Chemistry 110 Exam 3 Study Guide: Chemical Reactions, Electrons, and Bonding

Chapter 8: Quantities in Chemical Reactions

Mole to Mole Conversions

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. Mole-to-mole conversions use balanced chemical equations to determine how many moles of one substance react with or produce another.

• Mole Ratio: The coefficients in a balanced equation indicate the ratio of moles of each substance.

• Example: For the reaction $2H_2 + O_2 \rightarrow 2H_2O$, 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

Mass to Mass Conversions

Mass-to-mass conversions involve converting the mass of a reactant or product to moles, using the mole ratio, and then converting back to mass.

• Steps:

  1. Convert mass to moles using molar mass.

  2. Use mole ratio from the balanced equation.

  3. Convert moles back to mass.

• Formula: $\text{mass} \rightarrow \text{moles} \rightarrow \text{moles} \rightarrow \text{mass}$

Conservation of Mass, Enthalpy (Exothermic/Endothermic)

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Enthalpy changes indicate whether a reaction absorbs or releases heat.

• Exothermic Reaction: Releases heat ($\Delta H < 0$).

• Endothermic Reaction: Absorbs heat ($\Delta H > 0$).

• Equation: $\Delta H = \text{H}_{\text{products}} - \text{H}_{\text{reactants}}$

Limiting Reactant and Percent Yield

The limiting reactant is the substance that is completely consumed first, limiting the amount of product formed. Percent yield compares the actual yield to the theoretical yield.

• Limiting Reactant: The reactant that determines the maximum amount of product.

• Theoretical Yield: The maximum possible amount of product.

• Percent Yield Formula: $\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

• Example: If 10 g of product is obtained but 12 g is expected, percent yield is $\frac{10}{12} \times 100\% = 83.3\%$.

Chapter 9: Electrons in Atoms and the Periodic Table

Light and the Electromagnetic Spectrum

Light is a form of electromagnetic radiation, which includes a range of wavelengths from radio waves to gamma rays.

• Electromagnetic Spectrum: Includes radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma rays.

• Visible Light: Wavelengths from about 400 nm (violet) to 700 nm (red).

Orbital Theory and Electron Configurations

Electrons occupy orbitals in atoms according to specific rules, which determine the arrangement of electrons (electron configuration).

• Orbital: A region of space where an electron is likely to be found.

• Electron Configuration: The arrangement of electrons in an atom, e.g., $1s^2 2s^2 2p^6$ for neon.

• Aufbau Principle: Electrons fill the lowest energy orbitals first.

Periodic Trends

Periodic trends are patterns in properties of elements across periods and groups in the periodic table.

• Atomic Size: Decreases across a period, increases down a group.

• Ionization Energy: Increases across a period, decreases down a group.

• Metallic Character: Increases down a group, decreases across a period.

Chapter 10: Chemical Bonding

Ionic and Covalent Compounds

Chemical bonds form when atoms share or transfer electrons. Ionic bonds involve electron transfer; covalent bonds involve electron sharing.

• Ionic Compounds: Formed from metals and nonmetals; electrons are transferred.

• Covalent Compounds: Formed from nonmetals; electrons are shared.

• Lewis Structures: Diagrams showing valence electrons and bonding.

Resonance Structures

Some molecules have more than one valid Lewis structure, called resonance structures.

• Resonance: Delocalization of electrons across multiple structures.

• Example: Ozone ($O_3$) has two resonance structures.

Determining Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule. It is determined by the number of electron clouds around the central atom.

• VSEPR Theory: Valence Shell Electron Pair Repulsion theory predicts shapes based on electron cloud repulsion.

Electronic Geometry Table

Number of electron dense clouds	Geometric Name	Geometric Structure
2	Linear	Atoms arranged in a straight line
3	Trigonal Planar	Atoms arranged in a flat triangle
4	Tetrahedral	Atoms arranged in a pyramid with four faces

List of possible Molecular Geometries: Linear, Bent, Trigonal Planar, Tetrahedral, Trigonal Pyramidal

Electronegativity and Polarity

Electronegativity is the ability of an atom to attract electrons in a bond. Polarity arises when atoms with different electronegativities share electrons unequally.

• Electronegativity: Increases across a period, decreases down a group.

• Polar Covalent Bond: Electrons are shared unequally.

• Nonpolar Covalent Bond: Electrons are shared equally.

• Example: Water ($H_2O$) is a polar molecule due to the difference in electronegativity between hydrogen and oxygen.