Chem- Chapter 1

• The periodic table is organized by atomic number, which is the number of protons.
• Atomic mass is calculated based on the relative abundance of different isotopes.
• Elements are arranged into groups (columns) and periods (rows).
• • Q: What is an atom?
  • A: The smallest unit of an element that retains its chemical properties.
• • Q: What are the three subatomic particles of an atom and their charges?

  A:

  • Protons: Positive charge (+1)
  • Neutrons: Neutral charge (0)
  • Electrons: Negative charge (-1)
• • Q: What is the difference between atomic number and mass number?

  A:

  • Atomic number: Number of protons in an atom.
  • Mass number: Sum of protons and neutrons in the nucleus
• • Q: What makes an atom neutral?
  • A: An atom is neutral if it has an equal number of protons and electrons.
• • Q: What is a word equation in chemistry?
  • A: A way to describe a chemical reaction using words. E.g., hydrogen + oxygen → water.
• • Q: What is a symbol equation?
  • A: A chemical equation that uses chemical symbols and formulas. E.g., 2H₂ + O₂ → 2H₂O.
• • Q: Why must chemical equations be balanced?
  • A: To obey the law of conservation of mass: atoms cannot be created or destroyed in a chemical reaction.
• • Q: What is the difference between a mixture and a compound?

  A:

  • Mixture: Two or more substances physically combined (can be separated).
  • Compound: Two or more elements chemically combined (cannot be separated by physical means).
• • Q: What is filtration used for?
  • A: To separate an insoluble solid from a liquid (e.g., sand from water).
• • Q: What is crystallization?
  • A: A process to obtain a pure solid from a solution by evaporating the solvent (e.g., salt from saltwater).
• • Q: How does simple distillation work?
  • A: It separates a solvent from a solution by heating the solution until the solvent evaporates and is then condensed back to a liquid.
• • Q: What is fractional distillation used for?
  • A: It is used to separate liquids with different boiling points, such as separating ethanol from water.
• • Q: What is the principle of paper chromatography?

  A: It separates substances based on their different solubilities in a solvent as they move at different rates along the paper.
• Q: What is the Rf value, and how is it calculated?

  Rf=Distance moved by the solvent front /Distance moved by the substance​ It helps identify substances in chromatography.
• • Q: What did John Dalton propose about atoms?
  • A: Dalton proposed that atoms are tiny, indivisible particles, and each element consists of one type of atom.