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Gen Chem Notes 2018 (Sem 1)
General Chemistry I (1010 251)
Rochester Institute of Technology
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General ChemistryPreview text
8-29-18 (The Foundations of Chemistry)
All substances are constructed of molecules and chemistry is the study of those molecules
Physical properties: Nothing happens to the chemical properties. Things molecules do where they don’t change physical propositions 1. State of matter 2. Boiling point 3. Freezing point 4. Solubility 5. Malleability 6. Electrical conductivity 7. Heat conduction 8. Tensile strength
What is the reactivity of the molecules?
Will they form new substances with A, B, or C? How fast is the reaction? Products more stable than reactants? What is the yield? Does it create or require energy? Use or generate electrons? Any by products? What is the structure of the new material?
Chemical properties and change involve an actual change in composition and physical properties and change involve a constant composition
Iron rusting v. water boiling Fe v. H2O FeO v. H2O
An experiment requires measurement and measurement comes in two types Qualitative - did you make the right stuff? Aspirin isn't the same as insulin Quantitative - how much of something do I have (mass)? How big is it (Volume)?
Numbers are just numbers, its the Units that are important
Units provide the context for numbers and the ability to convert units is a fundamental, and useful way to solve simple problems.
“Pure Units” Mass (kg) Length (m) Time (s) Charge ©
“Derived Units” Using multiple pure units Speed (m/s) Volume (m^3)
Units turn things into information/data and the more specific the number the better.
Significant figures are how many important digits there are in a number and they are the amount of digits you either round to or drop when adding, subtracting, multiplying, or dividing.
8-31-18 (Sig Figs)
You can always measure to one more significant figure that what you can see. For example if you have a ruler with only inches on it and a green block goes 40% between 2 and 3, you can say that it measures 2 inches.
2 inches must always be written as 2 inches if its data 2 inches = 2 inches = 2 inches but not for data The number of digits written represents the number of digits measured and known!
123 = 3 sig figs 100. = 1 sig fig and 2 place markers
Subscripted numbers/lines over numbers = not significant
1020.
First 0 is significant because it’s between 1 and 2. The second 0 is a place marker
Scientific notation writes every number as #.#### multiplied by some space marker For example 2 x 10^2 pounds would represent my weight to 2 sig figs The 10^# marks the position, so I don’t need any extra zeros lying around
200 = 1 sig fig 2 x 10^2 = 3 sig figs
Start ??? Finish 73 inches ----- =? feet ??? THE PATH
Put the unit you want to get rid of on the bottom of the fraction Put the unit you want on the top of the fraction
32mg ?lb lead _____ ??? = _____
mL water gal water
Your final answer should be in 2 sig figs because you start with 32 mg which is 2 sig figs
9-7-18 (Sig Fig Rules and Basic Chem)
Calculating Sig Figs rules
2 different rules... 1. Multiplication / Division - The answer has the same number of sig figs as the digit with the least number of sig figs
1 x 12 = 12
- Addition / Subtraction - The answer has the same last decimal place as all digits have in common
1 + 2 + 1 = 16 (16 rounded)
1^2 + 1^3 + 6^
If you have multiple steps in a problem, you don’t round until the end, but you do apply the rule. Write things with subscripts where the significant things are normal and the not significant things (the numbers you would usually round off) are subscripts.
You can multiply or divide any units together You can’t add or subtract numbers with different units
Density is the mass to volume ratio of a substance. It allows you to compare the relative “heaviness” of two materials. A larger density material means that a sample of the same size (volume) will weigh more. D = M/V
Ex. The density of aluminum is 2/mL. If i have a block of aluminum that is 1 meter on each side, then what is the mass of the block? 1. Find the volume of the cube 2. Go from m^3 to mL b/c 1m=100cm and 1cm^3 = 1m^ 3. Now you can get rid of mL and just have g which is the mass (You have to convert each meter to a cm, not all at once)
Building blocks of matter Chemistry is the study of matter - which is anything that has mass and takes up space. Matter itself has a wide variety of properties.
What world we see around us appears to be quite divisible - it can be divided into pieces of the whole. Grind up a toothpick, you get sawdust. Sawdust is a piece of a toothpick which is a piece of 2x4 which is a piece of a tree.
