Early wheels were simple wooden disks with a hole for the axle. In the early Roman empire, most horse-carts used a design featuring two chords across the wheel. The spoked wheel was invented much more recently, and allowed the construction of lighter and swifter vehicles.
Chromium(III) sulfide. Chromium(III) Sulfide is the inorganic compound with the formula Cr2S3. It is a brown-black solid. Chromium sulfides are usually nonstoichiometric compounds, with formulas ranging from CrS to Cr0.67S (corresponding to Cr2S3). Preparation.
A chemical formula is a concise list of the elements in a compound and the ratios of these elements. To better understand what a chemical formula means, we must consider how an ionic compound is constructed from its ions.alcium ions have a charge of 2+, while nitrate ions have a charge of 1â. We will need two nitrate ions to balance the charge on each calcium ion. The formula for nitrate must be enclosed in parentheses. Thus, we write Ca(NO3)2 as the formula for this ionic compound.