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CREATED BY: Alistaire Rauch THE ULTIMATE CHEMISTRY STUDY GUIDE TERM TWO: UNIT II: SMELLS I. Smells Chemical Compounds smell certain ways because they bind with nose receptors in different ways causing a different smell. (The odor molecule is bonded with a neuron receptor which travels to the brain to perceive a certain scent). Molecular Formula/Molecular Covalent Compound: A chemical formula of a molecular substance that tells the types of atoms and the number of different type of atoms Isomers: Molecules that have the same chemical formula, but different structures overall not just the rotation of certain branches etc. Different types of smells Ending of Name Chemical Formula Patterns Functional Group/Other Info SWEET -ate -yl - Usually contains 2 O atoms, 1 O in others. - Stringy - hydroxyl - ester PUTRID -ic...acid - 2 O atoms in ALL - stringy - carboxyl MINTY -one - Contains 1 O atom in ALL - frying pan shaped - ring structures - ketone - hydroxyl FISHY -ine - Contains 1 nitrogen atom in ALL - stringy - amine CAMPHOR (don’t think this knowledge is needed) - double ring structure - 1 O atom in all - ball shaped - examples: fenchol, camphor - ketone - hydroxyl II. HONC RULE The Honc Rule states the number of covalent bonds the main molecules can make. Hydrogen - 1 Bond Oxygen - 2 Bonds Nitrogen - 3 Bonds Carbon - 4 Bonds Valence Electrons Covalent Bonds Formed Electrons needed for full shell Hydrogen 1 1 1 Oxygen 6 2 2 Nitrogen 5 3 3 Carbon 4 4 4 III. Bonding In molecular structures that are drawn out, a single bond is represented by “a line” which is the sharing of one pair of valence electrons. A double bond or sharing of two valence electrons is shown by two lines. Triple bond is three pairs of electrons shared and shown by three lines. IV. Isomers An isomer is molecules that have the same chemical formula, but different structures overall not just the rotation of certain branches etc. An example of two isomers would be the fact that they both share the same formula of C 4H 10 . One way that an isomer is considered different is by looking at the main structure or “backbone” of a molecule or in this case the carbons. In butane, there are four carbons together in a single straight chain (continuous chain) while in isobutane, there is a three carbons, while the fourth is in the middle and pokes out. In other words, this can be compared to a train going down a rail, in butane, there is four straight carbons without being interrupted, while in isobutane, there is three carbons, but in order to get to the last carbon that sticks out one would have to backtrack or take a turn. V. Lewis Dot Structures: A Lewis Dot Structure is a relatively accurate way to represent valence electrons being bonded with other atoms as well as lone pairs. Lone pairs are electrons that are not being bonded. On itself a lewis dot structure of an element just shows the valence electrons The way to draw a lewis dot structure (molecules) is: 1. Draw the total number of valence electrons of atoms 2. Put a pair of electrons between each of the bonded atoms 3. Place the remaining electrons between the double/triple bonds or as lone pairs In this example, the lone pairs are the electrons that are on the outside. The bonded ones are represented in between the molecules. This table shows the first 6 periods of lewis dot structures. There is also a common pattern where elements in the same groups have the same number of valence electrons Octet Rule: This rule is for nonmetal atoms and when they combine that each atom must have a total of eight valence electrons by sharing electrons. This picture to the right is an example of the octet rule and how each molecule has a total of 8 valence electrons VI. Functional Groups This is just an overview of the main groups, these molecules are not a hundred percent accurate because different forms can exist of each group. A functional group is a group of molecules that molecules have in common. Example: Carboxyl Group: This is a functional group that is normally associated with putrid smelling molecules. This group is composed of mainly an oxygen double bonded with a carbon along with a oxygen and hydrogen. Oxygen = Carbon - Oxygen - Hydrogen Ester Group: This group is normally associated with sweet smelling molecules. This is made out of an oxygen and carbon double bonded along with a oxygen and carbon. Oxygen = Carbon - Oxygen (- Carbon) Amine Group: This group is associated with the fishy smelling molecules. This is made out of a nitrogen and carbon. Nitrogen - Carbon Ketone Group: This group is associated with the minty smelling molecules. This is composed an oxygen and carbon double bonded, along