Chemistr Lecture
– Atoms, Molecules and Quantum Mechanics
Examkrackers MCAT Co prehensive C urse, Charles F eng http://fenguin.net/mcat —
[email protected] — (224) 5 32-0039
Atoms Nucleus (pr tons, neutrons) + electrons Elements w itten as = pr tons + neutrons o = mass number = = atomic number = = protrons o o = element symbol (i.e. Mg) Isotopes: Isotopes: sa e atomic nu ber (same # rotons), diff ass number ( diff # neutron s) Atomic weight/molar mass: from periodi table, defined in amu or g mol (when d we use?) # moles # grams / m lecular weight o Ion: Ion: diff # el ctrons than protons, so has a charge (+ c tion, - anion) Size differences: For same element: cations are smalle r than neutral, anions are la rger than neu tral o For same # electrons: smaller with hi her atomic number b/c of more attractiv e force from rotons o
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P riodic Table Period : horizontal row Group/Fami y : vertical col mn, numbered 1-18 or IA-V IIIA, IIIB-IIB Types of elements Metals: Metals: o Tend to lose electr ns to form po sitive ions Ductile, malleable, hermal/electrically conductive, luster (shi ny) Gene ally solids @ r oom tempera ure except mercury Usually form ionic xides Transitio metals: metals: in th sunken area of the periodic table (sectio n B groups) o Nonmetals: ls: tend to gai n electrons to form negativ ions, usually form covalen oxides o Metalloi s: between a etal and a n nmetal o Groups/Families tals (Group 1 ): low melting point, form 1+ cations, reac t strongly wit most nonm tals including water (to o Alkali metals (Group form hydroxides and hydrogen gas) metals ( roup 2A): hig er melting p int, less reactiive than 1A, f rm 2+ cations o Alkaline arth metals ( Group 4 : can form fo r covalent bonds with non etals. C can f orm strong pi bonds, every hing else can form two o addition l bonds for a otal of 6 Group 5 : can form th ee covalent bonds. N can f rm strong pi onds, everyt ing else can f orm two addi ional o bonds for a total of 5 Chalcogens (Group ns (Group 6A): oxygen and ulfur most important, both can make str ng pi bonds. Oxygen reacts with o metals t form metal o xides. Pure sulfur is S8 Halogens (Group 7A): F, Cl, Br, I. All ex ist as diatomic molecules a d like to gain electrons o Noble ga es (Group es (Group 8A): nonreactive, normally fou d in nature a isolated ato s o Diatomic m lecules: lecules: H, O, , Cl, Br, I, F Small atoms can form pi form pi bonds, onds, large at ms (3rd perio or above) ha ve d orbitals s o can form m re than 4 bon ds
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Chemistr Lecture
– Atoms, Molecules and Quantum Mechanics
Examkrackers MCAT Co prehensive C urse, Charles Feng http://fenguin.net/mcat —
[email protected] — (224) 5 32-0039
P riodic Trends Ionization e ergy : energy it takes to rem ove an electron Electronegat ivity : tendenc to attract an electron in a ond Electron affi ity : willingne s of an atom t o accept an a ditional elec ron Start with E: (energy of io ization, electron affinity, el ctronegativit ) increase goiing LEFT-RIGH T, BOTTOM-T P Don’t start ith E: (atomic radius, metallic character) i crease going RIGHT-LEFT, OP-BOTTOM • • • • •
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Units: kg, m, s, A, K, cd, mol Prefixes: me a/kilo/deci/c nti/milli/micro/nano/pico/ emto olecules: separate and distinct units made of atoms Empirical for mula: relative number of at ms of one el ment to anot her Molecular formula: exact number of ato s per molecule Calculating ercent composition by ma s o For each atom, find weight of atom i molecule / total molecula weight Calculating mpirical for ula from percent mass o Assume 100 gram sa ple, multiply by % masses to find # gra s of each ele ent o Find # moles of each el ement from t e # grams Divide b smallest # of moles to get mpirical formula (might ha ve to multiply by a factor to make all num bers o integers) If we wa t the molecul ar formula, have to use (giv n) total mole cular weight o
B nds Covalent bo d : shares electrons; electro s closer to m re electrone ative atom Bond dissoci tion energy/bond energy : e ergy it takes o break a bon d o Higher bond energy = lower bond length o Double onds have hi her bond en rgy (lower length), triple bo nds even hig er/lower Compound : ubstance made from two o r more eleme ts • •
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Naming comp unds Ionic : cation + anion o Cations sually just na e of elemen o Metals with more than one possible harge (i.e. copper) called c pper (I) or co pper (II) o Anions of elements en in -ide Polyato ic anions containing oxygen end in -ite or -ate (also hy o- -ite and p r- -ate) o Acids: name after anion o Acids of lements = hydro- element ic o Oxyacds = anion name -ic/-ous acid Binary mole ular compounds (2 element ): leftmost/lo est, then oth er one w/ prefixes •
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Chemistr Lecture – Atoms, Molecules and Quantum Mechanics Examkrackers MCAT Co prehensive C urse, Charles Feng http://fenguin.net/mcat —
[email protected] — (224) 5 32-0039
Chemical reac ions Physical vs c emical changes: chemical hen molecular structure is hanged Remember o balance all quations! Limiting reagent: what will get used up irst o Find # moles available of each reactant o Look at ratios between coeffs in balanced equatio to find out hat gets used up first Theoretical s actual yield o Theoreti al is what’s p edicted by equation, actual is what you g et in an exper iment • • •
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Percent y ield : % yield
⋅ 100%
Types of Re ctions o Combination: A + B Decomp sition: C A + B o Single dis placement : A BC B + A o Double d isplacement : B + CD AD + CB o
Quantum Mec anics Quantum n mbers Principal quantum number : shell le el o o Azimuth l quantum nu mber : subsh ll/orbital sha e: s, p, d, f. Ca n range from 0 to 1 Magnetic quantum nu ber : whic orbital; rang s from to o Electron pin quantum umber : /2 or 1/2 o Pauli exclusi n principle: n two electron s can have th same set of uantum num bers Hund’s rule: ne electron ill go into ea h available orbital before a y orbital has 2 electrons Aufbau prin iple: electrons look for an a ailable orbital with the low st energy sta e 1s 2s 2p 3s 3 4s 3d 4p 5s d 5p 6s 4f 5d 6p … Electron con iguration: Br = 1s22s22p63s23p64s 3d104p5 = [Ar] 4s23d104p5 o Exceptio s: 4s23d4 s13d5, 4s23d9 4s13d10 o For ions, make sure yo have the rig t number of lectrons o Heisenberg ncertainty pri ciple: we can never be sure about both t e position and the momen um of a parti le ΔΔ 2 •
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Electromagne ic Energy Planck’s quantum theory : electromagnetic energy is q antized in dis crete increments For a photo , and / Emission sp ctra: Electron have specific quantized energy levels th t are unique f or each atom o When a hoton of the right wavelen th hits the at om, it can exc ite an electro to a higher energy level o After a while, the elect on drops fro the high en rgy level rele sing another photon o If you us a wide spectrum of light, y ou can see w at wavelengt h of photons re released t identify the o Photoelectric effect: Electron can be eject d from metal by shining lig t on it o o The light energy must be greater than the work fu ction Φ of th e metal o The kine ic energy of e ected electron Φ • • •
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