General Chemistry Midterm Review Notes PDF

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General Chemistry Midterm Review Notes...

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Molecular Shapes & Polarity: VSEPR (Valence Shell Electron Pair Repulsion Theory) - predicts molecular shapes! Steps for VSEPR 1 Draw Lewis Structure 2 Determine Central Atom 3 Count Number of Electron Domains 4 Arrange as to Minimize Repulsion 5 Consider Atoms to Determine Molecular Geometry

According to valence-shell electron-pair repulsion (VSEPR) theory, electron pairs around a central atom repel each other. This accounts for the geometries, or shapes, of molecules. Remember the difference between the shape of atom versus the electron arrangement. Lone electron pairs are ignored when describing the shape of the molecule. The molecular geometry of a molecule describes the three-dimensional shape of just the atoms. This is in contrast to the electronic geometry, which describes the shape of all electron regions . In order to determine the molecular geometry of a molecule, one must first determine the electronic geometry by drawing the Lewis structure.

Effect of lone pairs - lone pairs take up more space than bonding pairs. As a result, lone pairs push bonding pairs together and decrease the angle. Polarity - A polar molecule has polar bonds. However, polar bonds don’t guarantee a polar molecule. Ex:CO2 Valence Bond Model: Orbital overlap - requires room in orbitals, proper shape, proper orientation Orbital hybridization - adding or subtracting familiar atomic orbitals to come up with new, equally valid sets. Hybridization forms enough singly occupied orbitals on a central atom to make the bonds and handle all lone pairs. Note: The number of hybrid daughter orbitals is equal to the number of parent atomic orbitals. σ-bonding - bonding radially symmetric about bond axis Valence Bond Theory - what do electron clouds look like? Focus on individual electron bonds, predicts shapes of molecules, takes atomic orbitals into account. π Bonding - Double and triple bonding, isomerism, resonance, delocalized bonding

Molecular Orbital Model (MO): electrons spread over the whole molecule, not individual bonds. The shapes are different for every molecule and are therefore more complicated than valence bond theory and Lewis dot structures. It successfully accounts for or predicts certain chemical and physical properties more accurately than other bonding theories. The stability, bond length, bond order, and magnetism of a molecule can all be predicted. Metallic BondingBonding / antibonding orbitals - bonding orbitals push nuclei together, antibonding pull apart bond order - determined by subtracting the number of electrons found in orbitals by the number of electrons found in antibonding orbitals and then dividing that quantity by two. See below: bond order = (#e in bonding orbitals - #e in antibonding orbitals) / 2 resonance - for molecules with multiple Lewis Structures. All are equally valid and the true shape will behave like the average of all structures. More equivalent structure mean greater stability. semiconductors - Full valence band and short gap. HOMO & LUMO - Highest occupied molecular orbital/ Lowest Unoccupied molecular orbital Chemical Equations & Stoichiometry: Balancing Equations Guidelines: 1 Check formulas for reactants and products 2 Pick one element and attempt to balance 3 Repeat No. 2 for all elements 4 Divide out any common factors, simplest integer coefficients 5 Double-check all integers in equation Stoichiometry - ratio by which substances combine Conservation in Chemistry: mass, charge, total energy When a chemical reaction occurs, atoms rearrange to form new compounds, but no new atoms are created nor are any destroyed. Mass conservation can be seen in a balanced chemical equation, where the numbers of each kind of atom are the same on both sides of reaction arrow. mole and mass relationships - the coefficients in a balanced chemical equation provide the mole-to-mole stoichiometry among the reactants and products. The molar mass (in g/mol) can be used as the conversion factor between moles and the mass of a substance. Thus, the balanced equation and molar masses can be used in conjunction with one another to calculate the masses involved in a reaction.

Limiting Reactant, Yields: Actual yield - how much would be made in an actual reaction, usually less than theoretical yield Theoretical yield - how much would be made if everything available reacted % yield - a value equal to the actual yield divided by the theoretical yield times one hundred. %yield = (actual yield / theoretical yield) x 100 Limiting reactants - the one that runs out first during the reaction

Acids, Bases: strong & weak acids & bases - typically, the formula for an acid begins with H, although it can sometimes end in COOH. The easiest way to distinguish a strong acid from a weak acid is to memorize the seven strong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4, HBrO4) Any acid other than these seven must be a weak acid. The formula for a strong base contains the hydroxide ion, OH-. The formula for a weak base typically contains nitrogen, N. oxides - ionic and not technically salts neutralization acid-base reactions amphoteric substances - can act as either an acid or a base ex. H2O or HSO4conjugate acids & bases - a strong base has a strong tendency to be protonated in an aqueous solution; therefore its conjugate acid would have a low tendency to donate a proton. That means the relationship between the strength of a base and the strength of its conjugate acid is inverse: The stronger the base, the weaker its conjugate acid. If an acid is strong, it is completely dissociated in an aqueous solution, and its conjugate base has a negligible tendency to be protonated. According to the Brønsted-Lowry theory, an acid is any substance (molecule or ion) that can transfer a proton (H+ ion) to another substance, and a base is any substance that can accept a proton. Acid-base reactions are proton-transfer reactions, as follows: HA + B = BH+ + AChemical species whose formulas differ only by one proton are said to be conjugate acid-base pairs. Thus, A- is the conjugate base of the acid HA, and HAis the conjugate acid of the base

A-. Similarly, B is the conjugate base of the acid BH+, and BH+ s the conjugate acid of the base B. Strong acids have very weak conjugate bases, and very weak acids have strong conjugate bases. pH, Simple Titrations: Formulas: pH=-log[H+], [H+]=10^-pH pH scale simple acid-base titrations acid-base equilibrium autoionization of water titration: a procedure for determining the concentration of a solution by allowing it to react with another solution of known concentration (called a standard solution ) . Acid-base reactions and oxidation-reduction reactions are used in titrations. For example, to find the concentration of an HCl solution (an acid), a standard solution of NaOH (a base) is added to a measured volume of HCl from a calibrated tube called a buret . An indicator is also present and it will change color when all the acid has reacted. Using the concentration of the standard solution and the volume dispensed, we can calculate molarity of the HCl solution. The stage in a titration when the exact volume of solution needed to complete the reaction has been added is called the stoichiometric point  or equivalence point . To detect the equivalence point, a few drops of an acid-base indicator are added to the analyte before the titration....