Chemical Formulas & Mass Foothill Chemistry Chemical Formulas & Mass

Chemical Formulas Review Chemical Formula - Indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. Molecular Formula – Chemical formula for a covalent compound Formula Unit – Chemical formula for an ionic compound

Chemical Formulas Review Lewis Structure – Chemical formula that shows bonding between elements and the unpaired electrons Structural formula – Like a Lewis structure, but no unpaired electrons (and sometimes no hydrogen) – But really a Lewis structure is a type of structural formula Empirical Formula – Shows the composition of a compound in terms of the simplest ratio of atoms (subscripts are a reduced fraction)

Oxidation Numbers / Oxidation States Indicate the general distribution of electrons among the bonded atoms in a molecular compound or polyatomic ion Oxidation numbers are useful in naming compounds, writing formulas, and balancing chemical equations.

Oxidation Number Rules Atoms of a pure elements have an oxidation number of zero. The more electronegative element in a binary compound is assigned as the anion, the less electronegative element is assigned as the cation. Fluorine always has an oxidation number of negative 1 (-1) in compounds.

Oxidation Number Rules Oxygen almost always has an oxidation number of -2, except in peroxides when it has an oxidation number of -1. With fluorine it will have a +2 charge (OF2) Hydrogen has a +1 oxidation number with compounds containing elements that are more electronegative than it is. It has an oxidation number of -1 in combination with metals.

Oxidation Number Rules The algebraic sum of all oxidation numbers in a neutral compound is zero. The algebraic sum of all oxidation numbers in an ionic compound is the charge of the ion. In ionic compounds, the ions have oxidation numbers equal to the charge of the ion.

Oxidation Number Practice UF6 H2SO4 ClO3-

Formula Mass The sum of the average atomic masses of all atoms represented in its formula Formula mass is a general term used for molecules, formula units, and ions. Molecular mass is used for molecules and polyatomic ions. Units are in amu

Molar Mass Mass of one mole of a substance. Numerically equivalent to the formula mass. Units are g/mol Oh no! Moles are back!

Formula Mass / Molar Mass Practice H2SO4 Ca(NO3)2 PO43- MgCl2 Al2S3

Percent Composition Mass of element in sample / mass of sample x 100% Mass of element in 1 mol / m0lar mass x 100% The percentage by mass of each element in a compound is known as the Percent Composition of the compound.

Determining Empirical Formula From Percent Composition Find the number of moles of each element in the compound. Divide each number by the smallest number of moles The smallest whole number ratio is the empirical formula

Empirical Formula Practice (Together) 32.38% sodium, 22.65% sulfur, 44.99% oxygen – What is empirical formula? Sample Mass 10.150g; Phosphorus mass 4.433g; only contains phosphorus and oxygen – What is empirical formula?

In Class Assignment – Due Today Determine the Empirical Formula for the Following: 75% Carbon, 25% Hydrogen 52.7% Potassium , 43% Chlorine 22.1% Aluminum, 25.4% Phosphorus, 52.5% Oxygen 13% Magnesium, 87% Bromine 32.4% Sodium, 22.5% Sulfur, 45.1% Oxygen