Science Class 9
Atomic Foundations of Matter
Weigh a chemical change, compare atoms in u, and write any formula.
11 lessons · ~60 min total
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Lessons in this topic
- 0 Start here A roadmap: two weighings, one idea, and a short rule for writing formulas. · 3 min You are here
- 1 Nothing is lost In a closed system, mass before a change equals mass after. · 6 min
- 2 Always the same proportion A compound's elements are always in the same mass ratio. · 6 min
- 3 Why those two hold One idea about atoms explains why mass holds and ratios stay fixed. · 6 min
- 4 Weighing something you cannot see Atomic mass compares each atom to a carbon-12 atom, fixed at 12 u. · 6 min
- 5 Molecular mass Add a formula's atomic masses to get molecular or formula-unit mass. · 6 min
- 6 When it is not molecules Some substances are ions in a repeating ratio, not molecules. · 6 min
- 7 Valency Each element here has one usual combining number, called its valency. · 6 min
- 8 Writing the formula Swap two valencies, cut them down, and write the formula. · 6 min
- 9 The big picture The whole chapter on one screen. · 3 min
- 10 Track quiz Eight quick questions, one for each idea. · 6 min
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