & insoluble in nonpolar conducts electricity in aqueous soln
Covalent bonding -valence e- are shared equally -similar enegativities -soluble in nonpolar -insoluble in H2O -low melting pt and boiling pt -nonconductor of heat & electricity
Dipole Moment occur when (+) charge center is not same as (-) charge so e- are pulled to one side
Polarity -determined by geometry of molecule (due to dipole orientation)
Intermolecular attraction Types attraction b/w molecules due to dipole moment 1)London Forces (van der waals) 2) Hydrogen Bond 3) Dipole-dipole 4)Induced dipole 5) Instantaneous dipole moment
London Forces weakest interactions b/w two instantaneous dipoles ↑size of atom/structure↑dispersion forces
Hydrogen bond bond b/w H, N,O,F involved in intra(b/w molecule) & inter(b/w 2 compounds) interactions
Dipole-Dipole occurs b/w oppositely charged ends of polar molecules; stronger than London evident in interactions in solid &liquid phase but negligible in gases
Induced Dipole occurs when dipole moment is created in NON-POLAR molecule or bonded to a polar, ion molecule or electric field -weaker than permanent dipoles
Instantaneous Dipole Moment arise spontaneously in non-polar molecule Why? -e- move around & become uneven create dipole in neighboring atoms
Bond Length distance b/w two nuclei of atoms involved in bond ↑Shared e-↓Bond length
Bond Energy (Bond Dissociation Energy energy required to break bond and separate components to gaseous state ↑Bond E↑Bond Strength↓Bond length
Realtionship b/w bond length, strength, &energy Bond Length: single bond >double bond>triple bond Bond Strength: single<double<triple Bond Energy: single<double<triple
Hybridization sigma bond: bounding pair of e- found in space b/w bonding atoms Lowest Energy; Strongest Most Stable pi bond: overlapping p orbitals, More Reactive ↑s character↓bond length↑bond strength↑bond energy↑stability sp (50:50)>sp2(33:66)>sp3(25:75)
Aromaticity &Huckel Rule 4n+2π=# of e- ↑e- delocalization ↑stability
Resonance Structure Molecule is an average of all resonance structure w/lowest energy & greatest stability ↓separation of charge ↑stability ↓formal charge on most atoms ↑stability conjugate base of an acid exhibits resonance ↑stability so weaker base & stronger acid
Fisher Projection OH H ╪ H H H CH3 Horizontal lines(---): out of scope vertical lines(: into page
Newman Projection Anti: Θ=180 Gauche: Θ=60 Eclipsed Θ=120 Fully Eclipsed Θ=0
Valence Shell Electron Pair Repulsion(VSEPR) Geometry Linear (sp) & Trigonal planar (sp2) [# of bonds=2] [#lone pairs=0] linear AX2 [#of bonds=3] [#lone pairs=0] trigonalplanar AX3 [#of bonds=2] [#lone pairs=1] bent AX2E1
Valence Shell Electron Pair Repulsion(VSEPR) Geometry Tetrahedral (sp3) [#bonds=4][#lone pairs=0] tetrahedral AX4 [#bonds=3][#lone pairs=1] trigonal pyramidal AX3E1 [#bonds=2][#lone pairs=2] bent AX2E2
Valence Shell Electron Pair Repulsion(VSEPR) Geometry Trigonal bipyramidal (sp3d) [#bonds=5][#lone pairs=0] trigonal bipyramidal AX5E0 [#bonds=4][#lone pairs=1] seesaw AX4E1 [#bonds=3][#lone pairs=2] T-shape AX3E2 [#bonds=2][#lone pairs=3] linear AX2E3
Valence Shell Electron Pair Repulsion(VSEPR) Geometry Octahedral (sp3d2) [#bonds=6][#lone pairs=0] octahedral AX6E0 [#bonds=5][#lone pairs=1] square pyramidal AX5E1 [#bonds=4][#lone pairs=2] square planar AX4E2 [#bonds=3][#lone pairs=3] Tshaped AX3E3 [#bonds=2][#lone pairs=4] linear AX2E4
Created by: aperez48