Hey future chemists! Grab your lab goggles and let's dive into some electrifying (pun intended) concepts: Relative Molecular Mass, Molar Mass, and how they come together in the exciting world of chemistry.

• What is it? The ratio of the mass of an atom to one-twelfth of the mass of a carbon-12 atom.
• Unit? Nope, it's a ratio, so no units here!
• Real-world example: Think of it like comparing the weight of a watermelon to a piece of fruit that's 12 times heavier. The Ar is the watermelon's weight portion.

• What is it? Just like Ar, but for a molecule or multiatomic species.
• How to calculate? Add together the Ar values for all atoms in the molecule. Easy peasy!
• Real-world example: Imagine building a LEGO structure (molecule), and each brick (atom) has its weight (Ar). The total weight of the structure is the Mr.

• For ionic substances, we use the smallest formula unit.
• Example: For calcium chloride (CaCl2), Mr (CaCl2) = Ar (Ca) + 2 × Ar (Cl) = 40.08 + (2 × 35.45) = 110.98.
• Cool Fact: Ions weigh about the same as neutral atoms because electron masses don't really count here!