Periodic Table and Classification of Elements

Major Classifications of Elements

The periodic table organizes elements based on their atomic structure and properties. Elements are classified as metals, nonmetals, or metalloids, each with distinct physical and chemical characteristics.

• Metals: Good conductors of heat and electricity, malleable, ductile, shiny, and tend to lose electrons easily.

• Nonmetals: Variable phase, poor conductors, and tend to gain electrons during chemical changes.

• Metalloids: Exhibit intermediate properties and are often used as semiconductors.

Groups and Periods

Elements are arranged in columns called groups or families and rows called periods. Main groups are labeled with "A" and Roman numerals I–VIII, while transition groups are labeled with "B" and Roman numerals I–X.

• Alkali Metals: Group 1A, highly reactive.

• Alkaline-earth Metals: Group 2A, reactive.

• Noble Gases: Group 8A, nonreactive.

• Halogens: Group 7A, very reactive.

• Chalcogens: Group 6A.

• Lanthanides and Actinides: Inner transition metals.

Periodicity

The properties of elements repeat periodically across the table, reflecting similar chemical and physical behaviors within groups.

Predictable Ions and Diatomic Elements

Formation of Ions

Atoms can lose or gain electrons to form ions. Cations are positively charged (lost electrons), while anions are negatively charged (gained electrons). The charge of common ions is predictable based on their group location.

• Group 1A: 1+ charge

• Group 2A: 2+ charge

• Group 3A: 3+ charge

• Group 6A: 2– charge

• Group 7A: 1– charge

Seven Diatomic Elements

Some elements naturally occur as diatomic molecules, meaning they consist of two atoms bonded together. These are:

• Hydrogen (H2)

• Nitrogen (N2)

• Oxygen (O2)

• Fluorine (F2)

• Chlorine (Cl2)

• Bromine (Br2)

• Iodine (I2)

Mnemonic: Have No Fear Of Ice Cold Beer

Chemical Bonding and Compound Types

Ionic and Covalent Compounds

Compounds are formed by chemical bonds between elements. There are two main types:

• Ionic Compounds: Formed by a metal cation and a nonmetal anion (or polyatomic ion). The bond is an electrostatic attraction. Ionic compounds are neutral overall.

• Covalent (Molecular) Compounds: Formed by two nonmetals sharing valence electrons. The bond involves electron sharing between atomic orbitals.

Bond Formation

Ionic bonds are pure charge attractions, while covalent bonds involve a balance of attraction and repulsion between nuclei and electrons.

Formula Mass, Molar Mass, and Mole Calculations

Formula and Molar Mass

The formula mass (or molecular mass/weight) is the sum of the atomic masses of all atoms in a molecule or formula unit. The molar mass is the mass in grams of one mole of a substance, numerically equivalent to the formula mass in g/mol.

• Example: Mass of 1 molecule of H2O = 2 × 1.01 amu (H) + 1 × 16.00 amu (O) = 18.02 amu

• Molar mass of H2O = 18.02 g/mol

Moles and Molar Mass

Moles are used to relate mass to the number of particles. One mole contains 6.022 × 1023 particles (Avogadro's number).

• 1 mole = 6.022 × 1023 atoms or molecules

• Molar mass is the average atomic mass from the periodic table in g/mol

Example Calculations

• To find the number of atoms in a sample: $\text{Number of atoms} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \times 6.022 \times 10^{23}$

• To convert atoms to mass: $\text{Mass (g)} = \text{number of atoms} \times \frac{\text{molar mass (g/mol)}}{6.022 \times 10^{23}}$

Chemical Nomenclature

Types of Compounds and Naming Rules

Chemical nomenclature is the system for naming compounds. The rules depend on the type of compound:

• Type I: Metal + Nonmetal or polyatomic ion (no transition metals except Zn, Ag, Cd)

• Type II: Transition metal + nonmetal or polyatomic ion

• Type III: Nonmetal + nonmetal (covalent compounds)

• Acids: Binary acids (H + nonmetal in aqueous solution), Oxyacids (H + polyatomic ion)

• Hydrated ionic compounds: Ionic compounds with water molecules

Naming Ionic Compounds (Type I and II)

• Type I: Name the metal, then the nonmetal with -ide ending. Example: Na3N is sodium nitride.

• Type II: Name the transition metal with its charge in Roman numerals, then the nonmetal with -ide ending. Example: Ti(SO4)2 is titanium(IV) sulfate.

Naming Molecular Compounds (Type III)

Use prefixes to indicate the number of atoms:

• mono = 1 (usually omitted for the first element)

• di = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, nona = 9, deca = 10

• Example: P2O5 is diphosphorus pentoxide

• Example: CO is carbon monoxide

Naming Acids

Acids are molecular compounds that release H+ ions in water. There are two main types:

• Binary acids: H + nonmetal (aq). Name as "hydro" + base name of nonmetal + "ic acid". Example: HBr (aq) is hydrobromic acid.

• Oxyacids: H + polyatomic ion. If the ion ends in -ate, use "ic acid"; if it ends in -ite, use "ous acid". Example: H2SO4 is sulfuric acid, H2SO3 is sulfurous acid.

Naming Hydrated Ionic Compounds

Hydrates are ionic compounds with a specific number of water molecules. Use prefixes to indicate the number of water molecules.

• MgSO4 • 7H2O: magnesium sulfate heptahydrate

• CoCl2 • 6H2O: cobalt(II) chloride hexahydrate

• CuSO4 • 5H2O: copper(II) sulfate pentahydrate

Sample Calculations and Practice Problems

Atoms, Mass, and Mole Calculations

• To find the number of atoms in a sample: $\text{Number of atoms} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \times \text{number of atoms per mole}$

• To find the mass from the number of molecules: $\text{Mass (g)} = \text{number of molecules} \times \frac{\text{molar mass (g/mol)}}{6.022 \times 10^{23}}$

• To convert between mass, moles, and number of atoms: $\text{mass (g)} \rightarrow \text{moles} \rightarrow \text{number of atoms}$

Example Table: Prefixes for Molecular Compounds

Example Table: Common Ion Charges

Practice Problems

• How many total atoms are present in two molecules of mercury(II) iodate?

• What is the mass of 1.45 × 1030 molecules of COF2?

• How many formula units are present in 65.0 g of FeS?

• How many moles are in 25.0 mL of acetone (CH3COCH3)? Density = 784 kg/m3.

• A sample contains 8.371 × 1021 molecules and has a mass of 0.888 g. What is the molar mass?

• What is the molar mass of oxalic acid dihydrate?

• What is the density of acetic acid if 0.250 moles of CH3COOH has a volume of 14.3 mL?

• How many moles of oxygen are present in 0.089 g of sulfuric acid?

• What is the volume occupied by 0.145 moles of alumina if the alumina has a density of 3.97 g/mL?

Summary Table: Types of Compounds and Naming Rules

Additional info: Academic context was added to clarify naming conventions, periodic table structure, and calculation methods for mass, moles, and atoms.