Covalent Bonds and Molecular Structures: Key Concepts
Covalent Bonds and Molecular Structures
Types of Covalent Bonds
- Non-polar Covalent Bonds: Electronegativity difference is close to zero (less than 0.4).
- London Dispersion Force: Weak attraction between nonpolar molecules; the more electrons, the greater the attraction.
- Polar Covalent Bonds: Electronegativity difference is between 0.4 and 1.67. The higher the difference, the more polar the bond.
Dipole Moment
A dipole moment (polar molecule) is a molecule that has a center of positive charge and a center
Read MoreAldol Condensation: Reactions, Mechanisms, and Types
Aldol condensation is a condensation reaction in organic chemistry in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by dehydration to give a conjugated enone. Aldol condensations are important in organic synthesis because they provide a good way to form carbon-carbon bonds. For example, the Robinson annulation reaction sequence features an aldol condensation; the Wieland-Miescher ketone product is an important starting
Read MoreFundamental Concepts in Chemistry: Matter, Energy, and Measurement
Fundamental Concepts in Chemistry
Observations, Hypothesis, Experiment, and Theory
- Observations: Facts obtained by observing and measuring events in nature.
- Hypothesis: A statement that explains an observation.
- Experiment: A procedure that tests the hypothesis.
- Theory: A model that describes how the observations occur by using experimental results.
Significant Figures
- Leading zeros: Preceding non-zero digits in decimal numbers are not significant.
- Exact number: A number obtained by counting or by definition.
Pure Substances and Mixtures: Properties and Separation Methods
Pure Substances and Mixtures
There are some characteristic properties that serve to identify substances (density, conductivity, color) and some general properties common to all types of matter (mass, volume, etc.). The main division of matter is into pure substances and mixtures. Pure substances have specific properties that characterize them, mixtures do not. The determination of any specific property of a substance is the best way to know if this substance is pure or not.
Pure Substances
Pure substances
Read MoreAlkyne, Alkene, and Addition Reactions: A Detailed Analysis
Alkynes
Alkynes are hydrocarbons containing at least one triple bond, forming a homologous series with the empirical formula CnH2n-2. The C-H bond in ethyne is more polar than in other C-H bonds, allowing ethyne to act as a weak acid. The simplest and most important alkyne is ethyne, which has a triple bond, a high electron density, and sp-hybridized orbitals. These sp-hybrid orbitals have a higher s-character than sp2 and sp3 orbitals. The bond length of the C-C and C-H bonds is shorter than in
Key Concepts in Stellar Evolution and Astronomy
Properties of Stars and Matter
Opacity of Gas: The resistance of matter to the passage of radiation, which depends on the temperature.
Stellar Model: A table of numbers representing the conditions in various layers within a star.
Nuclear Forces: The two forces of nature that only affect the particles in the nuclei of atoms.
Nuclear Fission: Reactions that break the nuclei of atoms into fragments.
Nuclear Fusion: Reactions that join nuclei to form more massive nuclei.
Coulomb Barrier: The electrostatic
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