Concepts of Chemistry – Exam #2 Study Guide

Classification and States of Matter

Classification of Matter

Matter is anything that has mass and occupies space. It can be classified based on its physical state and composition.

• Physical States: Solid, liquid, and gas, each with distinct properties.

• Pure Substances: Matter with a fixed composition (elements and compounds).

• Mixtures: Physical combinations of two or more substances; can be homogeneous (uniform) or heterogeneous (non-uniform).

Physical changes do not alter the composition of a substance (e.g., melting, boiling), while chemical changes result in the formation of new substances (e.g., burning, rusting).

Properties of Matter:

• Physical Properties: Observed without changing the substance (e.g., color, melting point).

• Chemical Properties: Observed during a chemical change (e.g., flammability, reactivity).

The Atom

Structure of the Atom

Atoms are the basic units of matter, composed of subatomic particles: protons, neutrons, and electrons.

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles found outside the nucleus in electron clouds.

The atomic number is the number of protons in an atom and defines the element. The mass number is the sum of protons and neutrons.

Isotopes are atoms of the same element with different numbers of neutrons.

The Periodic Table

Organization and Trends

The periodic table arranges elements by increasing atomic number and groups elements with similar properties into columns called groups or families.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Periods: Horizontal rows; properties change progressively across a period.

• Main Group Elements: Groups 1, 2, and 13-18.

• Transition Metals: Groups 3-12.

Metals are typically shiny, malleable, and good conductors of heat and electricity. Nonmetals are often gases or brittle solids and poor conductors. Metalloids have properties intermediate between metals and nonmetals.

Compounds and Naming

Types of Compounds

Compounds are substances formed from two or more elements chemically combined in fixed ratios.

• Molecular Compounds: Composed of nonmetals; atoms share electrons (covalent bonds).

• Ionic Compounds: Composed of metals and nonmetals; atoms transfer electrons (ionic bonds).

Naming Compounds

• Ionic Compounds: Name the metal (cation) first, then the nonmetal (anion) with an '-ide' ending. For transition metals, indicate the charge with Roman numerals.

• Molecular Compounds: Use prefixes to indicate the number of each atom (e.g., carbon dioxide, CO2).

Polyatomic ions are charged groups of covalently bonded atoms that act as a unit in compounds (e.g., sulfate SO42-).

Formulas and Charges

Writing Chemical Formulas

Formulas represent the types and numbers of atoms in a compound. For ionic compounds, the total positive and negative charges must balance.

• Example: Sodium chloride: Na+ and Cl- combine to form NaCl.

Roman numerals are used in the names of transition metal compounds to indicate the metal's charge (e.g., iron(III) chloride, FeCl3).

Additional info:

• Students should be able to classify matter, identify physical and chemical changes, and distinguish between elements, compounds, and mixtures.

• Understanding the structure of the atom and the organization of the periodic table is essential for predicting chemical behavior.

• Correctly naming and writing formulas for compounds is a foundational skill in chemistry.