Study Notes on Elements, Compounds, and Mixtures

Atomic Data and Constants

• Avogadro constant ($L$): $6.02 \times 10^{23}\,mol^{-1}$.

• Molar Volume of Gas: The volume of one mole of any gas is $24\,dm^3$ at room temperature and pressure (r.t.p.).

• Periodic Table Arrangement: Elements are organized by increasing proton (atomic) numbers.

Elements

• Definition: Pure substances that cannot be broken down into simpler substances by chemical methods.

• Notation: The first letter of an element's symbol is capitalized; subsequent letters are lowercase.

• Metallic Properties: Characterized by high melting points, good electrical conductivity, and being sonorous, malleable, and ductile.

• Non-metallic Properties: Characterized by low melting/boiling points, brittle texture, and poor electrical conductivity.

• Metalloids: Elements with properties intermediate between metals and non-metals.

Compounds

• Definition: Pure substances composed of two or more elements chemically combined in a fixed ratio.

• Key Characteristics:     * Possess different properties from their constituent elements.     * Fixed melting and boiling points.     * Can only be broken down into simpler substances using chemical methods.

• Formation: Occurs via chemical reactions, involving an exchange of energy with the environment.

Mixtures

• Definition: Two or more substances (elements or compounds) that are not chemically combined.

• Key Characteristics:     * Impure substances that retain the properties of their constituent components.     * Components are not present in fixed proportions.     * Melt and boil over a range of temperatures rather than at fixed points.

• Separation: Can be separated into pure substances using physical methods.