Asked by lilly

is CO2 a single atom or molecules?
Answered by DrBob222
It's a molecule. It consists of three atoms; i.e., 1 atom of C and 2 atoms of oxygen. A single atom would not have a formula of two elements attached to one another. For example, Na is a single atom. Na2O is a compound.
Answered by sara
thanks:) so why is Rb2O a formula untis and not a molecule?
Answered by DrBob222
Rb2O is an ionic compound and that is the simplest empirical formula for the compound. However, in ionic compounds there is a three-dimensional array of positive and negative ions (Rb^+ and O^-2 ions in this case) so there is no molecule as such. We often call them molecules and we refer to molar mass and molecular weight which is why some profs prefer to call them formula weights or formula masses to indicate that is the mass of the formula and not a molecule. Technically, we should write Na<sub>x</sub>Cl<sub>x</sub> for NaCl because the 3-D array consists of x units of Na^+ and x units of Cl^- and they stretch in three dimensions. The value of x is some number that depends upon how large the formula unit we are viewing happens to be. x is one value for a cube of NaCl 1 cm x 1 cm x 1 cm but some other value for a cube of NaCl that is 1.5 cm x 1.5 cm x 1.5 cm.
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