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Chem 105 Midterm 2
| Term | Definition |
|---|---|
| chemical bond | electrostatic attraction holding two atoms close together (not sticks, 2 nuclei attracted to the electrons between them) |
| lower energy state = | more stable two H atoms sharing electrons is more stable than two separate H |
| ionic bonds | complete transfer of one of more electrons from one atom to another (attraction of ions) |
| covalent bonds | valence electrons are shared equally between atoms |
| however, most bonds are __ _______ ionic and covalent bonds | in between |
| electronegativity (EN) | ability of atom to pull electrons in a tight bond towards itself |
| EN has same periodic trend as | electron affinity (EA) and IE (ionization energy) so as you go left to right, it goes up (generally) and as you go from the bottom to the top it also goes up |
| delta X | difference in EN values predicts whether those atoms will share electrons or if one atom will hog electrons |
| delta X < 2 | covalent |
| delta X > 2 | ionic |
| metallic bond | metal atoms sharing a sea of electrons |
| ionic bonds are ____ + _____ or _____ + ______ | cation + anion metal + nonmetal |
| crystal lattice | ordered 3D array of particles |
| lattice energy is proportional to | energy required to break apart the lattice (separate the ions) a measure of how deep the energy well is |
| trend in lattice energy going down a group | decreases due to larger ionic radius |
| 0 < X < 0.4 | nonpolar covalent bond (equal sharing) |
| 0.4 < X < 2 | polar covalent bond (unequal sharing) |
| bond dipole | separation of electrical charge created when atom of different EN forms covalent bond with another atom |
| dipole moment | quantifies the extent of charge separation measure degree to which molecule aligns in an applied electrical field written from + to - (arrow) |
| polar molecule | has a net dipole moment asymmetric distribution of charge more negative charge exists over some part of the molecule than another part |
| H2O CO2 | polar (because it is bent, so arrows are not perfectly symmetrical) CO2 nonpolar (symmetrical, balances charges) |
| symmetric stretch | infrared inactive dipole moment arrows are both going in towards each other or both going out away from each other |
| asymmetric stretch | infrared active both dipole arrows are going the same way to the same side |
| bending mode | infrared active pulls end molecules up or down, creating a bent or V shape |
| binary molecular compounds | 2 main group nonmentals prefix + element name + prefix + base name + "ide" |
| P4S9 | tetraphosphorus nonasulfide |
| SO3 | sulfur trioxide (don't use mono for first one) |
| one | mono |
| two | di |
| three | tri |
| four | tetra |
| five | penta |
| six | hexa |
| seven | hepta |
| eight | octa |
| nine | nona |
| ten | deca |
| main group metals | just name the metal if its an ion, say the name of the metal and then ion |
| Mg 2+ | magnesium ion |
| transition metals | can form multiple cations, so charge is included in roman numerals |
| Fe 2+ Fe 3+ | iron (II) ion iron (III) ion |
| Zn | zinc is always 2+ so may or may not be written |
| monoatomic anions | end with ide |
| O 2- | oxide |
| F- | fluoride |
| metal cations + nonmetal anions | Na + and Cl- --> NaCl sodium chloride 2 Fe 3+ and 3O 2- --> iron (III) oxide |
| some salts can be hydrated meaning that | water molecules sits inside crystal lattice |
| CuSO4 * 5H2O | copper (II) sulfate pentahydrate |
| hydrated salts | name ionic salt add "prefix" hydrate |
| hygroscopic salts | absorb water from the air |
| desiccants | in diapers absorbs water |
| binary acids | H+ with a halogen anion "hydro" + halogen base name + "ic" and then the word acid |
| HBr | hydrobromic acid |
| oxacids | H+ with a oxygen-containing polyatomic anion |
| if oxoanion ends in "ite" | -ous |
| if oxoanion ends in "ate" | -ic |
| covalent compounds | share electrons to form an octet |
| ionic compounds | lose or gain electrons to form an octet |
| bonding pairs vs electrons | electrons shared in a bond electrons not shared |
| bond order | number of bonds between a pair of atoms |
| bond length | higher bond order = shorter length (more electron density between atoms, pulling the nuclei closer) triple bonds are shorter than double bonds which are shorter than single bonds |
| bond strength | higher bond order = stronger bond (takes more energy to break) triple bonds have more bond strength than double and single bonds |
| smaller atoms generally have | a shorter length and a stronger bond |
| bond energy | energy needed to break 1 mole of covalent bonds in the gas phase |
