Chem 1405 Test 3 Review
Viscosity
- a liquid's resistance to flow -thickness - inversely related to temperature -is affected by the size and shape of particles, and generally increases as the temperature decreases and as intermolar forces increase
Temperature of gas
- units in K (kelvin) - Kelvin = ⁰C + 273 - how fast the molecules are moving (speed) - zero Kelvin = gas stops moving / zero volume of gas
Pressure of gas
- units in atm ( atmospheres) or torr - 1 atm = 760 torr - the result of collisions of the particles with the container wall
Volume of gas
- units in ml, L - 1000 ml = 1L - the distance between the particles and the container wall
Moles
- units moles (n) - one mole = atomic weight in grams - # mole = # of grams of molar mass - the number of particles, the amount of gas
trigonal planar
-3 atoms bonded to the central atom - double-bonds -a molecule or ion with 3 regions of electron density around the central atom
tetrahedral
-Arrangement of four objects around a central atom. -Non-polar -single bonds
linear
-Arrangement of two objects around a central atom. -Non-polar. - double or triple bonds
Molecular
-Compounds formed from two or more different nonmetal elements -are brittle and do not conduct electricity -gases at room temperature = noble gases
hydrogen bonds
-H bonded to O, N, F ( H-O, H-N, H-F) -strongest bond -Strong dipole-dipole interaction between an H bonded to N, O, or F and a N, O, or F on another molecule -Water is an example of a compound that is able to hydrogen bond
Molecular Geometry
-Shape of molecule without lone pairs of electron - atom location - bent, linear, pyramid *If the central atom does not have dots, the electron geometry = molecular geometry
Octet Rule
-States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons - except for H and He -Boron is an element that often violates the octet rule
Polarity
-Tendency of a molecule, or compound, to be attracted or repelled by electrical charges because of an asymmetrical arrangement of atoms around the nucleus. -The greater the difference in electronegativity, the greater the polarity
Electron pair geometry
-The arrangement in 3D of the bonding electrons and lone pairs on the central atom of a molecule, set by the number of electron groups around that central atom. - linear, trigonal planar, tetrahedral -count how many regions surround the central atom: 2 regions (linear), 3 regions (trigonal planar), and 4 regions (tetrahedral) -the basic shape of a molecule, the result of the number of electron pairs that surround a central nucleus -determines whether a molecule is polar -does not distinguish between bonds and non-bonding pairs
Gas
-The phase in which matter has neither definite shape nor definite volume. -moves throughout the container - Is compressible - fluid (perfume or cologne) - low density -smaller elements and non-polar molecular compounds -example: steam, air in room *Gases obey the ideal gas law best when the pressure is low, volume is large and temperature is high
VSEPR Theory
-Valence-shell-electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible -bonds are pairs of shared electrons, and thus are negatively charged, charges repel one another - bonds will distribute themselves in three dimensions so as to maximize distance from one another
Lewis structure for polyatomic ions
-adjust the number of valence electrons -add one electron for each negative charge -example: CO₃²⁻ = 4 + (3x6) + 2 = 24
polar compounds
-asymmetrical (uneven) distribution of electrons, electrons are pulled toward one side of the molecule - have higher melting and boiling points, surface tension, and viscosity -mix best with other polar compounds -are sticky, looks unequal, lop-sided -central atom has non-bonding electron pairs -atoms bonded to the center have different electronegativity -dipole-dipole
dispersion force
-attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules -Exist in all substances -weakest of the forces, found in all molecules larger molecules have stronger dispersion force
Dipole-dipole force
-attractive intermolecular force resulting from the tendency of polar molecules to align themselves, such that the positive and negative ends are near each other -The attractions between oppositely charged regions of polar molecules -only polar molecules does this -strong attractions between molecules that have a permanent dipole moment
Lewis Structure
-diagram of the atoms and valence electrons in an atom, ion or molecule -valence electrons are illustrated as dots surrounding the atomic symbol -electrons that are shared are illustrated by lines connecting the atomic symbols
Metallic
-ductile, malleable, good conductors of heat and electricity, silvery luster, form cations by losing electrons -All elements to the left of the zigzag line except hydrogen -have high melting and boiling points -all except mercury are solids at room temperature and pressure -metals are not soluble in any common solvent except for other metals
Valence electrons
-electrons that are lost, gained, or shared during chemical changes -max. of 8 * Atoms are most stable if they lose all their valence electrons or gain enough to have 8 total -outer shell of electrons, most energy, this shell causes the exchange that creates molecules between atoms, chemical reactions happen because of this shell
Ionic compounds
