Basic Chemistry Quiz

Basic Chemistry

• Elements are the simplest form of matter, indivisible into simpler substances.
• The periodic table lists 120 known elements, each with a unique symbol (e.g., gold = Au).
• Elements are composed of atoms.
• Atoms consist of:
  • Protons: Positively charged, located in the nucleus.
  • Neutrons: No charge, located in the nucleus, similar size to protons.
  • Electrons: Negatively charged, orbit the nucleus.
• Atomic Number: The number above the element symbol, representing the number of protons. In a stable atom, it also equals the number of electrons.
• Atomic Mass: The number below the element symbol, representing the total number of protons and neutrons.
• To find the number of neutrons, subtract the atomic number from the atomic mass.
• Changing the number of electrons changes the charge of an atom (forming an ion), but not the element.
• Changing the number of protons changes the type of element.
• Changing the number of neutrons creates an isotope, which is often unstable and radioactive.
• Compounds are formed by combining two or more elements (e.g., H₂O, CO₂, NaCl).
• Compounds bond through different types:
  • Ionic bonds: One atom donates an electron to another (example: NaCl).
  • Covalent bonds: Atoms share electrons (example: CH₄).
• Molecules are the smallest functional units of compounds (e.g., a single H₂O molecule).
• pH scale measures free hydrogen ions in a solution.
• pH 7 is neutral.
• pH < 7 is acidic.
• pH > 7 is basic (alkaline).
• Each whole number change on the pH scale represents a 10-fold difference in acidity or basicity (e.g., pH 4 is 10 times more acidic than pH 5).