| bond strength is inversely proportional to | bond length |
| resonance structures | more than one arrangement of lewis structures |
| delocalization | spread of electrons over more than one bond |
| bond order of delocalized (resonance) bonds: | number of bonds/possible bonding positions (number of bonding pairs of electrons/number of bonding positions) |
| formal charge (FC) = | VE - (number of electrons in lone pairs - number of bonds) |
| the best Lewis structure | minimizes formal charge puts negative charge on most electronegative atom |
| atoms in period __ and below can expand their octet | 3 (except Mg, Na) |
| when do they expand their octet? | when it decreases formal charge on central atom, when there ar e more than enough electrons to go around when you need to complete the amount of electrons |
| period 3 elements and below period 2 elements and above 9 (Z<12) | minimize formal charge minimize formal charge while following octet rule |
| free radical | odd-electron molecule with an unpaired electron in its Lewis Structure usually very reactive - because it wants to pair that electron |
| less than an octet/depleted octet | Be, B, Mg can occur when it minimizes formal charge |
| elements | N, N2 pure elements |
| molecules | N2, HCl any two atoms together, whether they're the same or different |
| compounds | HCl two different atoms together |
| law of definite proportions | a given chemical compound always contains its constituent elements in the same mass proportions, regardless of its source applied to one compound ex: water is always 89% oxygen no matter where it came from |
| law of multiple proportions | two elements form multiple compounds, the ratio of the masses of the second element that combine with a fixed mass of the first element will be a ratio of small whole numbers applies to two or more compounds ex: carbon and oxygen can make CO or CO2 |
| 3d __ __ __ __ __ | that is the subshell ____ - one of these is the orbital |
| He --> H | ionization energy is huge, hard to break up s shell cause its very strong and close to the nucleus |
| we ____ map an exact path of an electron | cannot! based on probability |
| electron diffraction proves that | electrons behave like waves |
| polar molecule | molecule with a net dipole moment (asymmetrical distribution of charge) more electron density exists in some parts of the molecule vs others |
| how to tell if a molecule is polar | has at least one polar bond that doesn't cancel out has lone pairs/polar bonds distributed asymmetrically |
| VSPER models | best arrangement of electrons is one that minimizes repulsion (keep electrons as far apart as possible) |
| steric number (SN) | number of things around an atom (lone pairs and bonds) |
| electron geometry SN=2 | linear 180 |
| electron geometry SN=3 | trigonal planar 120 |
| electron geometry SN=4 | tetrahedral 109.5 |
| electron geometry SN=5 | trigonal bipyramidal 90, 120 between equatorials |
| electron geometry SN=6 | octahedral 90 |
| molecular geometry SN=3, trigonal planar | 1 lone pair - bent (degree is now less than 120, about 117) |
| molecular geometry SN=4, tetrahedral | 1 lone pair - trigonal pyramidal (degree now less, 107) 2 lone pairs - bent (degree now less, 104) |
| molecular geometry SN=5, trigonal bipyramidal | 1 lone pair - seesaw/sawhorse 2 lone pairs - T-shaped 3 lone pairs - linear |
| molecular geometry SN=6, trigonal planar | 1 lone pair - square pyramidal 2 lone pairs - square planar 3 lone pairs - T shaped 4 lone pairs - linear |
| why do the degrees get smaller as you add in lone pairs? | because lone pairs take up a lot of room, pushing the atoms down to have a lower angle |
| equatorial vs axial lone pairs | equatorial - ones of the side axial - ones vertically up and down |
| less electron repulsion at the top so put electrons in the _____ positions | equatorial |
| isomers | same chemical formula, different 3D structure |
| constitutional isomers | different connectivity of atoms (keeps same formula) different compounds --> different chemical and physical properties |
| stereoisomers | connected in same order but with different spatial arrangement |
| enatiomers | "chiral": nonsumperimosable mirror image (mirror image is not identical) |
| diasteromers | can either be conformers or cis/trans isomers |
| cis/trans | cis: two of the same atoms on the top, two of the same atoms on the bottom trans: top and bottom of double bond are different pairs of atoms double and triple bonds can't rotate |
| conformers | rotation around single bonds |
| organic chemistry | study of carbon containing compounds |
