Tobin Science — Naming Binary Compounds
Two-element compounds only: ionic and covalent. Built for High School Physical Science.
Start here: what is it made of?
Click a branch. The chart fills in the rule and works an example for you.
What is it made of?Look at the two elements in the formula and find them on the periodic table.
IONIC COMPOUND
COVALENT COMPOUND
What about three or more elements? Those are polyatomic compounds — sodium nitrate, calcium sulfate, that whole family. They use a chart of polyatomic ions and they are not part of this course. If you count three different element symbols in a formula, it is not one of ours. Everything on this page is a binary compound: exactly two elements.
Compound namer — type anything
Type a formula and get the name, or type a name and get the formula. Either way it shows you every step it took, the same steps the chart asks you for.
Why the criss-cross method works
Most students learn to swap the numbers without ever being told why. Step through it once and it stops being a trick.
Try it with
+
Watch the electrons move
The subscripts in an ionic formula are not a rule someone invented. They are the only numbers that make every electron given away land on an atom that wants it. Nothing left over on either side.
+
Why covalent compounds need prefixes at all
Two metals-and-nonmetals only ever combine one way, because the charges have to cancel. Two nonmetals share electrons instead, and they can share in more than one arrangement. So the name has to carry the count — otherwise these two compounds would have the same name and one of them will kill you.
Compare that to ionic. There is only one magnesium chloride, and it is MgCl2. Magnesium is always 2+, chlorine is always 1−, so the formula has no choice. That is exactly why ionic names never use prefixes — the name does not need to carry a count, because the charges already fix it.
The seven diatomic elements
These seven never appear alone. Left by themselves they pair up with a twin. That is what diatomic means — two atoms of the same element. It does not mean a two-element compound, which is what everything else on this page is.
Memory trick: Br I N Cl H O F — "Brinklehof." Or find them on the periodic table: they make a 7 shape, starting at hydrogen and running down the halogen column.
Careful: O2 is oxygen gas, an element. CO2 is carbon dioxide, a compound. A subscript alone does not make something a compound — two different symbols do.
Sign in to practice
First and last name — this is how your teacher gives you credit.
Which set?
Greek prefix flash cards
Click the card to flip it. These are the ten prefixes covalent naming runs on — you have to know them cold or nothing else works.
click to flip
click to flip back
The four rules, in order
Greek prefixes
Charges you can read straight off the periodic table
Group number tells you the charge for every main-group element. No memorizing.
Transition metals — which ones need a Roman numeral
A Roman numeral is not decoration. It tells the reader which charge this metal is using this time. Four metals in the middle block never change, so they never take one.
The −ide endings
The mistakes that cost the most points
Printable sheets
Black and white, no color ink needed. Each one opens your printer dialog — choose Save as PDF if you would rather keep a copy. Answer keys print as their own page, so print the student copy for them and the key for you.
Assign a practice set
Pick a set and share the link. Students sign in with name + period, answer 12 questions built from their own name, and hand you a code. Multiple choice only earns its point if the first answer is right.
Grade assignment codes
Paste every student code below — one big mess is fine. You get a roster sorted by period, then last name.
Check one practice code
For free-practice codes (NCE-…) students earn outside an assignment.
Codes carry the student's name, set, score, and the date, so they cannot be swapped between students. Nothing is uploaded — everything runs on the device, and the page works with the wifi off.
Standards this covers
SPS2 — Explore the nature of matter, its classifications, and its system for naming types of matter. Predict formulas for stable ionic compounds based on charge, and use IUPAC nomenclature for both chemical names and formulas of ionic compounds and binary covalent compounds.
SPS1 — Valence electrons and position on the periodic table are what this page uses to get every charge, so it doubles as trend and electron-arrangement review.
Deliberately left out: polyatomic ions, acids, and hydrates. Binary compounds only, ionic and covalent.