AT&T's Version 7 Science Portion: Comprehension of Chemistry

Structure of Atoms

• Atoms are the fundamental building blocks of matter.
• Nucleus contains:
  • Protons (positive charge)
  • Neutrons (no charge)
• Electrons (negative charge) orbit the nucleus.
• Atoms are electrically neutral as protons = electrons.
• Neutrons help stabilize the nucleus by reducing repulsive forces between protons.

Atomic Mass

• Most of an atom's mass is concentrated in the nucleus.
• Protons & Neutrons have similar mass (approx. 1 atomic mass unit each).
• Electrons are much lighter (approx. 0.000549 atomic mass units), often disregarded in mass calculations.

Periodic Table

• Atomic Number: number of protons in an element.
• Atomic Mass: total of protons and neutrons.
• Mnemonic for remembering: PANMAN (Protons-Atomic Number-Neutrons, Mass-Add-Neutrons).

Isotopes

• Atoms of the same element with the same number of protons but different number of neutrons.
• Example: Carbon-12, Carbon-13, Carbon-14.

Ions

• Atoms become ions by gaining or losing electrons:
  • Cations: positively charged (loss of electrons).
  • Anions: negatively charged (gain of electrons).

Shells, Subshells, and Orbitals

• Shells (energy levels): Electrons orbit in fixed paths (denoted by n).
• Subshells: Within shells (s, p, d, f).
• Orbitals: 3D spaces where electrons likely found.
• Shell configuration affects the number of electrons:
  • Shell 1: up to 2 electrons
  • Shell 2: up to 8 electrons
  • Shell 3: up to 18 electrons
  • Shell 4: up to 32 electrons

Chemical Bonds

• Ionic Bonds: Transfer of electrons between atoms.
  • Example: Sodium and Chlorine forming table salt.
• Covalent Bonds: Sharing of electrons between atoms.
  • Example: Carbon dioxide (CO2).

Periods and Groups on the Periodic Table

• Periods: Horizontal rows indicating number of electron shells.
• Groups: Vertical columns with similar chemical properties.

States of Matter

• Solids: Definite shape and volume, incompressible.
• Liquids: Definite volume, indefinite shape, incompressible.
• Gases: Indefinite shape and volume, compressible.

Phase Changes

• Melting: Solid to liquid.
• Freezing: Liquid to solid.
• Condensation: Gas to liquid.
• Evaporation: Liquid to gas.
• Sublimation: Solid to gas.
• Deposition: Gas to solid.

Chemical Reactions

• Involves transformation of reactants to products.
• Types:
  • Synthesis: Combining reactants to form a product.
  • Decomposition: Breaking down a compound.
  • Single Displacement: One element replaces another.
  • Double Displacement: Exchange of components between compounds.
  • Combustion: Burning in oxygen.
• Balance Equations: Ensuring equal number of atoms on both sides.

Moles and Molar Mass

• A mole is 6.022 x 10^23 items (Avogadro's number).
• Molar Mass: Sum of atomic masses in a molecule.

Reaction Rates

• Affected by temperature, concentration, surface area, and catalysts.

Exothermic and Endothermic Reactions

• Exothermic: Releases heat.
• Endothermic: Absorbs heat.

Properties of Water

• Adhesion: Water sticks to other substances.
• Cohesion: Water sticks to itself.
• Solutions: Homogeneous mixtures of solute and solvent.

Osmosis

• Movement of water through a semi-permeable membrane.
• Isotonic: Equal solute concentration.
• Hypertonic: Higher solute concentration.
• Hypotonic: Lower solute concentration.

Diffusion and Active Transport

• Diffusion: Movement from high to low concentration.
• Active Transport: Movement against concentration gradient, requires energy (ATP).

pH Scale

• Ranges from 0 (acidic) to 14 (alkaline), 7 is neutral.
• Acids: Release hydrogen ions in water.
• Bases: Release hydroxide ions in water.
• Neutralization: Acid + Base = Water + Salt.