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Chemical Bonding: Understanding Stability and Formation

Learn about ionic and covalent bonds, chemical formulas, and how atoms bond to become stable. Discover the different types of bonds and practice writing chemical formulas and naming compounds.

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Chemical Bonding: Understanding Stability and Formation

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  1. CHAPTER 19 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. 19-2 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 581) 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. 19-3 Writing Formulas & 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 588

  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 588 onto the back of your periodic table • Do the same for Table 3, pg 590 and Table 4, pg 591 and Table 5, pg 593

  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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