Fundamental Chemistry: Elements, Atoms, Laws, and Bonding

Posted on Apr 18, 2025 in Chemistry

Fundamental Chemistry Concepts

Element: A pure substance that cannot be broken down by either physical or chemical methods.
Compound: A pure substance that can be decomposed into its constituent elements by chemical methods.

Law of Conservation of Mass (Lavoisier): The total mass of reactants equals the total mass of products in a chemical reaction.
Law of Definite Proportions (Proust): When two or more elements combine to form a compound, they always do so in the same fixed ratio by mass.
Law of Multiple Proportions (Dalton): When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.
Gay-Lussac’s Law of Combining Volumes: The volumes of reacting gases and the gaseous products bear a simple whole number relationship to one another, when measured under the same conditions of temperature and pressure.
Avogadro’s Hypothesis: Equal volumes of different gases, at the same temperature and pressure, contain the same number of molecules.

Matter is made up of indivisible and indestructible particles called atoms.
Atoms of the same element are identical in mass and properties; atoms of different elements are different.
Compounds are formed by the combination of atoms of different elements in fixed ratios.

Mole (mol): The amount of substance containing 6.022 x 10²³ elementary entities (atoms, molecules, ions, etc.). This number is known as Avogadro’s number.
Avogadro’s Law: One mole of any gas occupies the same volume as one mole of any other gas under the same conditions of temperature and pressure (STP).
The volume occupied by one mole of any gas at Standard Temperature and Pressure (STP: 0°C and 1 atm) is 22.4 Liters.

Atom: The smallest unit of an element that retains the properties of that element, composed of subatomic particles.
Proton: A positively charged particle found in the atomic nucleus. The number of protons defines the atomic number (Z) and equals the number of electrons in a neutral atom.
Electron: A negatively charged particle found in shells or orbitals outside the atomic nucleus.
Neutron: An uncharged particle found in the atomic nucleus.
Mass Number (A): The total number of protons and neutrons in the nucleus of an atom (A = Z + number of neutrons).
Isotope: Atoms of the same element (same Z) but with different numbers of neutrons (different A).

Plum Pudding Model (Thomson): Proposed the atom as a sphere of positive charge with negatively charged electrons embedded within it.
Nuclear Model (Rutherford): Described the atom as having a dense, positively charged nucleus containing protons (and later neutrons), with electrons orbiting around it.
Bohr Model: Suggested that electrons orbit the nucleus in specific energy levels or shells, and energy is emitted or absorbed when an electron moves between these orbits.

Electromagnetic Wave: A form of energy that travels as a wave at the speed of light, exhibiting both wave-like and particle-like properties.

Periodic Table: Elements are arranged in order of increasing atomic number (Z) into 18 groups (columns) and 7 periods (rows), showing periodic trends in properties.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a stable configuration with eight electrons in their outermost electron shell.
Electron Affinity: The energy change that occurs when an electron is added to a neutral atom in the gaseous state.
Electronegativity: A measure of the tendency of an atom to attract a bonding pair of electrons. Higher electronegativity indicates a stronger attraction. Atoms with low electronegativity are considered electropositive.
Metallic Character: The tendency of an element to lose electrons and form positive ions (cations).
Ionization Energy: The minimum energy required to remove an electron from a neutral atom in the gaseous state.

Ionic Bond: Formed between a metal (loses electrons) and a nonmetal (gains electrons), resulting in an electrostatic attraction between oppositely charged ions, typically forming a crystal lattice. (Characteristics: solid, high melting/boiling points, hard, often water-soluble).
Covalent Bond: Formed between nonmetals sharing electrons to achieve stable electron configurations, resulting in molecules. (Characteristics: lower melting/boiling points, solubility varies, generally poor electrical conductors).
Metallic Bond: Found in metals, where valence electrons are delocalized and shared among a lattice of positive metal ions, forming a ‘sea of electrons’. (Characteristics: metallic luster, ductile, malleable, good electrical/thermal conductors, high melting/boiling points).