History of the Atom and Its Properties

History of the Atom

• Democritus proposed the idea of atoms as indivisible particles, differing in shape and size.
• John Dalton developed the first modern atomic theory, stating that elements are composed of unique atoms, which are indivisible, indestructible, and identical in mass and properties.
• J.J. Thomson discovered the electron using cathode ray tubes, leading to the "plum pudding" model where electrons were scattered in a positively charged sphere.
• Ernest Rutherford's gold foil experiment led to the discovery of the nucleus, resulting in the nuclear model.
• Niels Bohr introduced the Bohr model, proposing that electrons orbit the nucleus in specific energy levels and can move between them by absorbing or emitting energy.

Physical and Chemical Properties

• Physical properties can be observed without changing the substance's chemical composition. Examples include color, melting point, density, and solubility.
• Chemical properties describe a substance’s behavior when it undergoes a change to form a new substance. Examples include reactivity with acids, flammability, and oxidation states.

Physical and Chemical Changes

• Physical changes alter the form or state of a substance, but not its chemical composition. Examples include melting ice, tearing paper, and making a mixture.
• Chemical changes alter the chemical composition of a substance, creating new substances. Examples include burning paper, digesting food, and iron reacting with oxygen gas.

Groups and Periods on the Periodic Table

• Alkali metals (Group 1) are highly reactive, especially with water. Examples include lithium, sodium, and potassium.
• Alkaline earth metals (Group 2) are also reactive, but less so than alkali metals. Examples include beryllium, magnesium, and calcium.
• Halogens (Group 17) are highly reactive nonmetals. Examples include fluorine, chlorine, and bromine.
• Noble gases (Group 18) are inert due to their full valence shells. Examples include helium, neon, and argon.
• Transition metals (Groups 3-12) often form colourful compounds and are good conductors. Examples include iron, copper, and gold.
• Metalloids (Groups 13-16, excluding boron) have properties between metals & nonmetals. Examples include silicon, germanium, and arsenic.
• Nonmetals (Groups 14-17, excluding noble gases) are typically dull, brittle, and non-conductive. Examples include carbon, nitrogen, and oxygen.

Ions and Isotopes

• Ions are atoms that have gained or lost electrons, resulting in a net electrical charge. Cations are positively charged, while anions are negatively charged.
• Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses.

Atoms, Molecules, and Compounds

• Atoms are the basic units of matter, consisting of protons, neutrons, and electrons.
• Molecules consist of two or more atoms bonded together, which can be the same or different elements.
• Compounds are substances formed when two or more different elements chemically bond.

Bohr-Rutherford Diagram

• The nucleus is at the center of the atom, containing protons (positive charge) and neutrons (neutral charge).
• Electrons orbit the nucleus in specific energy levels called shells.
• The Bohr-Rutherford diagram depicts the atom with the nucleus at the center and circles representing electron shells, with dots or small circles representing electrons in their shells.

HHPS Safety

• The diagram illustrates safety symbols and procedures for a chemistry laboratory.

Definitions

• Physical Properties: Characteristics observable without changing the substance's chemical composition. Examples include color, density, and solubility.
• Chemical Properties: Characteristics that describe how a substance behaves when undergoing a chemical change. Examples include flammability, reactivity, and oxidation states.
• Physical Changes: Changes that alter the form or state of a substance but not its chemical composition. Examples include melting ice, tearing paper, and making a mixture.
• Chemical Changes: Changes that alter the chemical composition of a substance, creating new products. Examples include burning paper, digesting food, and iron reacting with oxygen.
• State of Matter: Describes the behavior of atoms and molecules in a substance, including solid, liquid, and gas.
• Flammability: The ability of a substance to burn and light on fire.
• Reactivity: The tendency of a substance to undergo chemical reactions.
• Decomposition: The process of rotting or decaying.
• Combustion: A chemical process involving rapid reaction with oxygen, releasing heat and light. Example: Burning wood or petrol.
• Combustibility: The ability of a substance to burn.
• Corrosion: The degradation of a metal due to a reaction with its environment. Examples include rusting of iron and tarnishing of silver.
• Ductility: The ability of a substance to be drawn into a wire.
• Texture: The feel, appearance, or consistency of a substance.
• Luster: The shine or gloss of a substance.
• Odor: A distinctive smell.
• Inert: Lacking the ability to react or move.
• Malleability: The ability of a substance to be shaped without breaking.
• Conductivity: The ability of a substance to conduct heat or electricity.
• Density: The ratio of mass to volume.
• Solubility: The degree to which a substance dissolves in a solvent.
• Viscosity: The resistance of a fluid to flow.