Notes - Summary Foundations of Chemistry PDF

Preview

Summary

CHE144 Summary Notes...

Description

MATTER

Write an equation that gives the relationship between the speed of light, frequency and wavelength. Describe this relationship in a sentence as well. The equation is c = λν where c is the speed of light, λ is the wavelength and ν is the frequency. The product of wavelength and

Explain the meaning of the term’s photon and quantum. Write the equation for the energy of a photon or quantum and explain the relationship between energy and frequency of electromagnetic radiation. The terms both describe quantities or bundles of energy that behave like tiny particles. The energy of a photon or quantum is represented by the equation E = hν where E is the energy of the photon or quantum, h is Planck’s constant and ν is the frequency of the radiation. Energy can only be absorbed or emitted by atoms in multiples of h. The energy is directly related to the frequency of the radiation, the Write a description of Neil’s Bohr’s proposal to explain the appearance of line spectra for gases in a sealed tube with high voltage applied. Neils Bohr proposed that electrons move in circular orbits around the nucleus of an atom. The orbits and the electrons that occupy them have specific or quantized energy levels. To be excited to a higher allowed energy level, electrons must absorb a specific amount of energy. To transition back to the lower allowed energy level, that same amount of energy must be emitted. The presence of lines with specific wavelengths in a line spectrum is evidence for the absorption and subsequent emission of specific amounts of energy. What were the most important ideas to come out of Neils Bohr’s work? That electrons exist only in certain discrete energy levels and that energy is involved in moving an electron from one level to another Briefly explain why the concept of orbital hybridisation was developed. model of covalent bonding involving overlap of atomic orbitals explained the bonding in simple molecules such as HF and Cl2, but was inadequate for more complex molecules such as CH4, NH3, PF5. The shapes of these molecules could not be explained by overlap of atomic orbitals. The model of hybridisation was developed to explain the Lewis structures

Electron and Molecular geometry E and Z If line of high priority crosses the double bond then E, Z is on same side of double bond S and R R is clockwise, S is anticlockwise Chromophore A chromophore is a part of a molecule that will absorb electromagnetic radiation. That radiation could be in the UV, visible, IR, or any other range. For example, if a compound absorbs wavelengths in the UV range then it is said to have a UV chromophore – a double bond or series of double bonds are Delocalization All the C atoms in the benzene molecule are in the sp2 hybrid state. The π electrons are not fixed between pairs of C atoms and can appear in the alternate pattern. The result is a ‘resonance hybrid’ electron structure where the bonds between the C atoms in benzene are more than single bonds and less th d bl b d Conjugation Conjugation refers to the arrangement of double and/or triple bonds in a molecule. If double bonds are effectively next to each other the π electrons can ‘delocalise’ across that part of the molecule that contains the double bonds, thus allowing the molecule to absorb different wavelengths of electromagnetic energy compared to that when the electrons are localised in only one bond. The result is that the molecule Substituents Priority –CH3 4 –CH2CH3 3 –CH=CH2 2 –CH2OH 1 Substituents Priority –CH2CH3 4 –C≡CH 3 –C≡N 2 –CH2OCH3 1 ⇌ can absorb Beer-Lambert Law The equation that represents the Beer-Lambert Law is A =  l c Where A = Absorbance,  = molar absorptivity (L mol–1 cm–1 ), l = path length of radiation through the sample (in cm), and c = concentration (in mol L–1 ). Absorbance is directly proportional to , l and c. Example An environmental chemist analyses mine waste water for iron(III) by stabilising the iron(III) as a complex of acetohydroxamic acid, which absorbs at 424 nm. The chemist takes a 10.0 mL sample of the waste water, complexes the iron(III) and makes the sample up to a final volume of 100.0 mL in a volumetric flask. The resulting solution has an absorbance of 0.505 at 424 nm when measured in a standard 1 cm cuvette. The iron(III) complex has a molar absorptivity of 2.583 × 103 L mol–1 cm–1 . Determine the concentration in milligrams per litre (mg L–1 ) of the iron in the original waste water sample.

ORGANIC Newman projections – ClCH2CH2Cl

Amines The chemistry of amines is dominated by the lone pair of electrons on the nitrogen atom. Amine nitrogen atoms are electron rich and thus nucleophilic Amines are also weak bases as they are proton acceptors. Naming Amines

Amide

Nucleophile and Electrophile

Groups Amino acid - contain both an amine and carboxylic acid functionality. Building blocks for peptides and proteins. Nucleic acid - consist of organic base and a sugar, sometimes phosphate. Building blocks of DNA and RNA. Carbohydrate - sugars = polyhydroxy aldehydes and ketones Because the arrangement of the 5/6 membered chain allows a reversible intramolecular cyclisation to occur. A compound where an intramolecular reaction between an aldehyde and an alcohol can occur Lipid - any molecule that is fat soluble. Formally “naturally occurring substances that can be extracted from cells and tissues by non-polar solvents” A compound that is only extractable from biological material with a non polar solvent Peptide - polymer containing less than 50 amino acids Alcohol - Alcohols and phenols are capable of donating a proton (as shown in the equation) but not accepting a

Electrophile: A chemical species that is electron deficient and may accept a pair of electrons to form a new covalent bond Nucleophile: A chemical species that is electron rich and may donate a pair of electrons to form a new covalent bond

Saponification The aggregation of soap molecules (or fatty acid salts) in aqueous solution is all about intermolecular forces. The charged carboxylate group can participate in hydrogen bonding interactions with the water molecules, while the hydrocarbon chains aggregate together to minimise interactions with water. The self-assembled aggregate is called a micelle, which may be represented using a diagram as shown below. Micelles exert their cleaning action by trapping other hydrophobic molecules within their hydrophobic core. Non-polar grease and dirt molecules thus become dissolved in the aqueous solution and removed from the skin, clothing or surfaces.

Fatty acid...