WRITING AND NAMING CHEMICAL FORMULAS

STANDARDS Predict chemical formulas based on the number of valence electrons and oxidation numbers Name and write the chemical formulas for simple ionic and molecular compounds, including common polyatomic ions. (standard list of common polyatomic ions need to be memorized)

Terms Element Compound

ELEMENTS Elements are composed of only one type of atom Periodic Table is a listing of all the known elements Handout

ATOMS The smallest part of an element that has all the properties of that element Building blocks of the universe –Everything in the universe is made up of atoms Scanning tunneling microscope

PARTS OF AN ATOM Protons Neutrons electrons

ROLE OF PROTONS, NEUTRONS, AND ELECTRONS

ISOTOPES Atoms of the same element that differ in their number of neutrons In nature, most elements are found as a mixture of isotopes Examples

Atomic mass Also called atomic mass units AMU It is the relative mass of an atom and its common isotopes compared to carbon Carbon is the standard Location

Mass number It is the atomic mass rounded to the nearest whole number It is equal to the sum of the protons and neutrons in that atom Used to determine the number of neutrons

Calculating average atomic mass Not all isotopes of an element will be present in the same amount.

SAMPLE PROBLEM Neon has 2 isotopes. Neon- 20 has a mass of u and neon – 22 has a mass of u. In an average sample of 100 atoms, 90 will be neon 20 and 10 will be neon –22. Calculate the average atomic mass.

SAMPLE PROBLEM Two isotopes of the same element have the following: 1 st isotope u 7.5% abundance 2 nd isotope u 92.5% Calculate the atomic mass of the unknown element and determine the elements identify.

Properties of compounds Properties of compounds are different from those of the elements that make up the compound

Chemical formula Combination of symbols that represent the composition of a compound. Formula represents –elements involved –ratio of those elements

Structural formula Shows how atoms are joined Shows kind of atoms and the number of atoms used primarily with organic compounds example

Interpreting chemical formulas practice

Writing chemical formulas Monatomic ions polyatomic ions oxidation number periodic table handout - memorize roman numeral silver Older naming system practice

Naming chemical formulas Handout - memorize chart transition elements

Molecular formula Formulas for compounds that exist as molecules

Empirical formula The simplest formula used to help identify unknown substances Molecular formula of a compound is always written as some whole-number multiple of the empirical formula ionic compounds - always written as empirical formula

Writing empirical formula Practice problems

Law of definite proportion A compound is always composed of the same elements in the same proportions by mass The mass of the compound is equal to the sum of the masses of the element that make up the compound

Percent by mass formula Mass of element x100 Mass of compound

Sample Problem

Law of Multiple Proportions When different compounds are formed by a combination of the same elements, different masses of one element element combine with the same relative mass of the other element in a ratio of small whole numbers.