1. States of Matter

1.1 The Three States of Matter

Matter is a physical substance that occupies space and has mass. All substances can be categorized as solid, liquid, or gas, which are the three classical states of matter.

• Solids: Particles are packed closely together, vibrating in fixed positions. Strong intermolecular forces hold them in a fixed shape and volume. Solids expand only slightly when heated.

• Liquids: Particles are slightly further apart and can move past each other, allowing liquids to flow and take the shape of their container. Intermolecular forces are weaker than in solids but stronger than in gases. Liquids expand more than solids when heated.

• Gases: Particles are far apart and move freely. Gases have neither fixed shape nor volume and expand to fill their container. Intermolecular forces are very weak.

1.2 Changes of State

Substances can change from one state to another through heating or cooling, which affects the kinetic energy of their particles.

• Melting: Solid to liquid

• Boiling/Evaporation: Liquid to gas

• Condensation: Gas to liquid

• Freezing: Liquid to solid

Heating increases the kinetic energy of particles, allowing them to overcome intermolecular forces and change state. Cooling decreases kinetic energy, allowing intermolecular forces to hold particles in a fixed position.

1.3 Heating and Cooling Curves

Heating and cooling curves show how the temperature of a substance changes as it is heated or cooled. Flat portions of the curve indicate phase changes, where energy is used to break or form intermolecular forces rather than changing temperature.

Example: The heating curve of water shows temperature remaining constant during melting and boiling, as energy is used for the phase change.

1.4 Pressure and Gases

Increasing pressure compresses gas particles, reducing their volume. This is because gas particles are forced closer together, decreasing the space between them.

2. Diffusion

2.1 Diffusion in Matter

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, resulting from their random motion and collisions.

• Occurs in all states of matter but is most rapid in gases due to the large spaces between particles.

• Diffusion equalizes the distribution of particles over time.

2.2 Effect of Relative Molecular Mass on Diffusion

The rate of diffusion of a gas is inversely related to its relative molecular mass (molar mass). Lighter gases diffuse faster than heavier gases.

• Relative molecular mass (Mr): The sum of the atomic masses of the atoms in a molecule.

• Gases with higher Mr diffuse more slowly.

3. Elements, Compounds, and Mixtures

3.1 Elements

Elements are pure substances consisting of only one type of atom. They cannot be broken down into simpler substances by chemical means. Each element has a unique symbol (e.g., H for hydrogen, O for oxygen).

• Classified as metals or non-metals.

• Metals: Usually high melting/boiling points.

• Non-metals: Usually low melting/boiling points.

3.2 Compounds

Compounds are substances formed when two or more different elements are chemically combined in fixed ratios. Their properties differ from those of their constituent elements.

• Can only be separated into elements by chemical reactions.

• Examples: H2SO4, HCl, CO2

3.3 Mixtures

Mixtures are combinations of two or more substances (elements or compounds) not chemically bonded together. They can be separated by physical methods (e.g., filtration, distillation).

• Properties depend on the proportions of constituents.

• Examples: Air, alloys, sea water.

4. Atomic Structure

4.1 Structure of the Atom

Atoms consist of a central nucleus (containing protons and neutrons) surrounded by electrons in shells.

• Protons: Positive charge

• Neutrons: No charge (neutral)

• Electrons: Negative charge

4.2 Atomic Number and Mass Number

• Atomic number (Z): Number of protons in the nucleus. Determines the element.

• Mass number (A): Total number of protons and neutrons in the nucleus.

Example: Carbon has 6 protons and 6 neutrons, so Z = 6, A = 12.

4.3 Electronic Configuration

The electronic configuration describes the arrangement of electrons in shells around the nucleus. The first shell holds up to 2 electrons, the second and third up to 8 each.

• For carbon (Z = 6): 2 electrons in the first shell, 4 in the second. Configuration: 2, 4.

Group VIII elements (noble gases) have full outer shells and are unreactive.

4.4 Isotopes

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same chemical properties because they have the same electronic configuration.

Isotope notation: (A = mass number, Z = atomic number, X = element symbol). Example:

4.5 Calculating Relative Atomic Mass from Isotopes

The relative atomic mass () of an element is calculated from the masses and abundances of its isotopes:

• Relative atomic mass is a weighted average based on natural abundance.

5. Ions and Ionic Bonds

5.1 Ions

Ions are atoms or molecules with a net charge, formed by gaining or losing electrons (not protons). Cations are positively charged (loss of electrons), anions are negatively charged (gain of electrons).

5.2 Ionic Bonds

Ionic bonds are formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other. Typically occurs between metals and non-metals.

• Example: Sodium (Na) loses one electron to become Na+, chlorine (Cl) gains one electron to become Cl-, forming NaCl.

Additional info: This summary covers the fundamental concepts of matter, atomic structure, and chemical substances, providing a strong foundation for further study in General Chemistry.