A molecule (chemical compound) is the smallest unit of matter that is indivisible by physical means and divisible by chemical means. Molecules are made up of even smaller units called atoms (elements). An atom is indivisible by any normal chemical or physical means. Chemistry is all about how you arrange and rearrange atoms to make different molecules. Chemistry is also about the physical properties of the molecules themselves. When we talk about the physical properties of materials, we are talking about molecules. When we talk about chemical properties we talk about the atoms. More than one type of molecule mixed together is called a mixture.
Matter
Can you physically separate it? No - Pure yes - Mixture
Can you chemically separate is? Is it uniform throughout? No - atom yes - Molecule No - heterogenous yes - homogeneous Helium Pure water Mixed rocks Tea with sugar
9-10-18 (Atoms, Molecules, and Ions)
Atomic structure - chemistry is the study of physical and chemical properties of materials. The study of material properties does not require an understanding of underlying atomic and molecular structure - but it can be helpful.
Construction of matter: 1. Atoms are physically indivisible matter 2. Molecules are collections of atoms that are joined together 3. Mixtures are collections of different molecules that are intertwined with each other
- Number of protons determines identity of atom
- The electrons are responsible for the chemistry of the atom
Mass Number: The mass number is the total number of neutrons and protons. It is related to the atomic mass of an atom, but isn’t directly connected. Just an integer that represents total number of protons and neutrons
Atomic Mass/weight: Atomic mass has units of “atomic mass units” (AMU). An amu is an arbitrary unit of mass, it is relative to carbon-12 having a mass of 12 amu. Typically, the atomic mass is a little less than mass number, so a mass number of 24 will usually have an atomic mass of 23. 99 amu. This is the weighted average of all of the naturally occurring isotopes.
Atomic Number: The number of protons the atom possesses. All atoms of a particular type must have the same number of protons. It is the proton number that determines the identity of the atom. Carbon is atomic number 6 because all carbon atoms have 6 protons. You know it must be carbon.
Isotopes: All carbon atoms must have 6 protons, but they can have different numbers of neutrons. Adding neutrons will change the mass number. An isotope is a type of atom with a particular mass number. Carbon-12 Carbon-13 Carbon-
12
C - top number is the mass number and the bottom is the atomic number 6
Ions - An atom (or compound) that has an unequal number of protons and electrons.
13 + C = 6 protons, 5 electrons, 7 neutrons 6
13 - C = 6 protons, 7 electrons, 7 neutrons 6
O,A,Se,Te,Po,Lv are the chalcogenides
Neon has 3 different naturally occurring isotopes
20Neon - mass = 19 amu - 90% 21Neon - mass = 20 amu - 0% 22Neon - mass = 21 amu - 9%
But they aren’t equally common
Natural Abundance All isotopes occur with a certain “natural abundance” - the % of a sample of that element that has isotope mass
(19)(0) + (20)(0) + (21)(0) = 20 amu 1. Take the atomic mass of the isotope 2. Multiply it by the % of abundance divided by 100 3. Add all of the isotopes x abundances together
Molecules from atoms Molecules are made by combining 2 or more atoms and it makes no difference whether they are the same of different atoms
If you have one mole of any element, then its mass in grams is the same as its atomic mass in amu
2Mg + O2 ---------> 2MgO 2 atoms of Mg combined with one molecule of oxygen makes 2 molecules of MgO
9-14-18 (Electronic Structure of Atoms)
What is light? Light is an oscillating electromagnetic wave
2 ways to look at any wave: Freeze the wave and walk along it Stay put and watch the wave go by
Distance between the two peaks is called the wavelength The number of times it goes up and down in a second (hour, minute, day) is called frequency and this is abbreviated v
Combining these gives you a distance
Wavelength (velocity) = c
c = 3^8m/s is the speed of light in a vacuum
You will get 1/s which is Hz
Light is just another form of energy..
