Formulas and equations sim
Formula: an ionic compound has no overall charge.
Formulas and equations · covers the GCSE, IGCSE, O-Level topic
What the sim shows
Formula: an ionic compound has no overall charge. Write each valency (the size of the charge, no sign) above its ion and cross the numbers down as subscripts; bracket a polyatomic ion whose number is more than 1; divide by any common factor; a 1 is never written. Equal valencies give 1 to 1. Valency: groups 1, 2 and 13 give 1, 2 and 3, groups 14 to 17 give 18 minus the group number, and group 18 gives 0; a Roman numeral is the valency of a metal that can vary. Balance: atoms are neither made nor destroyed, so change only the numbers in front until every element counts the same on both sides, in the lowest whole numbers; an ion that comes through unchanged may be counted as one unit. Ionic equations: only ionic compounds marked (aq), strong acids included, split into ions; an ion the same in form and amount on both sides is a spectator and is crossed out; check atoms and total charge. Half equations: oxidation is loss, so the electrons go on the right; reduction is gain, so they go on the left; each electron counts 1−; scale both halves to the same number of electrons, add, and cancel them. Solubility rules from the lessons: sodium, potassium and ammonium salts and all nitrates dissolve; chlorides, bromides and iodides dissolve except silver and lead(II); sulfates dissolve except barium and lead(II); carbonates and hydroxides do not, except sodium, potassium and ammonium.
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