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CHAPTER 20

CHAPTER 20. CHEMICAL BONDING. Stability in Bonding. Most matter is found in compounds {ie air, water, salt} Compounds have properties unlike those of their individual elements Salt: NaCl= Na + Cl Na is a grey, soft metal that reacts violently w/ water

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CHAPTER 20

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  1. CHAPTER 20 CHEMICAL BONDING

  2. Stability in Bonding • Most matter is found in compounds {ie air, water, salt} • Compounds have properties unlike those of their individual elements • Salt: NaCl= Na + Cl • Na is a grey, soft metal that reacts violently w/ water • Cl is a greenish-yellow gas that is toxic if inhaled • 1 atom Na + 1 atom Cl = NaCl • NaCl is a chemical formula • Chemically combine to form something we put on our french fries!

  3. H2O ≠ H2O ≠ H2O • Numbers in some chemical formulas are called subscripts • Means “written below” • This # tells how many atoms of that element combine with the other element(s) • Ammonia: NH3 = 1 N atom for every 3 H atoms 1N:3H ratio

  4. Try these! • SiO2 silicon dioxide • C2H5OH ethanol • H2SO4 sulfuric acid • C6H12O6 sugar • KMnO4potassium permanganate

  5. Chemical Formula: tells what elements it contains w/ symbols Tells ratio of the atoms of those atoms w/ subscripts Elements bond to become chemically stable (happy ) They become resistant to change Outer E level completely filled with e- (usually 8 e-) Gaining, losing, or sharing e- cause chemical change Chemical bonds are forces that hold atoms together in a compound

  6. 20-2 Types of Bonds Ions are atoms that have lost or gained an e- • This gives them a positive (+, lose e-) or negative (-, gain e-) charge • Draw Lewis structures for each element • Put brackets around the symbol [ ] • Then write a superscript + or – sign (see bottom of pg 609 or top of pg 603) outside of the brackets

  7. Ionic Bonds • Force of attraction between the opposite charges of the ions in an ionic compound • Atoms gain or lose e- to become stable • Metals usually lose e- (# in outer E level) • Non-metals usually gain e- • Now both atoms are stable (happy )

  8. Ionicbonding • NaCl • Whiteboard practice: • MgF2 • CaCl2 • LiBr • KI • Mg3P2

  9. Covalent bonding • Molecules are formed when e- are SHARED • Sharing e- to become stable (8 e-/outer level) is more common than losing/gaining e- • Diatomic molecules: 2 atoms of the same element • Cl2 , O2 , H2 , N2 , F2 • These would be nonpolar molecules: they share e- equally

  10. Covalent bonding, cont. • e- not always shared equally: polar moleculesare between 2 different non-metal elements • Unequal sharing causes the molecule to have a (+) and a (–) end • e- spend more time near the O than the 2 H atoms

  11. CHEMICAL BONDING REVIEW Ionic bonding forms ions which can be positive or negative Covalent bonding forms molecules which can be polar or non-polar Elements that are close together on the periodic table (non-metals) usually form covalent bonds Elements far apart on the periodic table (metals & non-metals) form ionic bonds Extra Credit!!! Draw dot diagram for sugar: C6 H12 O6

  12. 20.3 Writing Formulas and Naming Compounds • Oxidation # is a + or - # assigned to an element to show its combining ability in a compound • It indicates how many e- an atom has lost, gained or shared when bonding • NaCl: Na loses 1 e- : 1+ oxidation # • Cl gains 1 e- : 1- oxidation # • Write the oxidation #’s on your periodic table from pg 616

  13. Some elements have more than 1 oxidation # • Usually the Transition elements • Use Roman numerals to show the different oxidation #’s • Copy Table 2 from pg 616 onto the back of your periodic table • Do the same for Table 3, pg 618 and Table 4, pg 619 and Table 5, pg 621

  14. How to write binary ionic formulas • Binary compound: composed of 2 different elements (ie NaCl) • 1) write the symbol for the elements w/ the (+) oxidation # (H & metals are +) • 2) then write the symbol of the element w/ the (-) oxidation # (non-metals) • 3) add subscripts so the sum of the oxidation #’s of the atoms are zero

  15. Let’s Practice! • Bromine and Potassium • 1) Potassium is + : K1+ • 2) Bromine is - : Br1- • 3) (1+) + (1-) = 0, so no subscripts are needed • 4) KBr • Nitrogen and Magnesium • 1) Magnesium is + : Mg2+ • 2) Nitrogen is - : N3- • 3) (2+) + (3-) ≠ 0, so you need to add subscripts • 4) Use crossover method: the ox# of Mg becomes the subscript for N; ox# of N becomes the subscript for Mg: Mg3N2 • DO NOT USE + OR – SIGN IN SUBSCRIPT!!!

  16. PRACTICE WITH WHITEBOARDS • Flourine and Lithium • Chlorine and Aluminum • Calcium and Oxygen • Oxygen and Sodium • Potassium and Chlorine • Strontium and Sulfur • Beryllium and Nitrogen • Iodine and Rubidium

  17. Naming chemical compounds • 1) Write the name of the (+) element • 2) If this element has more than 1 ox # (check the back of yourperiodic table), use the ox # of the (-) element to figure out the ox # of the (+) element; use a Roman numeral after the element’s name • 3) use Table 3 (back of your PT) to name the second element

  18. Let’s Practice! • CuI • 1) Cu is (+) : Copper (is it a ‘specialion’? Look on the back of your PT) • 2) I is (-) : it’s ox # is (1-), so we should use Copper (I) • 3) I is iodine, which changes to iodide in binary compounds • 4) Copper (I) iodide

  19. WHITEBOARD PRACTICE • MgF2 • PbO2 • Na2O • LiBr • BaS • CuO • FeF3 • Cr2O3

  20. Compounds with Polyatomic Ions • Poly: many, so polyatomic: having many atoms • Polyatomic ion: positively or negatively charge group of atoms that act as one when bonding • Table 4 is just a short list

  21. Naming with polyatomic ions • 1) Write positive part first • 2) Use Table 4 from the back of your PT • Example: NaOH • 1) Na is positive: sodium • 2) OH : hydroxide • 3) sodium hydroxide

  22. Whiteboard practice • Cu(OH)2 • CaCO3 • Al(C2H3O2)3 • (NH4)3PO4 • CuSO4 • Ba(ClO3)2 • NH4Cl • PbCO3

  23. Writing formulas w/ polyatomics • Same rules as for binary compounds • Plus step 4: write parentheses around polyatomic ion when more than one of that ion is needed • Example: iron III nitrate • 1) iron (III) = Fe3+ • 2) nitrate = NO3 1- • 3) You will need 3 (NO3) to make ox #’s = zero • 4) Subscript is written outside the ( ) otherwise it would look like FeNO33 • Fe(NO3)3

  24. WHITEBOARD PRACTICE!! • Potassium chlorate • Ammonium chloride • Sodium sulfate • Magnesium chlorate • Lead (II) carbonate • Chromium (III) phosphate • Lithium nitrate • Calcium acetate

  25. Compounds with added water • Hydrate is a compound that has water chemically attached to its ions • CoCl2·6H2O: Cobalt chloride hexahydrate • Hexa= 6; hydrate= H2O • Ca(NO3)2·3H2O : ? • Mg3(PO4)2·4H20 : ?

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