Notes, summaries, assignments, exams, and problems for Chemistry

1. Structure of an atom -  An atom is composed of protons, electrons, and neutrons. The entire mass of an atom is concentrated in the nucleus which is at the centre.

   1. Protons - Protons are the positively charged particles which are present in the nucleus of an atom.

   2. Neutrons - Neutrons are the particles in an atom that have a neutral charge. 

   3. Electrons - An electron is a negatively charged subatomic particle that can be either bound to an atom or free

   4. Atomic Mass (what it represents) - The atomic number refers to the number of protons in the atom's nucleus, 

   5. Atomic Number (what it represents) - The atomic mass of an element represent the average total mass of its neutrons, protons, and electrons

2. Standard Atomic Notation

   1. How to determine how many neutrons,

Three major characteristics of life

The cell theory

Three major domains of life

VSEPR — Valence Shell Electron Pair Repulsion

Molecular structure — the three-dimensional arrangement of atoms in a molecule.

Molecular structure and electron-pair repulsion

Electron-pair repulsion: electron pairs spread as far apart as possible to minimize repulsion. Unshared (lone) pairs exert an overall effect on the bond angles between shared electron pairs.

Hybridization

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals that are identical in energy and shape. For example, mixing an s orbital and a p orbital produces two sp hybrid orbitals.

The structure around a given atom is determined by minimizing repulsion between electron pairs.

sp hybridization

• Geometry: Linear
• Bonded atoms: Two bonded
• Lone pairs: Zero non-bonded

Ethers and Epoxides: Reactions, Properties, and Applications

1. Boiling Point Difference: Ethanol vs. Dimethyl Ether

Question: Which provides the best explanation for the large boiling point difference between ethanol (b.p. 78 °C) and dimethyl ether (b.p. -25 °C)?

Correct Answer: The difference in hydrogen bonding (H-bonding).

Note: The molecular weight of both ethanol and dimethyl ether is 46. The significant difference in boiling points is due to ethanol's ability to form strong intermolecular hydrogen bonds, which dimethyl ether cannot.

2. Utility of Crown Ethers

Question: Crown ethers are especially useful for:

Correct Answer: Complexing with metal cations.

3. Product of Cyclohexene and Peroxybenzoic Acid

Question: What is the product of the reaction... Continue reading "Ethers and Epoxides: Reactions, Properties, and Synthesis Mechanisms" »

Scientific Method: Steps and Definitions

Describe each step of the Scientific Method.

Purpose

Ask a question. A clear, testable question defines the focus of investigation.

Hypothesis

Hypothesis: This is an educated guess about what you expect will happen. It should be stated as a testable prediction.

Experiment

Experiment: Design and perform an experiment to test your hypothesis. Include controls and clearly defined variables.

Collect Data

Collect data: Record observations and analyze what the data means. Often you'll prepare a table or graph of the data.

Conclusion

Conclusion: Decide whether to accept or reject your hypothesis. Communicate your results clearly.

Common Measurement Units and Examples

Units (common): Volume: cm³; Length: m, cm; Mass: kg,... Continue reading "Scientific Method Steps and Measurement Units for Physical Science" »

Ductility: Able to undergo change of form without breaking

·Malleability: capable of being shaped, as by Hammering or pressing:

·Density (give an Example): a measurement of how Tightly matter is crammed together. Example: Oil floats on vinegar because Its density is less.

• Chemical properties of matter (give an Example): Are any of the properties Of matter that may only be observed and measured by performing a chemical change or chemical Reaction. Example: oxidation states

·What is a physical Change (give an example): A usually reversible change in the physical 

properties of a substance,as size or shape. Example: When melting an ice cube.

·Difference between Chemical properties and physical properties (give an example)

Ionic Bonding

Bonding between a non-metal and a metal where electrons are transferred from the metal to the non-metal. This results in the non-metal forming a negative ion and the metal forming a positive ion. The structure is a giant ionic lattice with strong electrostatic forces between ions. A lot of energy is needed to break these forces, resulting in high melting and boiling points. Ionic compounds conduct electricity when aqueous or molten, as the ions are free to move around. They can be represented using dot and cross diagrams.

Covalent Bonding

Bonding between two non-metals. Covalent compounds do not conduct electricity as there are no charged particles. Small molecules are liquids or gases at room temperature due to weak intermolecular... Continue reading "Chemical Bonding and Structure" »

Thompson: A Marxist Historian

Thompson was a historian with a Marxist background whose interest in radical political works sets him apart from other authors we studied. He, like Hoggart, followed culturalism, a perspective that stresses human agency, or the active production of culture and not its passive consumption. His book The Making of the English Working Class really embodies the term, since in it he traces the development of the English working class between 1780 and 1832, more or less the time encompassed by the Industrial Revolution. The book can be seen as a rescue operation of the members (especially radicals) of the working class lost in a history led by the deaths of monarchs, statesmen, military leaders, and politicians. These... Continue reading "The Making of the English Working Class: A Radical Perspective" »

Distillation Tower Dynamics and Heat Transfer

After changing a process variable, the tower will reflect this change from top to bottom slowly. Each tray of a tower has a different temperature and vapor pressure than any other tray in the tower.

Flooding occurs when the liquid flow in the downcomers and onto the trays is too high, or when the vapor flow is too high. Heat is removed from the tower when hot or warm overhead and bottom products exit the tower, and through leaks in insulation.

Approximately 85% of the distillation tower heat is supplied by the reboiler. Heat sources for a distillation tower include:

• Radiant heat
• Sparging
• Reboilers

Tray Design and Liquid Flow

A downcomer is a device that allows liquid to flow from one tray to another between... Continue reading "Distillation Tower Operations and Furnace Fundamentals" »

Alkali Metals

Lithium

• Lithium is harder than other alkali metals.
• It has higher melting and boiling points than other alkali metals.
• It is the least reactive alkali metal.
• It is a strong reducing agent compared to other alkali metals.
• It is the only alkali metal that forms its monoxide.
• It is not capable of forming solid hydrogen carbonates, unlike other alkali metals.
• It does not react with ethyne to form ethynide, while other alkali metals do.
• It reacts slowly with bromine compared to other alkali metals.
• It is the only alkali metal that reacts with nitrogen to give lithium nitride (Li₃N).

Alkaline Earth Metals

Beryllium

• Beryllium is harder than other members of its group.
• It has higher melting and boiling points than other members of its group.
• Its electronegativity