Compounds, Molecules and Mixtures

• What are the three important terms to understand about atoms?

  Molecules, mixtures, and compounds
• How is a molecule defined?

  A group of two or more atoms bonded together
• Can molecules contain multiple different elements?

  Yes, for example, water molecules
• What is the composition of a water molecule?

  One oxygen and two hydrogen atoms
• Why is helium not considered a molecule?

  It exists as a single atom
• What defines a compound?

  Substances with two or more different elements
• Which of the following is a compound?

  Water
• What is a key feature of compounds regarding element proportions?

  Elements are always in the same proportions
• What is the chemical formula for water?

  H₂O
• What does the subscript in a chemical formula indicate?

  The number of atoms of that element
• What is the formula for carbon dioxide?

  CO₂
• What does the formula H₂SO₄ represent?

  Sulfuric acid
• How do brackets function in chemical formulas?

  They group atoms together for counting
• What does the formula for calcium hydroxide indicate?

  One calcium and two groups of OH
• How can some compounds contain millions of atoms?

  They form large structures with ionic bonds
• What is the formula for sodium chloride?

  NaCl
• Why do ionic bonds lead to large structures?

  They create extensive networks of atoms
• What is a mixture?

  Two or more substances not chemically combined
• How can mixtures be separated?

  Using physical methods like filtration
• Why are there no chemical bonds in mixtures?

  They are physically mixed, not reacted
• What is the purpose of the periodic table in chemistry?

  To look up element symbols and names