CHAPTER 19

CHAPTER 20

CHEMICALBONDING

Stability in Bonding

•Most matter is found incompounds {ie air, water,salt}

•Compounds haveproperties unlike those oftheir individual elements

•Salt: NaCl= Na + Cl

•Na is a grey, soft metalthat reacts violently w/water

•Cl is a greenish-yellow gasthat is toxic if inhaled

•1 atom Na + 1 atom Cl = NaCl

•NaCl is a chemical formula

•Chemically combine toform something we put onour french fries!

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Sodium

Chlorine

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H2O ≠ H2O ≠ H2O

•Numbers in some chemicalformulas are called subscripts

•Means “written below”

•This # tells how many atoms ofthat element combine with theother element(s)

•Ammonia: NH3 = 1 N atom forevery 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 thathold atoms together in acompound

•Chemical Formula: tellswhat elements it containsw/ symbols

•Tells ratio of the atoms ofthose atoms w/ subscripts

•Elements bond to becomechemically stable (happy )

•They become resistant tochange

•Outer E level completelyfilled with e- (usually 8 e-)

•Gaining, losing,or sharing e-cause chemicalchange

20-2 Types of Bonds

Ions are atoms that have lost or gained ane-

•This gives them a positive (+, lose e-) ornegative (-, gain e-) charge

•Draw Lewis structures for each element

•Put brackets around the symbol [ ]

•Then write a superscript + or – sign (seebottom of pg 609 or top of pg 603) outside of thebrackets

Ionic Bonds

•Force of attraction between theopposite charges of the ions in anionic compound

•Atoms gain or lose e- to becomestable

•Metals usually lose e- (# in outer Elevel)

•Non-metals usually gain e-

•Now both atoms are stable (happy )

Ionic bonding

•NaCl

•Whiteboard practice:

•MgF2

•CaCl2

•LiBr

•KI

•Mg3P2

NaClLewisDot

LewisDotCl

Covalent bonding

•Molecules are formed when e- are SHARED

•Sharing e- to become stable (8 e-/outer level) ismore 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: polarmolecules are between 2 differentnon-metal elements

•Unequal sharing causes the moleculeto 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 ornegative

Covalent bonding forms molecules which can bepolar or non-polar

Elements that are close together on the periodictable (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

•Oxidation # is a + or - # assigned toan element to show its combiningability in a compound

•It indicates how many e- an atomhas lost, gained or shared whenbonding

•NaCl: Na loses 1 e- : 1+ oxidation #

• Cl gains 1 e- : 1- oxidation #

•Write the oxidation #’s on yourperiodic table from pg 616

20.3 Writing Formulasand Naming Compounds

•Some elements have more than1 oxidation #

•Usually the Transition elements

•Use Roman numerals to showthe different oxidation #’s

•Copy Table 2 from pg 616 ontothe back of your periodic table

•Do the same for Table 3, pg 618and Table 4, pg 619 and Table 5,pg 621

How to write binary ionicformulas

•Binary compound: composed of 2different elements (ie NaCl)

•1) write the symbol for the elementsw/ the (+) oxidation # (H & metals are +)

•2) then write the symbol of theelement w/ the (-) oxidation # (non-metals)

•3) add subscripts so the sum of theoxidation #’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 becomesthe subscript for N; ox# of N becomes the subscriptfor 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 1ox # (check the back of yourperiodic table), use the ox # of the(-) element to figure out the ox # ofthe (+) element; use a Romannumeral after the element’s name

•3) use Table 3 (back of your PT) toname the second element

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 weshould use Copper (I)

•3) I is iodine, which changes toiodide in binary compounds

•4) Copper (I) iodide

WHITEBOARD PRACTICE

•MgF2

•PbO2

•Na2O

•LiBr

•BaS

•CuO

•FeF3

•Cr2O3

MCj04107170000[1]

Compounds with Polyatomic Ions

•Poly: many, so polyatomic: havingmany atoms

•Polyatomic ion: positively ornegatively charge group of atomsthat act as one when bonding

•Table 4 is just a short list

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Naming with polyatomic ions

•1) Write positive part first

•2) Use Table 4 from the back ofyour PT

•Example: NaOH

•1) Na is positive: sodium

•2) OH : hydroxide

•3) sodium hydroxide

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Whiteboard practice

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•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 aroundpolyatomic ion when more than one of thation 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

MPj04003970000[1]

Compounds with added water

•Hydrate is a compound that haswater chemically attached to itsions

•CoCl2·6H2O: Cobalt chloride hexahydrate

•Hexa= 6; hydrate= H2O

•Ca(NO3)2·3H2O : ?

•Mg3(PO4)2·4H20 : ?

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