More About Formulas

Formulas Tell the type & number of atoms in a compound. Microscopic level: imagine 1 atom, molecule, or formula unit. Formula gives atom ratios. Macroscopic level: imagine working in the lab Formula gives mole ratio

Formulas Ex: 2H2O can mean 2 molecules of water 2 moles of water. 2H2O molecules have 4 hydrogen atoms & 2 oxygen atoms. 2 Moles of H2O molecules have 4 moles of hydrogen atoms & 2 moles of oxygen atoms.

What can you say about CuSO45H2O? It’s a hydrated salt. For every mole of CuSO4, there are 5 moles of water. If it’s heated, it dries out. The water goes into the air and you’re left with the anhydrous salt, CuSO4. The mole ratio in the formula can be used to predict how much water would be given off by any size sample. If you had 2 moles of CuSO45H2O, how much water would you lose on heating?

Percent Water in CuSO4•5H2O Step 1: Calculate the formula mass. Mass of salt + Mass of water Percent = (Part/Whole) X 100% % H2O = Mass H2O/Formula Mass X 100 %

Ionic vs. Covalent Formulas By looking at the type of atoms, we can decide if the substance is an ionic compound or a molecular (covalent) compound. Molecular compounds have all nonmetals. Ionic compounds usually have metal + nonmetal.

Empirical Formula Smallest whole number ratio of the elements in the compound. Ionic compounds have only empirical formulas. Covalent compounds have empirical and molecular formulas. They can be the same or different.

Molecular Formulas For covalent (molecular) compounds. Give the exact composition of the molecule. Molecular compounds have both empirical and molecular formulas. They can be the same or different.

Say everything you can about: NaCl C6H6 C6H12O6 CH4 CF4 BeSO4 C8H18 KI C2H4Cl2 CaBr2 CuSO45H2O Ionic, empirical Covalent, molecular Covalent, molecular Covalent, empir., molec? Covalent, empirical, molecular? Ionic, empirical Covalent, molecular Ionic, empirical Covalent, molecular Ionic, empirical Ionic, empirical

Say everything you can about PH3 C2H4 Al2O3 SrI2 NF3 H2Se CH3OH SiO2 H2O2 CCl4 XeF4 P4O10

Relationship between empirical and molecular formulas The molecular formula is a whole number multiple of the empirical formula. Molec. Formula = n (Empirical Form.) n is a small whole number, which multiplies the subscripts. Sometimes, n = 1.

Molecular Formula If you know the empirical formula and the molar mass, you can find the molecular formula. Step 1: Find the mass of the empirical formula. Step 2: Molar mass  Empirical mass = small whole number, n Step 3: Multiply the subscripts in the empirical formula by n.

Finding Molecular Formulas Find the molecular formula for the substance whose empirical formula is CH and whose molar mass = 78.0 g Step 1: Empirical mass = 13.0 g Step 2: Molar mass = n = 78.0/13.0 n = 6. Step 3: 6 X subscripts in CH = C6H6. Empirical mass