with the carbon attached to two other molecules in a single bond. Oxygen = Carbon -----( -Carbon -carbon w/ oxygen - Carbon -R) Aldehyde Group: This group is associated with sweet smelling molecules (perfume and flowery). This group has an oxygen and carbon double bonded along with another carbon and hydrogen. Hydroxyl Groups: This group is made of a hydrogen and oxygen bonded. An important compound that contains this group would be alcohols and this normally smells medicinal and or alcoholic. Alkane Group: This functional group is contains one carbon with four different bonds (seen in methane). This group can either have no smell or a gasoline smell. An important note about this group is that the molecular formula follows this rule: C nH 2n+2 . Examples are shown in the picture to the right. Molecules also do not follow the exact groups listed above, but tend to share features and they are called: Esters ⇒ Ethers Name Compound Type Functional Group Smell -ane alkane alkyl no smell/gasoline smell -ic acid carboxylic acid carboxyl putrid -yl -ate ester ester sweet -one ketone ketone minty -ol alcohol hydroxyl medicinal -lamine amine amine fishy VII. Naming Acids: An acid is named by the number of carbons in its main backbone or chain. When an acid is combined with an ester it follows this: _____-yl _____-ate VIII. Electron Domains: An electron domain the space occupied by valence electrons in a bonded pair of electrons, a lone pair of electrons, or multiple bonded pairs. Electron Domain Theory is the tendency for electrons to be as far apart as possible (also called VSEPR or Valence Shell Electron Pair Repulsion). IX. Space Fillings Models: A space filling model is a three dimensional representation of a chemical substance that mainly displays the position of the bonds and the atoms itself. It is also used to determine the overall structure. Long/Stringy- Sweet Frying Pan- Minty Ball-Shaped- Camphor X. Polar and Nonpolar Molecules: Partial Charges- A less than full charge on part of a molecule, created by the unequal sharing of electrons. Polar Molecules: Molecules attracted to a charge because they have a partial change on them. For example, this water molecule, has a partial negative and partial positive charge. In other words a polar molecule has two poles. Nonpolar Molecule: A nonpolar molecule is a molecule that is not attracted to another charge. It also is a molecule that shares electrons equally. Intermolecular Forces: A force of attraction that occurs between molecules XI. Electronegativity: Electronegativity: The tendency of an atom to attract shared electrons that are involved in bonding and it is the measurement of the ability of a molecule or atom to attract other electrons to itself. Dipole: A molecular or covalent bond with a nonsymmetrical distribution of electrical charge that makes the molecule or bond polar. A crossed arrow is used to show the direction of a dipole. The crossed end represents the partial positive charge and the arrow is the negative end. ELECTRONEGATIVITY CHART: This chart displays the elements and their electronegativities respectively. It is important to know that fluorine is the most electronegative and francium is the least. Also, the pattern of how it increases bottom to top and left to right. Intra versus Inter: Intermolecular forces occur between two molecules, and intramolecular forces occur within the molecule. London Dispersion Forces: It is the weakest intermolecular force. It is a force between two nonpolar molecules, noble gase, and some charges. Ex: Dipole-Dipole: The attraction of two partially opposite charges (polar bond). ( Ex. Hydrogen Bonding: This is an intermolecular force between two molecules, where a hydrogen connects to an oxygen, nitrogen, or fluorine of another molecule. RULE: R-H------:B-R Hydrogen atom (H) must link to a nitrogen, oxygen, or fluorine (B) of another molecule. XII. How to decide if a molecule is overall polar The way to decide if a molecule is overall polar is to first look at the overall structure and whether it has symmetry around the central molecule because then it the molecule would cancel out the dipoles. A good example would be C F 4 . This molecule is symmetric and the dipoles would cancel each other out. If it asymmetric, this would mean that bonds don’t cancel out. Another way to think about this is to look out whether there is potentially more lone pair electrons in one area than in another. For example in C F 4 , they are evenly displaced around each molecule and visually it is overall equal because each fluorine is equally distanced from the other fluorines that have lone pairs. So therefore, it is nonpolar. While water on the hand, has a buildup of lone pairs