Presentation on theme: "Chemical Names and Formulas"— Presentation transcript:
1Chemical Names and Formulas Chapter TwoChemical Names and Formulas
2*Introduction to Chemical Bonding* ''*Introduction to Chemical Bonding*Every substance is either an element or a compoundA Compound consists of more than one kind of atomA compound is either molecular or ionic in natureCharacteristics of Molecular and Ionic Compounds:Characteristic Molecular Compound Ionic CompoundRepresentative Unit Molecule Formula UnitType of Elements Nonmetallic Metal/Non metalPhysical State Solid, Liquid, Gas SolidMelting Point Low(usually < 300 oC) High(>300 oC)
3Molecules and Molecular Compound Molecule- the smallest electrically neutral unit of a substance that still has the same properties of that substanceMolecular compound- Atoms of different elements can combine chemically to form compoundsAtoms combine to form moleculesCompounds are composed of molecules
4Representing Chemical Compounds Molecular compounds are composed of two or more nonmetalsA molecular formula shows the number and kinds of atoms present in a molecule of a compoundIonic Compounds are composed of oppositely charged ions combined in electrically neutral groupingsA formula unit gives the lowest wholenumber ratio of ions in the compound.
5Periodic 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 positiveElements that: Gain electrons are negativeElements are most stable when they have 8 outer electrons—known as the Octet RuleExample: Chlorine has 7 electrons/ gains 1/has a negative 1 oxidation number Cl is in Group 7A
6Losing/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.
7b Ionic Charges aThe charges of the ions of the representative elements can be determined by the position of these elements in the periodic tableMost transition metals have more than one common ionic chargeA polyatomic ion is a group of atoms that behaves as a unit and has a charge
8Binary (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.
9Criss-Cross Method Criss-Cross: write symbols put oxidation # above each symbolcriss-cross # (not charge)reduce #’s to get lowest possible ratiodo not need to write the # 1
11EXAMPLES OF IONIC COMPOUNDS: 2ZnSAlCl3Ba3N2CuBr2Zinc sulfideAluminum ChlorideBarium NitrideCopper (II) bromide
12Ternary Ionic Compounds Use the criss-cross methodPolyatomic 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
14Molecular CompoundsBinary 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
15Summary of Naming and Formula Writing Prefixes Used in Naming Binary Molecular CompoundsPrefix # Prefix #Mono 1 HexaDi 2 HeptaTri 3 OctaTetra 4 NonaPenta 5 Deca
16Examples: 1. OF2 SO3 3. Nitrogen trifluoride 4. Dinitrogen tetroxide Name these binary molecularcompounds:1. OF2SO3Write formulas for thefollowing binary molecular3. Nitrogen trifluoride4. Dinitrogen tetroxideAnswers:oxygen difluoridesulfur trioxide3. NF34. N2O4