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Chapter Two

Chapter Two. Chemical Names and Formulas. '. '. * 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:

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Chapter Two

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  1. Chapter Two Chemical Names and Formulas

  2. ' ' *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: CharacteristicMolecular CompoundIonic 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)

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. 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 + -

  8. 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.

  9. 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

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

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

  12. 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

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

  14. 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

  15. 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

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

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