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 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!

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

Try these! SiO2 silicon dioxide C2H5OH ethanol H2SO4 sulfuric acid C6H12O6 sugar KMnO4 potassium permanganate

Chemical bonds are forces that hold atoms together in a compound 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

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

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 )

Ionic bonding NaCl Whiteboard practice: MgF2 CaCl2 LiBr KI Mg3P2

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

Covalent bonding, cont. e- not always shared equally: polar molecules are 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

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

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

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

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

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!!!

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

Naming chemical compounds 1) Write the name of the (+) element 2) If this element has more than 1 ox # (check the back of your periodic 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

Let’s Practice! CuI 1) Cu is (+) : Copper (is it a ‘special ion’? 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

WHITEBOARD PRACTICE MgF2 PbO2 Na2O LiBr BaS CuO FeF3 Cr2O3

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

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

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

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

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

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 : ?