Putting Atoms Together

Learning Goals  I will be able to identify the difference between ionic and covalent compounds.  I will be able to count the number of atoms in compounds and molecules.

Key Terms  Molecule – two or more atoms joined together by a chemical bond €  Chemical formula – tells us the type and number of atoms in a molecule  eg. CaCl 2  Subscript – tells us the number of each atom in a chemical formula  Diatomics – a molecule that is made up of two atoms of the same element. H 2 O 2 F 2 Br 2 I 2 N 2 Cl 2

Why do elements form compounds?  Most elements on their own are not stable. €  To be stable, an element needs 8 electrons in their valence (outer) shell  this is called the octet rule €  So…elements form compounds to get 8 electrons.

Ionic Compounds  Formed by a metal and a nonmetal €  They have ions (charged particles) €  Metals: positively charged (cation); give up/lose electrons €  Nonmetals: negatively charged (anions); take/gain electrons €

Molecular/Covalent Compounds  € Formed by two or more nonmetals €  They share the electrons €

Counting Atoms  Identify as ionic or molecular.  How many of each type of element are present in each compound?  C 2 H 6  CaBr 2  Al 2 O 3  NH 4 (BrO 3 ) 2

Learning Goals Revisited  I will be able to identify the difference between ionic and covalent compounds.  I will be able to count the number of atoms in molecules.

Please Complete …  Counting Atom Worksheet  p261 #2, 3, 5, 6a, 7, 8