in one and it is not evenly displaced therefore it is polar because it has a greater chance to bond. (Extra Material) Ozone O3 is a weird molecule because of it does not follow the double bonding rule (if it did it would be a triangle shape) and instead has two electrons that are moving throughout the structure because it will make the molecule more stable. This molecule looks like the “actual” one to the right. This molecule is polar because there is a greater group of lone pair electrons on the right and left which can creates a partial negative on the left and right. On the top of the molecule it has a partial positive because there are less electrons. XII. Polar and Nonpolar Substances and Solubility: Polar Molecules easily dissolve in other polar substances such as water and alcohol. Since water is polar and so is alcohol, they form hydrogen bonds through and this causes it to easily dissolve into water. On the hand polar and nonpolar do not mix well, but nonpolar and nonpolar do mix well. A good example would be water and oil, a polar and nonpolar substance. Nonpolar and nonpolar molecules do attract each other and dissolve each other. Summary: Polar + Polar = Mix/Dissolve Nonpolar + Nonpolar = Mix/Dissolve Polar + Nonpolar = NO mix Nonpolar + Polar = NO mix LIKE DISSOLVES LIKE! XIII. Phase, Size, Polarity etc. Molecule Smell Phase Small Nonpolar Molecules Yes Gas Small Polar Molecules Yes Gas Medium-Sized Polar and Nonpolar Molecules Yes Liquid Large Polar and Nonpolar Molecules No Solid Ionic No Solid Metallic No Solid Network Covalent No Solid This chart displays the Molecule and its type along with the smell and phase. Concerning that of Polar or Nonpolar molecules, the size is determined by number of carbons: Molecules (Nonpolar and Polar) # of Carbons Small X>5 Medium 5 < X < 19 Large X > 19 XIV. Mirror-image Isomers Mirror-Image Isomers are molecules whose structures are mirror images of each other and cannot be superimposed on one another and due to their different 3D structures contain different properties and scents. Superimposed means that a molecule can be oriented in a way to fit the original molecule. A good example from class is D-Carvone and L-Carvone. The simple way to determine if a molecule has a mirror isomer is to see whether a carbon is surrounded or bonded to four very different groups. This does not mean a carbon is bonded to a oxygen, fluorine, and two hydrogens, it has to be four different molecules or R groups. XV. Amino Acids and Proteins Amino acids are molecules that contains an amine (-NH2) and a carboxylic acid (-COOH) functional group. A long strand of perhaps thousands are called proteins, but these proteins are folded into a very complex specific 3D shape. When two amino acids bond, they bond in a similar way to ester synthesis where a water molecule is created as a byproduct. With this, when the long strands of amino acids fold with the hydrophilic (polar) side facing outwards and hydrophobic (nonpolar) side inwards. The bond is called a peptide bond. In the human body, there are twenty different amino acids all of which contain a “left handedness”, the reason left handed amino acids are used and not right is undiscovered, but it may be because of how most the amino acids falling to space are more left than right. To determine whether an amino acid is polar or nonpolar is to look at the R group of the molecule and whether that R group is overall polar or nonpolar and the bond type as well. Amino Acids also contain a “chiral” molecule which means that the molecule is not superimposable and is thus a mirror-image isomer. It is just another way to say a mirror-image isomer. A “chiral center” is the carbon molecule surrounded by four different groups (mirror-image isomer. Achiral means an object that superimposable on its mirror image. For example, like tetrafluoromethane (CF4). Fun fact: chiral in Greek means “hand.” Your hand by the way, is not superimposable. For an explanation better than the one I can give, check out Sal Khan: https://www.khanacademy.org/science/organic-chemistry/stereochemistry-topic/chirality-r-s-syst em/v/introduction-to-chirality (change speed to 1.25 or more if you feel like he talks too slow). XVI. CORN CORN is a mnemonic to determine if an amino acid is right or left handed. First you would want to look at the molecule from a side view, and because they contain an amine (-NH2) and a carboxylic acid (-COOH) functional group, it would would tetrahedral overall. So look at it with the hydrogen in the middle or sticking out at you. Then, if you go LEFT to right from CO group and it spells CORN, then it would be LEFT handed. IF it goes to the RIGHT and spells corn, it would be RIGHT handed.