All elements what to be STABLE (full or empty like the noble gases of group 18.) All except H and He want 8 valence electrons (Stable Octet!

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1 SCIENCE FOUNDATIONS Chemical Bonds Remember from last chapter the number of VALENCE ELECTRONS (electrons in the outermost energy level) and OXIDATION NUMBER (ion each element becomes to get full or empty) for each GROUP on the periodic table! All elements what to be STABLE (full or empty like the noble gases of group 18.) All except H and He want 8 valence electrons (Stable Octet!) Elements will GAIN, LOSE or SHARE valence electrons to get STABLE. 1

2 Click to watch the video on Bonding! A58B 4ABF A81E 523B37F43CC7&blnFromSearch=1&productcode=US 2

3 Group # Oxidation # (ion) Valence Electrons 3

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5 Chemical Bond = force that holds atoms or ions together as a unit. 1) IONIC BOND = force that hold cation (positive ion) and anion (negative ion) together. It is formed when atoms TRANSFER electrons. CATION= Positive ion formed when atom LOST electron. IONIC radius is smaller than ATOMIC radius. ANION = Negative ion formed when atom GAINS electron. IONIC radius is BIGGER than ATOMIC radius. 5

6 IONIZATION energy = the amount of energy needed to REMOVE an electron from an atom. (The MORE ionization energy there is the HARDER it is to remove & vv.) *Ionization energy INCREASES as you move RIGHT and UP on the periodic table. (He has the greatest ionization energy, Fr has least!) 6

7 ELECTRON DOT MODEL EACH DOT around the symbol represents a VALENCE electron. Complete the electron dot model for the following: Li Be N O F Ne 7

8 Construct your own electron dot diagram Choose one element & drag the correct number of VALENCE electrons around it. Br ELECTRONS Ca Li S O H N C Cl P Na Mg 8

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10 Shortcut to WRITING IONIC COMPOUNDS: 1) Write the symbol for the CATION (+ ion) first on the left & ANION ( ion) second on the right. 2) Write their OXIDATION NUMBERS (memorized from periodic table location) SUPERSCRIPTED upper right for each. 3) CRISS CROSS the OXIDATION NUMBERS (WITHOUT CHARGES + ) and write them as SUBSCRIPTS in your Chemical Formula. * The number 1 is never written as a subscript. * SIMPLIFY (reduce) IONIC formulas if you can. * Always use WHOLE numbers WITHOUT charges as SUBSCRIPTS. 10

11 Draw the electron dot diagrams for each and figure out how they will combine to form an ionic compound: Mg Cl Pull 11

12 Al S Ca O 12

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14 4) Treat POLYATOMIC IONS just like any other ion, just put PARENTHESIS around the polyatomic ion THEN criss cross and put the subscript OUSTIDE the parenthesis. * Polyatomic ion= covalently bonded group of atoms that have a positive or negative charge & act as a unit like any other ion! Mg PO 4 Ca Cr 2 O 7 NH 4 CO 3 14

15 NAMING IONIC COMPOUNDS: 1 Write the CATION (+ first ion) AS IS on periodic table or polyatomic ion list. 2 Change the ANION ( second ion) ENDING to IDE. Except polyatomic ions whose names NEVER change! NaCl Ca 3 N 2 (NH 4 ) 2 CO 3 15

16 3 IF the cation (+ first element) is a transition metal that can have MULTIPLE oxidation numbers/ions: * Figure out its OXIDATION number in the particular compound by doing the criss cross backwards, but be sure to double check the anion s oxidation number to be sure it was not reduced! * Write its OXIDATION number as a ROMAN NUMERAL after it in the name. Fe 2 O 3 FeO 16

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18 Practice Writing the following Ionic Compounds Use the pull tab to get the oxidation numbers for each group. Pull Al CO 3 Ba S NH 4 N 18

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21 CRYSTAL LATTICES= orderly 3D repeating pattern arrangement of ions in ionic solids. Attraction between + and charges keeps the fixed positions. There are many types of crystal lattices which depend on the arrangement of ions. 21

