Meditaliano IMAT Prep

Part 1: The Building Blocks of Matter

1.1 Elements, Atoms, and Compounds

An element is a pure substance made of only one type of atom. An atom is the smallest unit of an element that retains the properties of that element. All atoms are made of three subatomic particles:

• Protons (p⁺): Found in the nucleus, have a positive charge (+1), and a mass of ~1 amu.
• Neutrons (n⁰): Found in the nucleus, have no charge (0), and a mass of ~1 amu.
• Electrons (e⁻): Orbit the nucleus in shells, have a negative charge (-1), and a very small mass.

A compound is a substance formed when atoms of two or more different elements chemically bond together. A molecule is the smallest electrically neutral unit of a substance that still has the properties of the substance. For example, a water molecule ($H_2O$) is the smallest unit of water.

1.2 Chemical Formulas

A chemical formula is a concise way to represent the elements and the number of atoms of each element in a molecule. The element is represented by its symbol, and the number of atoms is written as a subscript after the symbol. If there is only one atom, no subscript is used.

1.3 Ions: Charged Atoms

An ion is an atom or molecule that has gained or lost one or more of its valence electrons, giving it a net electrical charge. Atoms are neutral because they have an equal number of protons (+) and electrons (-). When this balance changes, an ion is formed.

• Cation: A positively charged ion, formed when an atom loses electrons (e.g., $Na^+$).
• Anion: A negatively charged ion, formed when an atom gains electrons (e.g., $Cl^-$).

Part 2: The Periodic Table

2.1 Organization: Groups and Periods

The Periodic Table organizes elements by increasing atomic number. Its structure is not random; it's designed to group elements with similar properties together.

• Periods: The horizontal rows. Elements in the same period have the same number of electron shells.
• Groups (or Families): The vertical columns. Elements in the same group have the same number of valence electrons and thus similar chemical properties.

Key Groups

• Group 1: Alkali Metals (very reactive).
• Group 2: Alkaline Earth Metals.
• Group 17: Halogens (very reactive non-metals).
• Group 18: Noble Gases (very unreactive/inert).

2.2 Periodic Trends

The position of an element on the periodic table can tell us about its properties. These properties change in a predictable way, or trend, across the table.

Part 3: Chemical Bonds & Molecular Shapes

3.1 Chemical Bonds: Holding Atoms Together

Atoms form bonds to achieve a more stable electron configuration, typically by filling their outermost electron shell. The type of bond depends on the electronegativity difference between the atoms.

Ionic Bonds (Transfer of e⁻)

Forms between atoms with a large electronegativity difference (typically metal + non-metal). One atom transfers electrons to another, creating a cation and an anion. The electrostatic attraction between these opposite charges forms the bond. Ex: $NaCl$.

Covalent Bonds (Sharing of e⁻)

Forms between atoms with similar electronegativity (typically non-metal + non-metal).

• Nonpolar Covalent: Equal sharing of electrons (e.g., $O_2, N_2, Cl_2$). Occurs between identical atoms.
• Polar Covalent: Unequal sharing of electrons due to an electronegativity difference. This creates partial positive ($\delta^+$) and partial negative ($\delta^-$) charges on the atoms (e.g., $H_2O, HCl$).

3.2 Molecular Shapes (VSEPR Theory)

The Valence Shell Electron Pair Repulsion (VSEPR) theory states that electron pairs in the valence shell of an atom repel each other. Molecules adopt a 3D shape that minimizes this repulsion, which determines many of their properties.

Part 4: States of Matter and Their Changes

4.1 Solids, Liquids, and Gases

The state of a substance depends on the balance between the kinetic energy of its particles and the strength of its intermolecular forces (IMFs) - the attractions between molecules.

4.2 Phase Changes

Phase changes are physical changes where a substance goes from one state to another. These changes occur at a constant temperature and involve the absorption or release of energy.

4.3 Phase Diagrams

A phase diagram shows the conditions of temperature and pressure at which a substance exists as a solid, liquid, or gas. Key features include the triple point (where all three phases coexist) and the critical point.

Part 5: Chemical Reactions

5.1 Balancing Chemical Equations

The Law of Conservation of Mass states that matter is not created or destroyed. Therefore, a chemical equation must have the same number of atoms of each element on both the reactant and product sides. We use coefficients to balance equations.

5.2 Major Reaction Types

5.3 Oxidation-Reduction (Redox) Reactions

Redox reactions involve the transfer of electrons. These are extremely common and important in biology and chemistry.

• Oxidation: Loss of electrons. The oxidation number increases.
• Reduction: Gain of electrons. The oxidation number decreases.

5.4 Acids and Bases & The pH Scale

Acids and bases are common classes of compounds with distinct properties.

• Acids: Produce $H^+$ ions in water (e.g., $HCl$). pH < 7.
• Bases: Produce $OH^-$ ions in water (e.g., $NaOH$). pH > 7.

Part 6: The Mole Concept & Stoichiometry

6.1 The Mole and Molar Mass

Because atoms are too small to count individually, chemists use a unit called the mole. A mole is simply a counting unit for a very large number of particles. The molar mass is the mass of one mole of a substance (g/mol) and is found on the periodic table.

6.2 Stoichiometry

Stoichiometry is the use of mole ratios from a balanced chemical equation to calculate the amounts of reactants and products. It's the "recipe" of a chemical reaction.

Summary and Practice

This lesson covered the core foundations of chemistry. You should now be familiar with atomic structure, the periodic table, bonding, states of matter, reaction types, and the concept of the mole.

Practice Set (Lesson 0)