What is organic chemistry?
The chemistry of carbon and its compounds. The living world is largely composed of carbon-based compounds.
What are the 3 primary attributes of carbon?
1. It's stable ∴ can form long carbon chains containing hundreds of atoms
2. Has 4 valence e⁻ ∴ forms a lot of bonds (including branched chains)
3. Is small ∴ facilitates the existence of multiple bonds
What is an ionic bond? Give an example.
Electrostatic bond between a cation and an anion. Eg. NaCl
What are the properties of ionic compounds? (5 points)
1. Dissolves easily in H₂O
2. The sum of the + charges must equal the sum of the - charges
3. Conduct electricity
4. High melting points
5. Often ions are arranged in a 3D crystal lattice (which is more favourable for the cmpd as the + and - ions will attract each other).
What is a covalent bond? Give an example.
The bond that results in the sharing of an e⁻ pair(s) between 2 atoms. The sharing can be equal or unequal depending on the electronegativity of the 2 atoms.
Eg. HCl or CH₄
What are the properties of covalent compounds? (6 points)
1. Molecules with no net charge
2. May be solid liquid or gas
3. Solubility in H₂O depends on polarity (i.e. Like dissolves like and since water is a polar solvent and most covalent compounds are fairly nonpolar, many covalent compounds don't dissolve in water.)
4. Does not conduct electricity well
5. More flammable than ionic compounds
6. much lower MP and BP than ionic compounds (b/c no bonds to break, just IM forces to get through)
What state do the group 1 (except H), group 2, and aluminum exist in?
Group 1 = +1 (except H)
Group 2 = +2
Aluminum = +3
Halogens can exist in ________ or _________. When halogens are in an ionic compound, what is their charge?
ionic or covalent bonds. -1.
How do we know if an ionic bond exists?
If it has a group 1 or 2 element (except H), or aluminum and, of course, any of the polyatomic ions.
The tendency of an atom to draw shared electrons toward itself.
When the elecronegativity charge of a compound is 0, what is it termed? What if it is between 0 and 1.7? Finally, what if it is above 1.7?
0 = non-polar
Btwn 0 and 1.7 = polar
Above 1.7 = ionic
What is important about connectivity? How does this relate to drawing of the lewis structure?
It tells us which atoms are bonded to which. The chemical formula often tells us how the lewis structure should be drawn.
What is a saturated hydrocarbon and what is their formula?
Compounds containing only carbons and as many H atoms that they can possibly hold. Formula is: C(n)H(2n)+2
Saturated hydrocarbons don't have ___________.
C=C double bonds
When you have the same chemical formula, but different connectivity, what is it called? Explain how this can work with C₅H₁₂.
Eg. C₅H₁₂ can be either Pentane or 2-methylbutane
Often in hydrocarbons, a halogen will substitute for a _________. What is this called?
hydrogen. It's called a halogenated hydrocarbon
When there are 2 or more carbon atoms in a molecule, each carbon retains what kind of shape if bonded to 4 other atoms?
1. How do you determine where the charge lies in a molecule?
2. What is the formula for calculating the formal charge for an atom within a molecule?
How do you get this information?
1. Calculating the formal charge for each atom.
2. Formal charge = (# of valence e⁻) - (# of nonbonding e⁻) - ¹/₂(# of bonding e⁻)
*** Must draw lewis structure to determine this information
Ethylene is said to __________ b/c it is "missing" 2 hydrogens. How does this appear in the structural formula?
contain one unit of unsaturation. It appears as a double bond or a ring in the structural formula.
2 "missing" H atoms corresponds to what?
one unit of saturation
What are resonance contributors (RCs)?
They have the same connectivity, but different lone e- pairs & different multiple bonds.
What are the 6 rules for determining the importance of resonance contributors?
1. All RCs must have the same # of e⁻ & the same charge, but the formal charges can change.
2. RCs where octet rule is obeyed are more imp than in those where octet rule is not obeyed.
3. RCs with more covalent bonds are more imp than those with less.
4. The more formal charges (separation of charge) on a structure, the less important it is. 5. RCs containing like charges (+,+ or -,-) in adjacent atoms are not favoured.
6. The most important RC has a - charge on the more electronegative atom.
What is an isomer?
Compounds that have the same chemical formula but different connectivities. They may differ in their chemical and physical properties.
What are the two types of isomers? Define them.
Constitutional Isomers and Stereoisomers.
Constitutional Isomers: differ in the order and way in which the atoms are bonded together. They have different connectivities.
Stereoisomers: Have the same connectivities, but differ in the arrangement of their atoms in space. They can only be distinguished in 3D.
The more atoms in a molecule the _____ the # of possible structures it can create.
Define bond length.
The avg distance btwn the nuclei of the atoms that are covalently bonded together.
Define bond angle.
The angle formed by the intersection of two covalent bonds at the atom common to both.
How do you determine a molecule or polyatomic ion's shape?
Use VSEPR theory, which states:
1. Count each ond around the central atom (whether single, double, or triple) as one VSEPR pair.
2. Count each lone pair around the central atom as one VSEPR pair.
2 of VSEPR pairs equals what shape & bond angles?
3 of VSEPR pairs equals what shape & bond angles? What about 4, 5 and 6
2 VSEPR pairs: Linear & 180°
3 VSEPR pairs: Trigonal planar & 120°
4 VSEPR pairs: Tetrahedral & 109.5°
5 VSEPR pairs: Trigonal Bipyramid & 90°, 120°
6 VSEPR pairs: Octahedral & 90°
Electronegativity increases as you go from _____ to _____ and _____ in a group. The most electronegative elements are therefore found in the _________ corner of the periodic table.
left to right and up
Non-polar covalent bond means that...
e⁻ are shared equally between 2 atoms.
