Compounds C1

• What are the three important terms to understand when looking at how atoms exist in the real world?

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

  A molecule is a group of two or more atoms held together by chemical bonds.
• What is an example of a molecule found in the air?

  Oxygen
• Can molecules contain multiple different elements? Give an example.

  Yes, for example, water molecules contain one atom of oxygen and two atoms of hydrogen.
• What is the formula for water?

  H₂O
• Why is helium not considered a molecule?

  Because helium exists as a single atom.
• What distinguishes compounds from molecules?

  Compounds contain two or more different elements, while molecules can consist of one or more of the same element.
• What is an example of a compound?

  Water (H₂O)
• What is a key feature of compounds regarding the elements involved?

  The elements in a compound are always found in the same proportions.
• How is the formula for carbon dioxide written?

  CO₂
• What does the subscript in a chemical formula signify?

  The subscript indicates the number of atoms of that element in the molecule.
• What is the formula for sulfuric acid?

  H₂SO₄
• How can you identify the number of atoms in a compound from its formula?

  By reading the subscripts next to each element's symbol.
• What does the presence of brackets in a chemical formula indicate?

  Brackets group together atoms, and the number outside indicates how many of those groups there are.
• What is the formula for calcium hydroxide?

  Ca(OH)₂
• How do ionic bonds affect the structure of compounds?

  Ionic bonds can lead to the formation of large structures rather than small molecules.
• What is the formula for sodium chloride?

  NaCl
• How can you tell the ratio of sodium to chloride in sodium chloride?

  The formula NaCl indicates a one-to-one ratio of sodium to chloride.
• What defines a mixture?

  A mixture consists of two or more substances that are not chemically combined.
• How can you separate the components of a mixture?

  Using physical methods like filtration, crystallization, or distillation.
• What are the differences between molecules, compounds, and mixtures?

  • Molecules: Groups of two or more atoms bonded together.
  • Compounds: Substances containing two or more different elements bonded together.
  • Mixtures: Combinations of two or more substances that are not chemically combined.
• What are the key features of compounds?

  • Contain two or more different elements.
  • Atoms are held together by chemical bonds.
  • Elements are always in the same proportions.
• What are the methods to separate mixtures?

  • Filtration
  • Crystallization
  • Distillation