Chemical Names and Formulas Chapter Two Chemical Names and Formulas

*Introduction to Chemical Bonding* ' ' *Introduction to Chemical Bonding* Every substance is either an element or a compound A Compound consists of more than one kind of atom A compound is either molecular or ionic in nature Characteristics of Molecular and Ionic Compounds: Characteristic Molecular Compound Ionic Compound Representative Unit Molecule Formula Unit Type of Elements Nonmetallic Metal/Non- metal Physical State Solid, Liquid, Gas Solid Melting Point Low(usually < 300 oC) High(>300 oC)

Molecules and Molecular Compound Molecule- the smallest electrically neutral unit of a substance that still has the same properties of that substance Molecular compound- Atoms of different elements can combine chemically to form compounds Atoms combine to form molecules Compounds are composed of molecules                        

Representing Chemical Compounds Molecular compounds are composed of two or more nonmetals A molecular formula shows the number and kinds of atoms present in a molecule of a compound Ionic Compounds are composed of oppositely charged ions combined in electrically neutral groupings A formula unit gives the lowest whole number ratio of ions in the compound.

Periodic Table Facts The # of the A Group = # of outer electrons That is (1A,2A,3A-8A) OR (IUPAC 1,2,13-18) Elements that: Lose electrons are positive Elements that: Gain electrons are negative Elements are most stable when they have 8 outer electrons—known as the Octet Rule Example: Chlorine has 7 electrons/ gains 1/has a negative 1 oxidation number Cl is in Group 7A

Losing/Gaining Electrons Atoms that have 1, 2 or 3 electrons in their outer levels will tend to lose them in interactions with atoms that have 5, 6 or 7 electrons in their outer levels. Atoms that have 5, 6 or 7 electrons in their outer levels will tend to gain electrons from atoms with 1, 2 or 3 electrons in their outer levels. Atoms that have 4 electrons in the outer most energy level will tend neither to totally lose nor totally gain electrons during interactions.

b Ionic Charges a The charges of the ions of the representative elements can be determined by the position of these elements in the periodic table Most transition metals have more than one common ionic charge A polyatomic ion is a group of atoms that behaves as a unit and has a charge + -

Binary (two-element) ionic compounds are named by writing the name of the cation followed by the name of the anion. When a cation can have more than one ionic charge, a Roman numeral is used in the name. Ternary ionic compounds contain at least one polyatomic ion.

Criss-Cross Method Criss-Cross: write symbols put oxidation # above each symbol criss-cross # (not charge) reduce #’s to get lowest possible ratio do not need to write the # 1

A Group Oxidation # Short-cut 1A 2A 3A 4A 5A 6A 7A +1 +2 +3 +4 -3 -2 -1

EXAMPLES OF IONIC COMPOUNDS: 2 ZnS AlCl3 Ba3N2 CuBr2 Zinc sulfide Aluminum Chloride Barium Nitride Copper (II) bromide

Ternary Ionic Compounds Use the criss-cross method Polyatomic ions are involved… “many atoms” that act together with a single charge “treat” the polyatomic as if it is a single element regarding the criss-cross…you cannot change the subscripts for the polyatomic. You might need to use parentheses when criss-crossing oxidation numbers

Ternary Ionic Compounds Sodium Hydroxide…..NaOH Calcium Nitrite……...Ca(NO2)2 Magnesium Sulfate…..MgSO4 Ammonium Nitrate…..NH4NO3 Calcium Phosphate…..Ca3(PO4)2

Molecular Compounds Binary molecular compounds are composed of two nonmetallic elements. Prefixes are used to show how many atoms of each element are present in a molecule of the compound. DO NOT need to criss-cross for molecular compounds…Reason: prefix given

Summary of Naming and Formula Writing Prefixes Used in Naming Binary Molecular Compounds Prefix # Prefix # Mono 1 Hexa 6 Di 2 Hepta 7 Tri 3 Octa 8 Tetra 4 Nona 9 Penta 5 Deca 10

Examples: 1. OF2 SO3 3. Nitrogen trifluoride 4. Dinitrogen tetroxide Name these binary molecular compounds: 1. OF2 SO3 Write formulas for the following binary molecular 3. Nitrogen trifluoride 4. Dinitrogen tetroxide Answers: oxygen difluoride sulfur trioxide 3. NF3 4. N2O4