-formed between metallic atoms that have extra electrons to spare, and non-metalic atoms which are electron deficient -have a metal or NH₄ -name of metal ion or NH₄ followed by name of negative ion - are hard, crystalline compounds with high melting and boiling points, they are electrolytes *all ionic compounds are solids at room temperature and pressure -(CATION then POLYATOMIC ION) such as potassium nitrate; or (CATION then ROMAN then POLYATOMIC ION) such as iron (II) hydroxide; or (POLYATOMIC ION then POLYATOMIC ION) such as ammonium nitrate
Solids
-has definite shape and volume - NOT compressible - Rigid - high density - metallic elements and very large molecular elements - ionic and large molecular compounds -example: aluminum at room temperature
Molecular compounds
-have 2 non-metals -Composed of two or more non metals. E.g. H₂O -are soft compounds with variable melting and boiling points, and are non-electrolytes -are composed of sets of atoms bonded together by pairs -molecular compounds can be classified into polar or non-polar
non-polar compounds
-have lower melting and boiling points, surface tension, and viscosity -they mix best with non-polar compounds -Symmetric - have all their valence electrons distributed symmetrically in space -Have an equal distribution of charges -must have only pure covalent bonds (electrons shared between atoms of equal electronegativity)
electronegativity
-indicates the relative ability of an element's atoms to attract electrons in a chemical bond. -increase from left to right on the periodic table, so covalent bonding often results between atoms on the same side of the table (similar attraction for electrons)
Liquid
-no definite shape, but has definite volume -Has a definite volume but takes the shape of their container -moves in relation to other particles - NOT compressible - fluid -medium density - only 2 elements: Hg and Br - medium sized and polar molecular compounds -example: water at room temperature
Pure covalent bond
-pair of electrons shared equally between 2 atoms with the same electronegativity - a pair of electrons is shared evenly between two atoms of equal electronegativity -almost always two atoms of the same element or C and H will be pure covalent bond
Acids
-substances that begin with H or end in acid -are molecular compounds that form ions in water (electrolytes)
Vapor pressure
-the amount of evaporated liquid that builds up in a closed container -the pressure exerted in a closed container by particles that have escaped the liquid's surface and entered the gaseous state -the pressure exerted by the molecules of a gas in the vapor state * vapor pressure is higher if imf is lower
Surface tension
-the force that pulls the surface of a liquid inward -a measure of the elastic force in a liquid's surface -best describes why spiders can walk-on water -the result of an inward pull among the molecules of a liquid that brings the molecules on the surface closer together
Intermolecular force
-the forces of attraction between molecules (positive and negative) -The attractive and repulsive forces among the particles in a sample of matter *the stronger the imf, the more likely that substance is to be a solid - also called van der Waal's forces
Normal boiling point
-the temperature at which a liquid turns into a gas at sea level -The boiling temperature of a substance at a pressure of 1 atm
Atomic element
-those elements that exist in nature w/ single atoms as their basic units -Argon is an example of an atomic element - atomic non-metal elements = noble gases=ideal gases- obey kinetic molecular theory
Lewis structure of molecules rules
1. Count the valence electrons for the entire molecule : PCl₃ = 5 + (3x7) = 21 2. Identify the central atom - the one with the lowest electronegativity : PCl₃ = P , SeO₂ = Se 3. Use lines to represent bonds : SeO₂ = O = Se - O 4. Fill in the rest of the electrons as dots until all atoms have 8 and or you have used all of the valence (Octet Rule) 5. If you run out of electrons before all atoms have an octet, use double or triple bonds *If there are metals on compounds, Lewis structure has no lines: X(metal)Y₃, BaCl₂ *Use lines only for non-metals
Kinetic Molecular Theory Assumptions
1. Gas is made of particles in constant motion 2. The volume of gas is the volume of the container which is mostly empty space 3. Kinetic energy is constant. They do not interact, they bounce, collisions are elastic 4. Kinetic energy depends on temperature. The hotter, the faster the speed. -Collisions are caused by gas molecules running into the walls of the container
Properties of liquids
1. normal boiling point 2. surface tension 3. viscosity 4. vapor pressure * normal boiling point, surface tension and viscosity are all higher if imf is higher * vapor pressure is higher if imf is lower
Covalent bond
A chemical bond that results from the sharing of valence electrons.
Single bond
A covalent bond in which one pair of electrons is shared by two adjacent atoms.
Triple bond
A covalent bond in which three pairs of electrons are shared by two adjacent atoms.
Double bond
A covalent bond in which two pairs of electrons are shared by two adjacent atoms.
Ideal gas law
PV=nRT R = 0.08206 L atm/mol K - use to find missing variable in a sample of gas that is not undergoing change
Combined gas law
P₁V₁/T₁ = P₂V₂/T₂ -use to find the amount of gas after a change occurs -if one of the variables does not change, it drops out of the equation
Molecular geometry
The actual shape of the molecule in the patter in 3D of the bonded atoms around the central atom of the molecule.
Gas Law variables
Volume (V) Pressure (P) Temperature (T) Moles (n) * ↑T = ↑P =↑V (like popcorn)
Polar covalent bond
pair of electrons NOT shared equally because one atom has higher electronegativity and pulls both electrons closer
Bonds
pairs of electrons shared between two atoms
