Chapter 2: Atoms & Elements

Classification of Elements

Elements are classified based on their properties and position on the periodic table. Understanding these classifications is essential for predicting chemical behavior.

• Metals: Located on the left and center of the periodic table. They are typically shiny, good conductors of heat and electricity, malleable, and ductile.

• Nonmetals: Found on the right side of the periodic table. They are generally poor conductors, not shiny, and can be gases, liquids, or brittle solids at room temperature.

• Metalloids: Elements with properties intermediate between metals and nonmetals. They are found along the staircase line (e.g., Si, B, As).

Groups and Periodic Table Nomenclature

Certain columns (groups) on the periodic table have specific names and characteristic properties.

• Group 1A: Alkali metals

• Group 2A: Alkaline earth metals

• Group 7A: Halogens

• Group 8A: Noble gases

Predicting Ionic Charge

The charge of ions formed by elements can often be predicted based on their group number.

• Group 1A: +1 charge

• Group 2A: +2 charge

• Group 7A: -1 charge

• Group 6A: -2 charge

Transition metals may have variable charges.

Moles and Avogadro’s Number

The mole is a fundamental unit in chemistry for counting particles (atoms, molecules, ions).

• Avogadro’s Number: particles per mole

• Conversions: Use Avogadro’s number to convert between moles and number of particles.

Example: To find the number of atoms in 2.0 mol of carbon:

Molecular Weight (Molar Mass)

The molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol).

• Calculation: Add the atomic masses of all atoms in the chemical formula.

Example: For H2O:

Chapter 3: Molecules and Compounds

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. The main types are:

• Ionic Bonds: Formed between metals and nonmetals via transfer of electrons.

• Covalent Bonds: Formed between nonmetals via sharing of electrons.

• Metallic Bonds: Occur between metal atoms, involving a 'sea' of delocalized electrons.

Example: NaCl is ionic; H2O is covalent; Cu is metallic.

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 present.

• Empirical Formula: Simplest ratio (e.g., CH2O for glucose)

• Molecular Formula: Actual composition (e.g., C6H12O6 for glucose)

Naming Compounds

Compounds are named according to systematic rules:

• Binary Ionic Compounds (Type I): Metal (fixed charge) + nonmetal (add -ide)

• Binary Ionic Compounds (Type II): Metal (variable charge) + nonmetal (add -ide); indicate metal charge with Roman numerals

• Covalent Compounds: Use prefixes (mono-, di-, tri-, etc.) to indicate number of atoms

• Ionic Compounds with Polyatomic Ions: Name the cation and the polyatomic anion (e.g., NaNO3 is sodium nitrate)

Writing Chemical Formulas from Names

Use the rules of nomenclature to write the correct chemical formula for a given compound name.

• Example: Magnesium chloride = MgCl2

Percent Composition (Mass %)

Percent composition expresses the mass percentage of each element in a compound.

• Formula:

Example: In H2O, %H =

Calculating Empirical Formulas from Percent Composition

Steps to determine the empirical formula from percent composition:

1. Assume 100 g of compound (so % = grams).

2. Convert grams to moles for each element.

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

Determining Molecular Formula from Empirical Formula

To find the molecular formula, compare the empirical formula mass to the molar mass of the compound.

• Formula:

• Multiply subscripts in empirical formula by n.

Chapter 4: Chemical Reactions and Chemical Quantities

The Seven Diatomic Elements

Certain elements exist naturally as diatomic molecules (two atoms bonded together):

• H2, N2, O2, F2, Cl2, Br2, I2

Mnemonic: "Have No Fear Of Ice Cold Beer"

Physical State Symbols in Chemical Equations

Symbols indicate the physical state of substances in chemical equations:

• (s): solid

• (l): liquid

• (g): gas

• (aq): aqueous (dissolved in water)

Balancing Chemical Equations

Balancing ensures the same number of each atom on both sides of the equation, reflecting the law of conservation of mass.

• Adjust coefficients (not subscripts) to balance atoms.

• Start with the most complex molecule.

Example:

Combustion Reactions of Hydrocarbons

Combustion of a hydrocarbon involves reaction with oxygen to produce carbon dioxide and water.

• General Equation:

• Always produces CO2 and H2O as products.