8th Grade Science Study Guide Flashcards

Atoms & the Periodic Table

  • Atom: The smallest unit of matter.
  • Electron: Negatively charged particle that orbits the nucleus.
  • Nucleus: Center of an atom; contains protons and neutrons.
  • Proton: Positively charged particle in the nucleus.
  • Neutron: Neutral particle in the nucleus.
  • Atomic number: Number of protons in an atom.
  • Isotope: Atoms of the same element with different numbers of neutrons.
  • Mass number: Sum of protons and neutrons.
  • Atomic mass: Average mass of all isotopes of an element.
  • Periodic table: Chart that organizes elements by atomic number.
  • Chemical symbol: One- or two-letter abbreviation for an element.
  • Period: Horizontal row on the periodic table.
  • Group: Vertical column on the periodic table; elements share properties.

Chemical Bonds & Reactions

  • Compound: Substance made of two or more elements chemically bonded.
  • Valence electron: Electrons in the outer shell; involved in bonding.
  • Reactivity: How easily an element reacts with others.
  • Ion: Atom that has lost or gained electrons.
  • Polyatomic ion: A group of atoms that act as a single ion.
  • Ionic bond: Transfer of electrons between atoms (usually metal + nonmetal).
  • Covalent bond: Sharing of electrons between atoms (usually nonmetals).
  • Molecule: Group of atoms bonded covalently.
  • Nonpolar bond: Electrons shared equally.
  • Polar bond: Electrons shared unequally.

Properties of Materials

  • Malleable: Can be hammered into shapes.
  • Ductile: Can be drawn into wires.
  • Luster: How shiny a material is.
  • Semiconductor: Material that conducts electricity under certain conditions.

Acids, Bases, and Solutions

  • Acid: Substance that produces hydrogen ions (H+)(H^+); pH < 7.
  • Corrosive: Ability to wear away other materials (like metals).
  • Indicator: Substance that changes color in acids or bases.
  • Base: Produces hydroxide ions (OH−)(OH^-); pH > 7.
  • Neutralization: Reaction between an acid and a base.
  • Salt: Product of neutralization (besides water).
  • Mixture: Two or more substances not chemically bonded.
  • Colloid: Mixture with small undissolved particles.
  • Suspension: Mixture with large particles that settle out.
  • Solution: Homogeneous mixture where one substance dissolves in another.
  • Solvent: Substance that does the dissolving (usually water).
  • Solute: Substance being dissolved.
  • Solubility: How much solute can dissolve in a solvent at a given temp.

Changes in Matter

  • Physical change: Change in appearance, not chemical makeup.
  • Chemical change: New substances are formed with different properties.
  • Reactant: Starting substances in a reaction.
  • Product: New substances formed.
  • Exothermic reaction: Releases heat.
  • Endothermic reaction: Absorbs heat.
  • Law of conservation of mass: Matter is not created or destroyed.
  • Open system: Matter can enter/exit the system.
  • Closed system: No matter enters or leaves.

Materials & Resources

  • Synthetic: Made by humans in a lab.
  • Natural resource: Found in nature, not man-made.
  • Polymer: Large molecule made of repeating units (natural or synthetic).

Motion & Forces

  • Motion: Change in position over time.
  • Reference point: Place used to determine motion.
  • Force: A push or pull.
  • Newton: SI unit for force.
  • Friction: Resistance between surfaces.
  • Gravity: Force that pulls objects toward each other.
  • Net force: Total force acting on an object.
  • Speed: Distance traveled over time.
  • Slope: Steepness of a line (used in speed graphs).
  • Velocity: Speed with direction.
  • Acceleration: Change in velocity over time.
  • Inertia: Resistance to change in motion.
  • Weight: Force of gravity on an object.

Genetics & Heredity

  • Heredity: Passing of traits from parents to offspring.
  • Dominant allele: Trait that shows up when present.
  • Recessive allele: Trait that only shows up when two copies are present.
  • Probability: Likelihood of a genetic outcome.
  • Genotype: Genetic makeup (e.g., Bb, BB).
  • Phenotype: Physical appearance (e.g., brown eyes).
  • Chromosome: Structure in cells that contains DNA.
  • Cell cycle: Process of cell growth and division.
  • Pedigree: Chart showing genetic relationships in a family.
  • Meiosis: Cell division that produces sex cells (gametes).
  • Chromatids: Identical halves of a duplicated chromosome.
  • Mitosis: Cell division that produces body cells.

DNA & Genetic Engineering

  • DNA: Genetic material that holds instructions for life.
  • Protein synthesis: Process of making proteins from DNA instructions.
  • Messenger RNA (mRNA): Carries DNA code to ribosome.
  • Transfer RNA (tRNA): Brings amino acids to ribosome.
  • Variation: Differences between individuals.
  • Sex chromosomes: Determine gender (X and Y).
  • Autosomal chromosomes: All other chromosomes not related to gender.