22 Ionic Compound Properties can be explained by their strong attraction among ions within crystal lattice in the SOLID state. High melting point (it takes a lot of Kinetic Energy to separate the strong attraction among particles in the substance.) Poor conductors of electric current in SOLID STATE (ions are in fixed positions.) Good conductors when MELTED (ions are free flowing.) Ability to SHATTER when struck (ions get pushed next to same charged ions and REPEL.) 22

23 2 nd type of Chemical Bond= COVALENT BOND: Always formed between 2 NON metals (which have high ionization energies.) 2 atoms sharing a PAIR of electrons (single bond) SHARING 2 PAIR (double bond) SHARING 3 pair (triple bond) 23

24 Cl Cl S C S P P 24

25 Molecule= neutral group of atoms joined together by 1 or more covalent bonds held together by attractions between the shared electrons and protons in each nucleus (shared equally.) Diatomic molecules= when 2 of the same element chemically bond together. Many elements exist in nature this way: Br H O N Cl I F Bromine, Hydrogen, Oxygen, Nitrogen, Chlorine, Iodine & Fluorine 25

26 Writing/Naming MOLECULAR FORMULAS (Covalent Compounds) o o o o The name & formula describe the type and number of atoms in a molecule of the compound. (never simplify!) The most metallic (farthest left element, or lower) is written first. The name of the second element s ending is changed to ide. Greek PREFIXES before each element indicate the actually number of atoms of each in the molecule (except mono is never used for the FIRST element in the name.) o Examples: N 2 O 4 = dinitrogen tetraoxide NO 2 = nitrogen dioxide o The prefix indicates the subscript on that element 26

27 Covalent Compound Naming Prefixes: 27

28 What is the proper name of these compounds? O O N O O N O 28

29 UNEQUAL SHARING OF ELECTRONS IN CHEMICAL BONDS: In general elements on the RIGHT & TOP have a greater attraction for electrons than those on the right (except Noble Gases.) F has the strongest attraction of electrons! POLAR COVALENT BONDS= Covalent bond where electrons are NOT shared equally. i.e HCl Cl attracts more of the electrons than H, so the shared electrons spend more time near the Chlorine atom. When atoms form polar covalent bonds, the atom with the greater attraction for the electron has a partial negative charge, and the other atom has a partial positive charge. δ + H Cl δ electrons are pulled by the chlorine 29

30 When there are more than 2 elements (more than 1 covalent bond) the polarity depends on the type of atoms in the molecule and its shape. O=C=O is linear & NONPOLAR H H is bent (O has greater attraction for electron than H) so POLAR O 30

31 ATTRACTION BETWEEN PARTICLES IN COMPOUNDS: 1) Ionic Solids (Salts) have a strong attraction between FORMULA UNITS (each unit in an Ionic Compound i.e. CaCl 2 ) 2) Attraction between POLAR MOLECULES are STRONGER than attractions between NONPOLAR MOLECULES. Water is POLAR so it boils at a HIGHER temperature because the attraction between partially positive H and partially negative O hold the water molecules together. NONPOLAR Methane or Chlorine have LOW boiling points because it doesn t take a lot of energy to pull the molecules apart. 31

32 METALLIC BONDS: Valence electrons are free to move among the atoms in a metal. (Cation + in pool of shared electrons.) The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and surrounding valence electrons. The metallic bonds are stronger when they have more valence electrons (metals which are harder and have higher melting points.) Allow metals to be MALLEABLE because ions move to new spot, but are still surrounded by electrons. Can conduct electric current well because electrons are mobile. 32

33 ALLOYS= Mixture of 2 or more elements (one metal) to obtain desired qualities! *Metalurgy = Science of extracting metals from ores, refining metals and using metals. Copper + Tin = Bronze (hard and durable) Copper + Zinc = Brass (softer, more shiny, duller tone.) 33

34 Iron + Carbon = Steel STEEL ALLOYS vary in amounts of Carbon and other additives. Carbon bonds with Iron to form hard strong lattice. Stainless Steel = 10% Chromium. Less rust, more brittle. Al, Cu, Mg or Mn added for strength and are light 34

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36 Attachments writtingcovalentcompoundsws.doc writenamecmpsacad.doc SCIENCE FOUNDATIONS Chapter 6 Chemical Bonds FILLINS.doc covalentname.doc