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

Chemical Change vs. Phase Change

Chemical change: Produces new substances that didn't exist before.

Phase change: The substance remains the same before and after the process.

Dissolving: It is only a homogeneous mixture; no new substances appear.

Identifying Chemical Changes

How do we know if a chemical change is occurring?

• Gas release: Gases may not be visible; we identify them by bubbles in a liquid.
• Color change
• Thermal energy change
• Energy release as light

Understanding Chemical Reactions

A chemical reaction occurs when the starting substances, called reactants, transform into other new substances, called products.

The appearance of new substances is due to the rearrangement of the reactant's atoms, forming the products. The information about a chemical... Continue reading "Chemical Reactions and Their Impact on Industry" »

Ozone (O3 ) is a made with three oxygen atoms; it is very unstable and has a short lifetime. At room Temperature and pressure has acrid odour and no colour, although at high concentration levels can turn Into blue. At high concentrations can be toxic and can cause death. It s not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. VOC + NOx + sunlight tropospheric O3Particulate Matter (PM) "Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small Particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic... Continue reading "Divergence in the upper air results, near the surface in: atpl" »

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,

The Four Fundamental States of Matter

• Solid: Characterized by structural rigidity and resistance to changes of shape or volume.
• Liquid: A form of matter between a gas and a solid that has a definite volume but no definite shape.
• Gas: An air-like fluid substance which expands freely to fill any space available, irrespective of its quantity.
• Plasma: A state of matter made from a gas that has lost its electrons due to heat (e.g., the Sun, stars, lightning).

Particle Arrangement

• Solid: Particles are tightly packed, usually in a regular pattern. Solids vibrate (jiggle) but generally do not move from place to place.
• Liquid: Particles are close together with no regular arrangement. They vibrate, move about, and slide past each other.
• Gas: Particles are well-

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)