Chem Exam 2
Terms
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- molecule made up of 2 atoms
- diatomic
- chemical formulas that indicate the actual numbers and types of atoms in a molecule
- molecular formulas
- chemical formulas that give on the relative number of atoms of each type in a molecule
- empirical formulas
- sum of atomic weights of each substance in its formula
- formula weight
- mass of the collection of atoms represented by the chemical formula for a molecule
- molecular weight
- each of the atoms in the formula, represented by the chemical formula of the substance
- formula unit
- percentage by mass contributed by each element in a substance
- percentage composition
- (num of atoms of element)(atomic weight of element)/formula weight
- percentage composition
- amount of matter that contains as many objects as the number of atoms in exactly 12g of isotopically pure 12C
- Mole
- number of atoms in exactly 12g of isotopically pure 12C
- Avagadro's number
- mass of a substance in g/mol; always numerically equal to formula weight
- molar mass
- based on observation and experiment
- empirical
- angles made by the lines joining the nuclei of the atoms in the molecule
- bond angles
- AB2 bond angle
- 180 or bent
- AB3 bond angle
- 120
- AB3 name
- trigonal planar
- AB4 bond angle
- 109.5
- AB5 bond angle
- 3 are 120, 2 are 90
- AB6 bond angle
- 90
- AB4 name
- tetrahedral
- AB5 name
- trigonal bypyramidal
- AB6 name
- octahedral
- region in which electron will most likely be found
- electron domain
- best arrangement of a given number of electron domains??
- the one that minimizes the repulsions among them
- arrangement of electon domains about the central atomof an ABn molecule or ion
- electron domain geometry
- arrangement of only the atoms in a molecule or ion
- molecular geometry
- step 1 of VSEPR
- draw lewis structure and count total number of electron domains around central atom; each nonbonding pair, single, double, or triple bond counts as a domain
- step 2 of VSEPR
- determine electron domain geometry by arranging the electron domains about the central atom so that the repulsions among them are minimized
- step 3 of VSEPR
- use arrangement of bonded atoms to determine molecular geometry
- electron domains for nonbonding pairs exert_____ repulsive forces on adjacent electron domains, and thus tend to ______ bond angles
- greater, compress
- electron domains for ____ bonds exert a greater repulsive force on adjacent electrons than do electron domains for ____ bonds
- multiple; single
- run vertical, 90 to equatorial
- axial positions
- run horizontal
- equatorial positions
- domains for nonbonding pairs exert ______ repulsions than those from bonding pairs
- larger
- domains from nonbonding pairs always occupy these postions in a trigonal bypyramid
- equatorial
- measure of how equally the electrons in a bond are shared between the two atoms of the bond
- bond polarity
- as the difference in electronegativity between two atoms increases, so does the_____
- bond polarity
- quantitative measure of the amount of charge seperation in the molecule
- dipole moment
- the dipole moment depends on both the
- polarities of individual bonds and the geometry of the molecule
- the dipole moment that is due only to the two atoms in that bond
- bond dipole
- overall dipole moment of a polyatomic molecule is the
- vector of the sum of its bond dipoles
- if overall dipole moment is zero, then
- the bond is nonpolar
- provides a simple means for predicting the shapes of molecules
- VSEPR model
- model of chemical bonding in which an electron pair bond is formed between two atoms by the overlap of orbitals on the two atoms
- valence bond theory
- share the same region of space
- overlap
- orbital that results from the mixing of different kinds of atomic orbitals on the same atom
- hybrid orbital
- mixing of different types of atomic orbitals to produce set of quivalent hybrid orbitals
- hybridization
- covalent bond in which electron density is concentrated along the internuclear axis
- sigma bonds
- covalent bond in which electron density is concentrated above and below line joining the bonded atoms
- pi bond
- double bonds have this many sigma and pi, triple bonds have this many
- 1 sig 1 pi, 1 sig 2 pi
- sigma and pi electrons are associated totally with the two atoms that form the bond
- localized
- electrons are spread over a number of atoms in a molecule rather than localized between a pair of atoms; occur when there are resonance structures
- delocalized
- forces that exist between molecules
- intermolecular forces
- phase in which molecules are solid/liquid
- condensed phase
- solids that possess highly ordered structures
- crystalline
- the state of a substance depends largely on the:
- balance between the kinetic energies of the particles and the interparticle energies of attraction
- keep the particles apart and moving
- kinetic energies
- interparticle attractions tend to:
- draw the particles together
- intermolecular attractive forces that exist between neutral molecules
- van der waals forces
- exist between an ion and the partial charge on the end of a polar molecule
- ion-dipole force
- magnitude of ion-dipole attraction ______ as either the charge of the ion or the magnitude of the dipole moment increases
- increases
- neutral polar molecules attract wach other when the positive end of one molecule is near the negative end of another, overall affect is a net attraction
- dipole-dipole forces
- for molecules of approximately equal mass and size, the strenghts of intermolecular attractions ----- with increasing polarity
- increase
- boiling point ______as the dipole moment increases
- increases
- for molecules of comparable polarity, those with _______ molecular volumes generally experience higher dipole-dipole attractive forces
- smaller
- instantaneous force of dipoles, significant only when molecules are very close
- london dispersion forces
- esae with which the electron distribution in a molecule is distorted
- polarizablitity
- more polarizable molecules have ______ dispersion forces
- stronger
- strength of dispersion forces tends to ______ with increasing molecular weight
- increase
- liquid or solid in gas state
- vapors
- a force that moves something in a given direction; measure of the force exerted on a unit area, force/area
- pressure
- si unit of pressure
- pascal
- bar
- 10 to the fifth pascals
- inverted glass tube more than 760 mm long
- barometer
- Pressure sufficient to support a column of mercury
- standard atmospheric pressure, 760 mmHg
- the volume of a fixed quantity of gas maintained at constant temp is inversely proportional to the pressure
- boyle's law
- the volume of a fixed amount of gas maintained at constant pressure is directly proportional to its absolute temp
- charle's law
- at a given temp and pressure, the volumes of gases that react with one another are in the ratios of small whole numbers
- law of combining volumes
- equal volumes of gases at the same temp and pressure contain equal numbers of molecules
- avagadro's hypothesis
- volume of a gas maintained at a constant temp and pressure is directly proportional to the number of moles of the gas
- avagadro's law
- hypothetical gas whose pressure, volume, and temp behaviour is completely described by the ideal gas equation
- ideal gas
- standard temp and pressure
- 1 atm and 0 C
- volume occupied by one mole of ideal gas at STP
- molar volume
- the total pressure of a mixture of gases equals the sum of pressures that each would exert if it were present alone
- Dalton's Law of partial pressures
- pressure exerted by a particular component of a mixture of gases
- partial pressure
- Kinetic molecular theory, 5 key postulates
-
1. straight line motion, random direction
2.molecules are small (farther apart)
3. no intermolecular forces (cannot attract nor repel)
4. elastic collisions
5. mean kinetic energy is directly proportional to temp (in K) - speed of a molecule possessing average kinetic energy
- root mean square speed
- escape of gas molecules through a tiny hole into an evacuated space
- effusion
- spread of one substance throughout a space or throughout a second substance
- diffusion
- effusion rate of a gas is inversely proportional to square root of its molar mass
- graham's law
- distance travelled by a molecule between collisions
- mean free path
- deviations from ideal behavior _____ as temp decreases
- increase
- real molecues have:
- finite volumes and do attract one another