3: Energy Connections
- Page ID
- 206551
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- Introduction to energy.
- 3.2: Representing Valence Electrons with Dots
- The Lewis Structure of a molecule shows how the valence electrons are arranged among the atoms of the molecule. Lewis electron dot diagrams use dots to represent valence electrons around an atomic symbol. Lewis electron dot diagrams for ions have less (for cations) or more (for anions) dots than the corresponding atom. From experiment, chemists have learned that when a stable compound forms, the atoms usually have a noble gas electron configuration or eight valence electrons.
- 3.3: Covalent Bonds
- Covalent bonds are formed when atoms share electrons. Lewis electron dot diagrams can be drawn to illustrate covalent bond formation. Double bonds or triple bonds between atoms may be necessary to properly illustrate the bonding in some molecules.
- 3.4: Drawing Lewis Structures for Covalent Compounds
- Lewis dot symbols provide a simple rationalization of why elements form compounds with the observed stoichiometries. A plot of the overall energy of a covalent bond as a function of internuclear distance is identical to a plot of an ionic pair because both result from attractive and repulsive forces between charged entities. In Lewis electron structures, we encounter bonding pairs, which are shared by two atoms, and lone pairs, which are not shared between atoms.
- 3.5: Introduction to Organic Molecules
- Organic chemistry is the study of the chemistry of carbon compounds. Organic molecules can be classified according to the types of elements and bonds in the molecules.
- 3.6: Resonance
- Resonance structures are averages of different Lewis structure possibilities for the same molecule.
- 3.7: Air Pollutants
- We breathe the air everyday. What is in our air? What should we be concerned about? How do we test to ensure that the air we breathe keeps us safe?
- 3.8: Naming Molecular Compounds
- Molecular compounds are inorganic compounds that take the form of discrete molecules. Examples include such familiar substances as water and carbon dioxide. These compounds are very different from ionic compounds like sodium chloride. Ionic compounds are formed when metal atoms lose one or more of their electrons to nonmetal atoms. The resulting cations and anions are electrostatically attracted to each other.
- 3.9: Chemical Equations
- A chemical reaction is the process in which one or more substances are changed into one or more new substances. Chemical reactions are represented by chemical equations. Chemical equations have reactants on the left, an arrow that is read as "yields", and the products on the right.
- 3.10: How to Write Balanced Chemical Equations
- In chemical reactions, atoms are never created or destroyed. The same atoms that were present in the reactants are present in the products - they are merely reorganized into different arrangements. In a complete chemical equation, the two sides of the equation must be present on the reactant and the product sides of the equation.
- 3.11: The Mole
- The mole is a key unit in chemistry. The molar mass of a substance, in grams, is numerically equal to one atom's or molecule's mass in atomic mass units.
- 3.12: Stoichiometry
- Chemical equations also provide us with the relative number of particles and moles that react to form products. In this section you will explore the quantitative relationships that exist between the quantities of reactants and products in a balanced equation. This is known as stoichiometry. Stoichiometry, by definition, is the calculation of the quantities of reactants or products in a chemical reaction using the relationships found in the balanced chemical equation.
- 3.13: Mole-to-Mole Conversions
- Previously, you learned to balance chemical equations by comparing the numbers of each type of atom in the reactants and products. The coefficients in front of the chemical formulas represent the numbers of molecules or formula units (depending on the type of substance). Here, we will extend the meaning of the coefficients in a chemical equation.
- 3.14: Making Molecules- Mole to Mass (or vice versa) and Mass-to-Mass Conversions
- We have used balanced equations to set up ratios, now in terms of moles of materials, that we can use as conversion factors to answer stoichiometric questions, such as how many moles of substance A react with so many moles of reactant B. We can extend this technique even further. Recall that we can relate a molar amount to a mass amount using molar mass. We can use that ability to answer stoichiometry questions in terms of the masses of a particular substance, in addition to moles.
- 3.15: Exothermic and Endothermic Processes
- All chemical reactions involve changes in energy. This may be a change in heat, electricity, light, or other forms of energy. Reactions that absorb energy are endothermic. Reactions that release energy are exothermic.
- 3.16: Enthalpy
- Enthalpy changes are a measure of the energy changes in chemical reactions. The energy involved in a particular reaction depends on the quantity of the substances involved. Enthalpy changes for reactions can be estimated using average bond energies.
- 3.17: Temperature and Heat
- Three different scales are commonly used to measure temperature: Fahrenheit (expressed as °F), Celsius (°C), and Kelvin (K).
- 3.18: Calorimetry
- The specific heat of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by 1 degree Celsius.
- 3.19: Climate Change - Too Much Carbon Dioxide
- Carbon dioxide is the primary greenhouse gas emitted through human activities. In 2015, carbon dioxide accounted for about 82.2% of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals).