General Chemistry: Fundamental Concepts, Nomenclature, and Problem Solving

Basic Topics in General Chemistry

Metric System Prefixes

The metric system uses prefixes to indicate multiples or fractions of base units. Understanding these prefixes is essential for unit conversions in chemistry.

• Kilo- (k): $10^3$

• Centi- (c): $10^{-2}$

• Milli- (m): $10^{-3}$

• Micro- (\mu): $10^{-6}$

• Nano- (n): $10^{-9}$

Example: 1 kilometer (km) = 1000 meters (m).

Names and Symbols of Elements

Each chemical element is represented by a unique one- or two-letter symbol. These symbols are used universally in chemical equations and formulas.

• H: Hydrogen

• O: Oxygen

• Na: Sodium

• Cl: Chlorine

Example: The formula for water is H2O.

Names and Formulas of Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded. They play a key role in the nomenclature of ionic compounds.

• Sulfate: SO42−

• Nitrate: NO3−

• Phosphate: PO43−

• Ammonium: NH4+

Nomenclature of Ionic and Covalent Compounds

Chemical nomenclature is the system for naming chemical substances. Ionic compounds are named using the cation and anion names, while covalent compounds use prefixes to indicate the number of atoms.

• Ionic Compounds: Name the cation first, then the anion (e.g., NaCl is sodium chloride).

• Covalent Compounds: Use prefixes (mono-, di-, tri-, etc.) to indicate the number of each atom (e.g., CO2 is carbon dioxide).

Composition of the Atom: Protons, Neutrons, and Electrons

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons. The number of protons defines the element.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

Example: Carbon-12 has 6 protons, 6 neutrons, and 6 electrons.

Chemical Composition: Empirical and Molecular Formulas

The empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula gives the actual number of each atom in a molecule.

• Empirical formula: CH2O for glucose

• Molecular formula: C6H12O6 for glucose

Stoichiometry and Limiting Reactants

Stoichiometry involves the calculation of reactants and products in chemical reactions. The limiting reactant is the substance that is completely consumed first, limiting the amount of product formed.

• Balanced equation: Shows the relative amounts of reactants and products.

• Limiting reactant: Determines the maximum amount of product.

Example: In the reaction $2H_2 + O_2 \rightarrow 2H_2O$, if you have 3 moles of H2 and 1 mole of O2, O2 is the limiting reactant.

Conversions and Problem Solving

Unit Conversions and Dimensional Analysis

Unit conversions are essential for solving chemistry problems. Dimensional analysis uses conversion factors to change units.

• Example: To convert 1120 feet/second to miles/hour:

$\frac{1120\ \text{ft}}{1\ \text{s}} \times \frac{1\ \text{mile}}{5280\ \text{ft}} \times \frac{3600\ \text{s}}{1\ \text{hr}} = 764\ \text{miles/hr}$

Density and Mass Calculations

Density is defined as mass per unit volume. It is used to relate the mass and volume of a substance.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Example: Gold has a density of 19.3 g/cm3. To find the volume of gold you can buy with $5000 at $2590 per Troy ounce:

1 Troy ounce = 31.1 g; $\frac{5000}{2590} = 1.93$ Troy ounces; $1.93 \times 31.1 = 60.0$ g; $\frac{60.0\ \text{g}}{19.3\ \text{g/cm}^3} = 3.11$ cm3

Nomenclature

Naming Ionic Compounds

Ionic compounds are named by stating the cation first, followed by the anion. The table below summarizes the process for several compounds.

Name	Formula	Cation	Anion
sodium iodide	NaI	Na+	I−
potassium sulfide	K2S	K+	S2−
calcium chloride	CaCl2	Ca2+	Cl−
lithium oxide	Li2O	Li+	O2−
iron(III) sulfate	Fe2(SO4)3	Fe3+	SO42−
copper(I) oxide	Cu2O	Cu+	O2−
aluminum bromide	AlBr3	Al3+	Br−
lead(II) chloride	PbCl2	Pb2+	Cl−
potassium phosphate	K3PO4	K+	PO43−
nickel(III) nitride	NiN	Ni3+	N3−
silver carbonate	Ag2CO3	Ag+	CO32−
cobalt(II) sulfide	CoS	Co2+	S2−
nickel(II) iodide	NiI2	Ni2+	I−
nitrogen dioxide	NO2	N/A	N/A
cesium oxide	Cs2O	Cs+	O2−

Additional info: Some entries inferred for completeness.

Empirical and Molecular Formulas

Empirical Formula Determination

The empirical formula is determined from the percent composition of a compound. For example, palmitic acid has 74.94% C, 12.58% H, and 12.48% O by mass.

• Convert percentages to grams (assume 100 g sample).

• Convert grams to moles for each element.

• Divide by the smallest number of moles to get the simplest ratio.

Example: For palmitic acid: C: 74.94 g / 12.01 g/mol = 6.24 mol; H: 12.58 g / 1.01 g/mol = 12.46 mol; O: 12.48 g / 16.00 g/mol = 0.78 mol. Divide by 0.78 to get the ratio.

Molecular Formula Determination

The molecular formula is found by comparing the empirical formula mass to the molar mass.

• Formula: $n = \frac{\text{Molar mass}}{\text{Empirical formula mass}}$

• Multiply the subscripts in the empirical formula by n.

Stoichiometry and Limiting Reactants

Balancing Chemical Equations

Balancing equations ensures the law of conservation of mass is obeyed. Each side of the equation must have the same number of atoms of each element.

• Example: $C_2H_5OH (l) + O_2 (g) \rightarrow CO_2 (g) + H_2O (g)$

• Balanced: $C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O$

Limiting Reactant and Mass Calculations

To determine the mass of product formed, identify the limiting reactant and use stoichiometry to calculate the theoretical yield.

• Convert grams of reactants to moles.

• Use the balanced equation to find the mole ratio.

• Calculate the mass of product using molar mass.

Decomposition Analysis

Empirical Formula from Experimental Data

When a compound is decomposed and the masses of products are measured, the empirical formula can be determined by converting the masses to moles and finding the simplest ratio.

• Example: A liquid containing C, O, and Cl reacts to form CO2 and HCl. The masses of CO2 and HCl are used to determine the moles of C, H, and Cl in the original compound.

Additional info: This process is fundamental in analytical chemistry for determining unknown compounds.