exam #4: study guide (binary compounds, kinetic molecular theory, gas laws)

%%chemical formulas & naming compounds:%%

the basics:

- when we have been showing substances, we have been using chemical formulas, which show qualitative and quantitative information about the substance

- the %%chemical symbols%% = elements present

- the %%subscripts%% = how many atoms of each element

types of formulas:

%%empirical formula%% - the simplest ratio in which atoms combine to form a compound

ex.: KCl, CaO, Al2O3, CH2O

%%molecular formula%% - the formula that tells you what is part of a molecule (the smallest unit of a covalent compound)

ex.: H2O, C6H12O6

this does NOT have to be the simplest ratio of elements

oxidation states/oxidation #:

%%an atom’s oxidation state%% = its hypothetical charge if you assume all its bonds were fully ionic

ex.: Na has an oxidation state of +1; you can interpret this as Na forms an ion with a 1+ charge in an ionic bond

unless otherwise shown, you should use the top number, which is the most common oxidation state!

naming compounds (pt. 1):

%%binary ionic compounds%% (2 parts)

- rules for writing formulas: elements with positive oxidation #’s combine with elements with negative oxidation #’s (USE THE TOP # FOR NOW)

- the algebraic sum of all the charges that you have must be zero to reach a compound that is overall neutral

- write the formula starting with the element with the positive oxidation #, then the one with the negative # number

%%“cross & drop”%%

  1. write the elements and their oxidation states above the respective elements in the appropriate order (positive, then negative)
  2. take the number of the oxidation state (not the charge!) of one element and write it as the subscript of the other for both elements
  3. %%scale%% the numbers down to the simplest whole number ratio possible

%%giving compounds names%%

for binary ionic compounds, we do the following

  1. %%keep%% the first element (the positive one) as is
  2. %%use the suffix “–ide”%% instead of the normal name of the second element

- %%ending in -ine, -ium or -on%%: swap the suffix out for “i-de” directly (“carbide,” “chloride,” “telluride”)

- %%ending in –gen%%: drop the vowel preceding the suffix as well before you swap for “-ide” — ”hydride” “oxide”

weird ones: sulfur = “sulfide,” phosphorus = “phosphide,” antimony = “antimonide,” arsenic = “arsenide”

“what happens if your metals have multiple oxidation states?”

the stock system! - used to indicate specific oxidation states for %%metals%% that have multiple oxidation states

- positively charged elements only

- for elements that have %%multiple oxidation states%%, a roman numeral in parentheses is added to the name to show the one it has in the compound being shown

ex.: FeCl3—iron (III) chloride

remember—all compounds should end up with 0 charge, so use the charge of the other element to help you figure out what you have!

compounds with polyatomic ions:

recall: polyatomic ions are groups of atoms that can %%behave%% like single atom ions

ex.:

NaCl - regular ionic compound

NH4Cl - polyatomic ionic compound

NH4NO3 - only polyatomic ions

when %%multiple of these are involved in forming a compound%%, they need to be shown as part of a single group (we do so by using parentheses to indicate the polyatomic ions where more than one is needed)

ex.: (NH4)2SO4

naming covalent compounds:

FIRST RULE: DO NOT SIMPLIFY CHEMICAL FORMULAS

we will only be dealing with %%binary molecular compounds%%

prefix naming system - know your prefixes and their associated #’s

1—mono

2—di

3—tri

4—tetra

5—penta

6—hexa

7—hepta

8—octa

9—nona

10—deca

general rules are like naming binary ionic compounds…

- first element keeps its original spelling

- second element is changed to end in –ide

additional rules

- prefixes are required for %%BOTH%% elements to show how many of each atom is in the compound

- the exception is using mono- for the first element (not necessary)

weird naming quirk: for oxide, drop any ending “a” or “o”

%%kinetic molecular theory:%%

gases basics:

- gases have no definite shape or volume and can be compressed

- gas molecules are constantly moving about and have kinetic energy

- %%higher temperatures = more kinetic energy%%

- normal boiling point: the temperature at which a substance changes from liquid to gas at atmospheric pressure

bringing intermolecular forces into the mix:

- intermolecular forces are forces of attraction, which means that to get a liquid to become a gas, you must counter these forces

- requires additional energy, which means that %%the stronger the intermolecular forces in a substance, the higher its boiling point%%

order of strength of IMFs: solid > liquid > gas

kinetic molecular theory (KMT) is a model or theory used to explain the behavior of gases

- describes relationship between pressure; volume; temperature; and velocity, frequency, and force of collisions

main points:

- gases contain particles that are in constant, random, straight-line motion

- gas particles collide with each other and with the container, transferring energy, but not resulting in any loss of energy (perfectly elastic)

- gas particles are very far apart and have negligible volume

- gas particles do not attract each other (no IMFs)

%%gas laws:%%

relationships:

- %%pressure and how much gas you have%%: more gas particles bouncing off the container = more force = more pressure

- %%pressure and volume%%: applying more pressure to gases decreases the amount of space they take up; decreasing the amount of space causes more collisions between gas and container

- %%temperature and pressure%%: temperature is not just proportional to KE, it is defined as a measure of average KE of particles in a substance

(KE = ½ mv^2)

as you increase the temperature, particles hit the container with more energy = more force

- %%temperature and volume%%: as you increase the temperature, gas particles move faster and will exert more force; if you want to maintain the same pressure, you need to expand the container so that less collisions happen

the combined gas law: (p1v1)/t1 = (p2v2)/t2

p = pressure (measured in torr., mmHg, atm, or kPa)

v = volume

t = temperature (measured in K)

1 - situation 1

2 - situation 2

TEMPERATURE MUST BE IN KELVIN

%%behaviors of ideal vs. real gases:%%

real gases:

- particles have volume

- energy lost in collisions

- intermolecular forces

ideal gases:

- particles have no volume

- collisions are elastic

- no interactions between particles

real gases behave like ideal gases: at high temperatures and low pressures

%%our KMT describes an ideal gas.%%

gases are ideal if they behave exactly as predicted.

two assumptions that KMT makes are actually not true of gases:

  1. KMT: gas particles do not attract one another

reality: most of the time, you can ignore attractive forces because they are small. when conditions become extreme, IMFs matter—%%very cold temperature will cause gases to not behave ideally%%

  1. KMT: gas particles do not occupy volume

reality: gas particles have very little volume normally, but when you increase the pressure to extreme amounts, the volume matters—very high pressures will also cause gases to not behave ideally.