When light strikes matter, it can do 3 things 1. Reflects 2. Refracts 3. Goes straight through
Absorbing light becomes a means of probing matter Different wavelengths of light interact with different things 1. Infrared light interacts with vibrations of bonds (Makes vibrations faster) 2. Microwave lights interact with rotations of bonds (Makes water rotate faster) 3. Visible or ultraviolet light interact with the electrons
The bohr model and the photoelectric effect... Absorbing UV or visible light moves the electrons to a higher electron state
Suppose I need 10^-18 J of energy to knock an electron off. This is called the work function of a material: the smallest amount of energy that will cause an electron to be emitted. It turns out that light energy is not additive in the way normal heat is. It comes prepackaged in single waves called “photons”
E = hf E = h(c/wavelength)
E = 6^34Js (3^8/600x10^-9m)
(Go back and look in notes for HW)
The nucleus is encased in electrons. The nucleus is stable and unchanged and you have to change energy levels in one step.
The electron “orbits” are stable and electrons can move between them by absorbing light
1/wavelength = R (1/m^2 - 1/n^2)
- Light is just energy
- If light is absorbed, it has to be tuned to a specific energy transfer
- In a quantum world, only certain discrete energy levels are allowed. You can not slowly decay in an orbit until you crash into the nucleus
- Electron orbitals are diffuse, “probability cloud” a. Electron orbitals are 95% probability intervals b. Allowed electron orbitals are determined by 4 quantum numbers i. S = round ii. P = teardrop
n = principal quantum number (1,2,3,4,5...) orbital layers around the nucleus l = angular momentum quantum numbers (0,1,2,3,4...(n-1)) it specifies the type of orbital within the same shell (in each n there is 0 to n-1 orbitals) ml = magnetic quantum number (-l, -l+1, -1, 0, 1) Orientation of the orbital ms = spin quantum number (-½, ½ ) magnetic spin of the electron
l depends on n and ml depends on l
n=1, l=0, ml=0, ms=-½
n=1, l=0, ml=0, ms=½
2s is the next lowest - it takes 2 electrons 2p comes next - it takes up to 6, so it gets the last 2 electrons
1s^2, 2s^2, 2p^
Mg - 12 electrons
1s^2, 2s^2, 2p^6, 3s^
Makes it have less energy which is good (works for s-d and d-f) ..^2, 3d^ ..^1, 3d^
..^2, 3d^ ..^1, 3d^
Rows are the n values -----> Blocks are the l values
9-19-18 (Ions and Electron Configurations Cont.)
Core v. Valence
Core are the non-reactive ones Valence are the reactive ones
Fe0 - 26e- [Ar] 4s2, 3d Fe2+ - 24e- [Ar] 4s0, 3d
Fe3+ - 23e- [Ar] 3d
O0 - 16e- [He] 2s2, 2p O2- - 18e- [He] 2s2, 2p6 or [Ne]
Paramagnetism - only atoms with unpaired electrons are attracted to magnetic fields
Carbon
1 1 1 1 1 1
1s 2s 2p
Paramagnetic. Only until 2p has 4 electrons, it will not pair up.
9-21-18 (Different Rules / Different Universe)
- Pauli exclusion principle a. No 2 electrons have the same quantum number
- Aufbau principle - lowest energy levels fill up first
If you changed the rules, everything changes
9-24-18 (Chemical Compounds)
Chemical symbols - The symbols in the periodic table are just abbreviations for the names of the different elements. It is easier to write C than carbon
Molecular Symbols - Water, for example, is made up of 2 hydrogen atoms stuck to 1 oxygen atom, so it is written H2O
I could describe a chemical reaction using words... Two diatomic molecules and one diatomic oxygen molecule will react under XYZ conditions and form 2 water molecules
2H2 + O2 ------> 2H2O
Chemical nomenclatures is the systematic naming of chemical compounds so that chemical symbols can be translated into names and names into symbols
Identifying metals and nonmetals is important to this
9-28-18 (Chemical Compounds Cont.)
4NO2 + 6H2O ----> 4NH3 + 7O
Four moles of nitrogen dioxide and 6 moles of dihydrogen monoxide react to yield 4 moles of ammonia and seven moles of oxygen
2Mg + O2 ----> 2MgO
2 atoms of Mg combine with 1 molecule of oxygen to form 2 molecules of MgO
36 grams of Carbon, how many moles do I have?