Polar Covalent bond means that...
e⁻ are shared unequally between 2 atoms.
The presence of polarity can be indicated in two different ways. What are they?
1. By writing partial positive δ+ and partial negative δ- charges over the bonded atoms OR
2. By drawing a bond dipole arrow (the point of the arrow is drawn toward the more electronegative end).
Intermolecular forces are...? They increase as...? What are the three types if IM forces?
the forces that act btwn molecules. They increase significantly as the weight and size of the molecules increase.
3 types: Dipole/Dipole, London Dispersion, and Hydrogen Bonding
In comparison to covalent bonds, IM forces are _______.
What is H-bonding important for determining?
the solubility of organic compounds in water. Molecules that have H-bonding will dissolve in water if the polar part of the molecule is not too large. *** Non-polar molecules DO NOT dissolve in water.
What type of HC is this: H - C Ξ C - H ? Explain.
How many units of unsaturation does it have? How is this known?
It's an unsaturated HC (an alkyne) and it has two units of unsaturation. We know this b/c it has 2 additional bonds. Alkenes and alkynes are unsaturated because they are capable of adding a hydrogen (or two) when the C=C (CΞC) bond is broken.
List the 4 exceptions to the octet rule.
* H only has 2 e⁻
* S and P can have more than 8 e⁻
* B can have 6 e⁻
If you were asked to find the most important and least important resonance structures, how would you go about solving this problem?
1. Determine how many valence e⁻ there are in a chemical formula (i.e. CH₂CHO⁻ has 18)
2. Draw the lewis structures w/ formal charges
3. Find out if they all obey the octet rule?
4. Find out if there is an equal separation of charge.
5. Find out if there are like charges on adjacent atoms.
6. Finally, see if there is a - charge on the the more electronegative structure.
1. If less energy is required to overcome IM forces (i.e. b/c they are weaker) what does this mean for predicting boiling point?
2. The _________ the IM force, the higher the boiling point.
1. Weaker IM forces, easier to overcome ∴ less energy required = lower boiling point
Greater surface area equals ____ boiling point.
Different constitutional isomers (same chemical formula) can have different boiling points. How can you predict which is higher between different isomers?
Draw the lewis structure and looking at the IM forces. The shape and size will help to determine how they affect the the BP. Eg. More surface area = higher boiling point.
What are the two exceptions to the tetrahedral shapes of molecules? In these cases, they are tetrahedral, but their angle sizes are different.
NH₃ (107.5°) and H₂O (104.5°)
What are Dipole/Dipole foces and how do they work?
1. D/D only occurs in polar molecules.
2. Many molecules have permanent dipoles (slightly + & slightly - portions). The + ends of polar molecules will be attracted to the - ends of other molecules. This results in a D/D attractive force that holds molecules together.
Any substance with strong Dipole/Dipole forces has to absorb substantially more energy in order to melt and boil. Explain.
Polar substances tend to have higher melting and boiling points than similar non-polar substances since they require greater amts of energy input to overcome D/D forces.
Explain the London Dispersion Forces. (3 points)
1. It's the only IM force in non-polar molecules.
2. Weakest of all IM forces
3. B/c e⁻ shift around, it's possible in polar molecules, from time to time, for one side to have a teeny tiny partial + and another side could have a teeny tiny partial -. This is where the LD force is at play. The + are drawn to the -.
The more e⁻ a molecule has (or the larger it is), the ________ it's London Disperson. This correlates to __________ melting and boiling points.
Large atoms and molecules (those which contain more e⁻) are more easily ________ than smaller ones. Therefore, they have stronger __________________.
polarized. LD forces.
LD, like D/D forces are effective only at _______________________.
Explain the Hydrogen Bond IM forces.
It's the strongest of the 3 IM forces.
H will be bonded to a small EN atom (*** only N, O or F). This way it is at the end of a very polar covalent bond.
The H atom will be attracted to negative ends of nearby polar molecules.
What is surface tension?
Pertains to the top-most layer of liquid. The liquid-air interface.
Surface molecules have no "neighbours" above to counteract the downward pull of those below, and the unbalanced forces provide the surface with special properties not found in the rest of the liquid. These forces cause a "tightening" of the liquid surface (like elastic). Like any elastic, the surface resists stretching and makes itself as small as possible - this causes liquids to be spherical (since its the smallest surface area for the volume).
The surface tension of molecules is _______ with IM forces. More surface tension = ___________________.
pulled down, more IM forces.
The larger the molecule, the _______ the boiling point.
H-Bonding has a significant impact on the ___________ & ___________ of molecules. Explain.
melting and boiling points. Hydrogen bonding is the strongest intermolecular attractive force. It causes the melting and boiling points to be elevated since the molecules are more attracted to each other and thus require more energy to break apart.
Ethanol (C₂OH) mixes in H₂O in all proportions meaning it is ___________.
Explain the inverse relationship between polarity of a HC chain and its solubility in water.
As the non-polar HC chain increases, the solubility in water decreases. Like dissolves like so polar (i.e. OH) will dissolve in water, but non-polar (i.e. HC) will not. The longer the NP part, the less dissolvable the substance will be.
What are the guidelines for naming binary compounds? (3 points) *** How do the rules change with it's ionic compounds vs covalent compounds?
1. Element that appears first retains its elemental name.
2. The second element begins with a root derived from its elemental name and ends with the suffix - ide.
3. When there is more than one atom of a given element in the formula, the name of the element usually contains a prefix that specifies the number of atoms present.
*** Ionic compounds: Only use 1st two rules ∴ no numerical prefixes
*** Covalent compounds: Use all three rules.