Chemistry Chapter 1: Substances and Changes

Pure Substances and Mixtures

• Pure substances are composed of only one type of particle.
• Elements (e.g., oxygen, O₂) and compounds (e.g., water, H₂O) are pure substances.
• Mixtures are made of two or more substances physically combined.
• Homogeneous mixtures (solutions) appear uniform throughout (e.g., saltwater).
• Heterogeneous mixtures have visible different parts (e.g., salad).

Physical and Chemical Properties

• Physical properties can be observed without changing the substance (e.g., color, density, melting point).
• Chemical properties describe how a substance reacts with other substances (e.g., flammability, reactivity with acid).

Physical vs. Chemical Changes

• Physical changes do not create new substances. They alter form or state (e.g., melting ice, cutting paper).
• Chemical changes create new substances with different properties (e.g., burning wood, rusting iron).
  • Clues include color change, gas production, or temperature change.

Kinetic Molecular Theory (KMT)

• All matter is composed of tiny particles in constant motion.
• Particles are always in motion.
• Higher temperatures lead to faster particle movement.
• Solids, liquids, and gases have different particle arrangements.

Changes of States of Matter

• Melting: Solid to liquid (heat added).
• Freezing: Liquid to solid (heat removed).
• Evaporation: Liquid to gas (heat added).
• Condensation: Gas to liquid (heat removed).
• Sublimation: Solid directly to gas (e.g., dry ice).
• Deposition: Gas directly to solid (e.g., frost).

Separating Mixtures

• Filtration separates solids from liquids (e.g., coffee filter).
• Evaporation removes a liquid to leave a solid behind (e.g., salt from seawater).
• Distillation separates liquids based on boiling points.
• Magnetism separates magnetic materials (e.g., iron filings from sand).

Diffusion

• Particles move from high concentration to low concentration.
• Diffusion is faster in gases than in liquids.
• Example: Smelling perfume from across the room.

History of an Atom

• Democritus (400 BCE) proposed the idea of indivisible particles ("atomos").
• John Dalton (1803) proposed a theory of atoms as tiny, solid spheres.
• J.J. Thomson (1897) discovered the electron, leading to the plum pudding model, using the cathode ray tube.
• Ernest Rutherford (1911) discovered the nucleus through the gold foil experiment.
• Niels Bohr (1913) proposed electrons orbit the nucleus in fixed paths.
• The modern (quantum mechanical) model describes electrons as existing in electron clouds.

Atomic Theory and Subatomic Particles

• Atomic theory states all matter is made of atoms.
• Atoms are composed of protons, neutrons, and electrons.
  • Protons (+), in the nucleus, have a positive charge.
  • Neutrons (0), in the nucleus, have no charge.
  • Electrons (-), in electron clouds, have a negative charge.
• Atomic number equals the number of protons.
• Mass number equals protons + neutrons.