Chemistry: Changes and Atomic Structure

Chemical and Physical Changes

• Physical changes alter shape, size, or state of matter, while chemical changes involve a chemical reaction forming new substances.
• Signs of a chemical change include heat, light emission, bubbling, and odor changes.

Solutions and Mixtures

• Solutions are composed of a solvent (dissolving substance) and a solute (dissolved substance).
• Heterogeneous mixtures have visibly distinct components.
• Homogeneous mixtures have uniformly mixed components, making their components indistinguishable.

Atomic Structure

• Subatomic Particles:
  • Protons: Positively charged, located in the nucleus, determine the element.
  • Neutrons: Neutral, located in the nucleus, hold the nucleus together.
  • Electrons: Negatively charged, orbit the nucleus, responsible for bonding.
• Atomic Forces: The four fundamental forces are, in descending order of strength, the Strong Force (nucleus), Weak Force (radioactive decay), Electromagnetic Force (electron orbits), and Gravity (holds atoms together).
• Electron Shells: Energy levels (shells) around the nucleus fill in a specific order: 2, 8, 8, 18, 18, 32, 32.
• Valence Electrons: Electrons in the outermost shell, responsible for chemical bonding.
• Neutral Atoms: Protons equal electrons
• Ions: Atoms with a charge (positive or negative) due to unequal numbers of protons and electrons.
• Isotopes: Atoms of the same element with different numbers of neutrons.
• Atomic Mass: Sum of protons and neutrons.

Atomic History and Discoveries

• Democritus: Theorized the existence of the atom.
• Dalton: Developed atomic theory.
• J.J. Thompson: Discovered electrons.
• Ernest Rutherford: Discovered the atom's mostly empty space structure (gold foil experiment).
• Neils Bohr: Discovered electron shells.
• James Chadwick: Discovered neutrons.
• Schrödinger and Heisenberg: Discovered electron clouds.
• Dmitri Mendeleev: Created the periodic table.

Periodic Table

• Organization: Families/groups (vertical columns) are arranged by similar valence electron numbers, while periods (horizontal rows) indicate the number of electron shells.
• Metals, Nonmetals, Metalloids: A staircase separates metals (left) from nonmetals (right); elements on the staircase are metalloids.
• Atomic Number: The number of protons defines an atom's element and atomic number.

Chemical Bonding

• Ionic Bonds: Transfer of electrons between metals and nonmetals.
• Covalent Bonds: Sharing of electrons between nonmetals.
• Metallic Bonds: A "sea" of electrons shared among metal atoms.
• Valence Electrons: The key to chemical bonding.

Chemical Energy and Reactions

• Stored Chemical Energy: Energy released during a chemical reaction.
• Molecules vs. Compounds: Molecules involve identical atoms bonded, while compounds involve different atoms bonded.
• Lewis Dot Structures: Visual representations of bonding.
• Chemical Reaction Energy Forms: Light, heat, sound, electricity, and mechanical energy can be released during chemical reactions.
• Conservation Laws: The Law of Conservation of Matter (no matter gained/lost during reactions) and the Law of Conservation of Energy (no energy gained/lost).

Acids and Bases

• Acids: Sour taste, formula often starts with "H".
• Bases: Bitter taste, formula often ends with "OH".