(36) (1mol / 12) = 2 mol
Molar mass should be viewed as a conversion factor between mass and moles
I have 36 of water (H2O), how many water molecules is that
To get the molar mass, you need to add the mass of 2 hydrogen to the mass of 1 oxygen = 18 g/mol
(36)
10-1-18 (Lewis Dot Structures)
- Total number of valence electrons - the total number of valence electrons must be accounted for, no extras and none missing
- Octet rule - every atom should have an octet (8) electrons associated with it. Hydrogen should only have 2 (a duet)
In a molecule, there are only 2 types of atoms: 1. Central = bonded to more than one other atom 2. Terminal = bonded to only one other atom You can have more than one central atom in a molecule
You can have multiple bonds Single, double, triple
Determining Lewis dot structure: 1. Determine the total number of valence electrons 2. Determine which is the “central” atom a. “Leftmost” or “downmost” atom and hydrogen is never the central atom 3. Stick everything to the central atom using a single bond 4. Fill the octet if every atom by adding dots 5. Verify the total number of valence electrons in the structure 6. Add or subtract electrons to the structure by making/breaking bonds to get the correct number of valence electrons 7. Check the “formal charge” of each atom 8. If you have a double bond look for resonance
“Formal charge” isn't a real charge. It is a pseudo-charge on a single atom
Formal charge = number of valence electrons - number of bonds - number of nonbonding electrons = number of valence = number of lines = number of dots
This is ideally 0
For H2O
FC (H) = 1-1-0 = 0 FC (O) = 6-2-4 = 0
10-3-18 (LDS and Resonance)
Single bonds = long Double bonds = short Triple bonds = shorter than double
Resonance - when you have this, the real structure is not any one of the individual structures but the combination of all of them. You can always recognize the resonance - there are double or triple bonds involved. If you take the 3 different CO2 structures, the “average” is the original one we drew
10-5-18 (LDS)
Trying to represent delocalization of electrons in Lewis Dot structures
Look at his lewis slides for nitrite
Resonance = delocalization = overlap of p orbitals
- Incomplete octets - less than 8 electrons ex. H, B, Be, Li
- Expanded octets - more than 8 electrons ex. Phosphorus and Sulfur and anything with D orbitals
You are trying to get 0 on the leftmost downmost atom, or the middle atom, or the most electronegative atom and to achieve this you might need resonance
Ionic compounds - attraction between ions of opposite charges Na+ Cl- Covalent compounds - sharing of electrons between adjacent atoms PF
10-12-18 (Electron and Molecular Geometry)
Electronegativity if the ability of an atom to attract electrons to itself and it is important in predicting whether a bond is covalent or ionic
Only O has an electronegativity of 3.
O (EN = 3) N (EN = 3) Unequal sharing
EN change = larger EN - smaller EN
EN change = 0 - 0 = non-polar covalent EN change = 0 - 1 = polar covalent EN change = 2+ = ionic
Cl - Cl EN = 3.0-3 = 0 Non-polar
H - Cl EN = 3.0-2 = 0. Polar
Na - Cl EN = 3.0-0 = 2. Ionic
Polarity is represented as an arrow
H = +
Cl = - HCl
Polarity is a vector, it has size and direction. You can’t separate the two. The arrow points away from the positive atom and towards the negative atom
What holds molecules together? Bonds!
Valence shell electron pair repulsion VSEPR
Electrons hate each other and nonbonding pairs hate each other more than bonds
CO2 - always linear because the oxygens want to be far away from them COH2 - always trigonal planar because the hydrogens will be on both sides and the only place for the oxygen is up or down
Not all bonds are the same
Electron Geometry 2 electron groups = linear = 180 degrees 3 electron groups = trigonal planar = 120 degrees 4 electron groups = tetrahedral = 109 degrees 5 electron groups = trigonal bipyramidal = 90 and 120 degrees 6 electron groups = octahedral = 90 degrees
The angles are “sort of” predictable
What you have to do is add number of bonds and number of lone pairs on the central atom for the first group. The number of bonds on the central atom is second and number of lone pairs on the central atom is third.
Molecular Geometry
Gen Chem Notes 2018 (Sem 1)
Course: General Chemistry I (1010 251)
University: Rochester Institute of Technology
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