| functional group | a common structural subunit |
| ends/kinks are ___ where as __ are implied | ends and kinks are carbons, and hydrogens are implied (only off the carbon) |
| hydrocarbons: alkanes | C-C single bonds saturated hydrocarbon |
| hydrocarbons: alkenes | one or more double C=C bonds unsaturated hydrocarbon |
| hydrocarbons alkynes | one or more triple CC bonds unsaturated hydrocarbon |
| saturated hydrocarbons (alkanes) | have max amount of H per C in the chain singles bonds stacks easy - SOLID high melting point |
| unsaturated hydrocarbons | have less than max H per C, because the double or triple bonds can break and bind with more H in a process called hydrogenation |
| hydrogenation | combining with more H to make an alkane |
| trans-unsaturated fats | H atoms are opposite of the double bond easy to stack, SOLID/SEMI-SOLID high ish melting point |
| cis-unsaturated fats | H atoms on same side of double bond, causing it to be raised and bent kinked, stacks less well, LIQUID lower melting point |
| saturated fats | no kinks, stack better, density higher butter |
| how to tell if molecule is chiral? | if the molecule contains stereocenters --> a carbon bonded to 4 different atoms or groups |
| sigma bonds | head to head overlap single bonds ex: ss, sp, sp^2 |
| hybrid orbitals | you can mix orbitals of an atom to form a new set of valence orbitals (to accommodate splitting the electrons) |
| total number of orbitals must be | conserved |
| SN=2 | sp 4 blue, 2 purple |
| SN=3 | sp^2 2 blue, 3 purple |
| SN=4 | sp^3 4 purple |
| SN= 5 | sp^2d 5 purple |
| SN=6 | sp^2d^2 6 purple |
| pi bonds | side to side double/triple bonds |
| ex: C=C bond | 1 sigma bond + 1 pi bond (so a triple carbon bond would be 1 sigma bond and 2 pi bonds) |
| rotation is restricted around the C=C bond because | doing so would break the pi bond, a process requiring a ton of energy |
| sigma overlap is _____ that pi overlap, resulting in a _____ bond | greater stronger bond |
| anti-bond | higher energy, decreased electron density between the nuclei |
| bonding | lower energy, increased electron density between nuclei |
| rules for MOs | fill from bottom to top, fill lowest ones first (aufbau) 2 electrons per orbital (Pauli) fill degenerate orbitals singly before pairing (Hund's) |
| HOMO | highest occupied (with at least one electron) molecular orbital |
| LUMO | lowest unoccupied molecular orbital |
| an electron can jump from HOMO to LUMO by _____ a photon | absorbing |
| and it can ____ a photon by relaxing to a lower MO | emit |
| bond order in MOs | (bonding electrons - anti bonding electrons)/2 |
| pi bonding have nodes | along internuclear axis |
| anti bonds have nodes | between atoms, (horizontal), perpendicular to internuclear axis |
| Lewis Structures VESPR Theory VB Theory MO Theory | connectivity between atoms, lone pairs + bonds 3D geometry, minimizes electron repulsion hybridizes orbitals\ whole new set of orbitals, shows magnetism |
| amino acids | carboxylic acid linked with amine end forms a peptide bond or amide bond or polypeptide |
| conduction band | unoccupied (or partially filled) orbitals typically higher in energy |
| valence bond | bond of orbitals filled (or partially filled) by valence electrons |
| electrons can change from CB to VS quickly if the bands are | close together, or even better when they overlap |
| HOMO - _____ band LUMO - ______ band | HOMO - valence band LUMO - conduction band |
| metal - CONDUCTORS | overlap of CB and VB electrons change orbitals easily |
| semiconductors | small energy gap between VB and CB |
| insulators | large energy gap electrons do not delocalize easily, don't conduct |
| doping | replacing a small amount of atoms to increase or decrease conductivity |
| n-type | when a semiconductor (like Si) is doped with an anion/electrons - NEGATIVE donor level goes UP towards conduction band |
| p-type | when a semiconductor (Si) is doped with a cation/less electrons - POSITIVE acceptor level is DOWN near the valence bond |
| n- type is a semimetal with an electron ____ dopant | rich |
| p-type is a semimetal with an electron ____ dopant | poor |
| any double bonds in a ring ______ be cis/trans isomers | cannot |
| to find a stereoisomer go | as far as you can out to find a difference |
| constitutional isomers are also called ______ isomers and _______ isomers and they all mean the same thing | positional, chain |
| anything larger than propane | has constitutional isomers and conformers |
| methane | one carbon |
| ethane | 2 carbons |
| propane | 3 carbons ^ |
| butane | 4 carbons |
| pentane, hexane, heptane, octane | 5, 6, 7, 8 carbons |
Created by:
anyasalmon