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1 CH. 6 CHEMICAL BONDS Holt Updated November 2013.

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1 1 CH. 6 CHEMICAL BONDS Holt Updated November 2013

2 6.1 Chemical Bonds These are the forces that hold atoms or ions together to form compounds. Ionic bond – electrons are transferred from one atom to another resulting in ions Covalent bond – electrons are shared Network structures – –strong bonds cause high mp and bp, also strong and inflexible. –Can be formed by + and – ion bonding Molecular structures – (C, H, O) have weaker bonds and lower mp and bp. 2

3 Chemical Structure representations 3 Ball and stick model Structural Model Space-filling model Source: index.cfm?L00resource=water

4 4 CRYSTAL LATTICES SOLIDS WHOSE PARTICLES ARE ARRANGED IN A LATTICE STRUCTURE ARE CALLED CRYSTALS. THE PROPERTIES OF AN IONIC COMPOUND CAN BE EXPLAINED BY THE STRONG ATTRACTIONS AMONG IONS WITHIN A CRYSTAL LATTICE.

5 5 Ch 6 Assignments!! Section 6.1: 182/1-6 AND CH. 6 VOCABULARY on page 209 SECTION 6.2: 190/1-9 SECTION 6.3: 196/1-7 SECTION 6.4: 204/1-6 WRITE THE QUESTIONS!

6 6 6.2 IONIC BONDING STABLE ELECTRON CONFIGURATIONS WHEN THE HIGHEST OCCUPIED ENERGY LEVEL OF AN ATOM IS FILLED WITH ELECTRONS, THE ATOM IS STABLE AND NOT LIKELY TO REACT.

7 7 ELECTRON DOT DIAGRAM AN ELECTRON DOT DIAGRAM IS A MODEL OF AN ATOM IN WHICH EACH DOT REPRESENTS A VALENCE ELECTRON. THE SYMBOL IN THE CENTER REPRESENTS THE NUCLEUS AND ALL THE OTHER ELECTRONS IN THE ATOM.

8 8 /Image:Electron_dot.svg

9 9 IONIC BONDS ELEMENTS THAT DON’T HAVE COMPLETE SETS OF VALENCE ELECTRONS TEND TO REACT. SOME ELEMENTS ACHIEVE STABLE ELECTRON CONFIGURATIONS THROUGH THE TRANSFER OF ELECTRONS BETWEEN ATOMS. Bonding occurring as a result of transfer of electrons are ionic bonds.

10 10 bonds.html Sodium loses 1 electron Its charge becomes +1 (aka a cation) Chlorine gains 1 electron Its charge becomes -1 (aka an anion) Ionic bonding occurs between a metal and a nonmental.

11 11 FORMATION OF IONS WHEN AN ATOM GAINS OR LOSES AN ELECTRON, THE NUMBER OF ELECTRONS IS NO LONGER EQUAL TO THE NUMBER OF PROTONS. THE CHARGE ON THE ATOM IS NOT BALANCED AND THE ATOM IS NOT NEUTRAL. AN ATOM THAT HAS A NET POSITIVE OR NEGATIVE ELECTRIC CHARGE IS CALLED AN ION.

12 12 Sodium becoming an ion iss.cet.edu/electricity/pages/b11.xml

13 13 FORMATION OF IONS AN ION WITH A NEGATIVE CHARGE IS AN ANION. AN ION WITH A POSITIVE CHARGE IS CALLED A CATION. FORMATION OF IONIC BONDS A CHEMICAL BOND IS THE FORCE THAT HOLDS ATOMS OR IONS TOGETHER. AN IONIC BOND IS THE FORCE THAT HOLDS CATIONS AND ANIONS TOGETHER. It is an electrostatic bond.

14 14 Which one becomes the cation? (The positive ion) Sodium What is its charge? Na + Which one becomes the anion? (The negative ion) Chlorine What is its charge? Cl -

15 15 IONIZATION ENERGY AN ELECTRON CAN MOVE TO A HIGHER ENERGY LEVEL WHEN AN ATOM ABSORBS ENERGY. THE ENERGY ALLOWS ELECTRONS TO OVERCOME THE ATTRACTION OF PROTONS IN THE NUCLEUS. THE AMOUNT OF ENERGY USED TO REMOVE AN ELECTRON IS CALLED IONIZATION ENERGY. Pattern: increase left to right across a period in the Periodic Table

16 16 IONIC COMPOUNDS COMPOUNDS THAT CONTAIN IONIC BONDS ARE IONIC COMPOUNDS, WHICH CAN BE REPRESENTED BY CHEMICAL FORMULAS. A CHEMICAL FORMULA IS A NOTATION THAT SHOWS WHAT ELEMENTS A COMPOUND CONTAINS AND THE RATIO OF THE ATOMS OR IONS OF THESE ELEMENTS IN THE COMPOUND.

17 17 Chemical Formulas. The subscripts show the number of atoms of an element. 1 Ca 2 Cl in CaCl 2 Ratios of Atoms in these above compounds: Ca:Cl is 1:2 Ba:O is 1:1 K:S is 2:1Fe:Br is 1:3 Cr:O is 2:3

18 18

19 COVALENT BONDS SHARING ELECTRONS A CHEMICAL BOND IN WHICH TWO ATOMS SHARE A PAIR OF VALANCE ELECTRONS IS CALLED A COVALENT BOND. Nonmetal – nonmetal bonds are covalent. They form molecules. THE TYPE OF ATOMS IN A MOLECULE AND ITS SHAPE ARE FACTORS THAT DETERMINE WHETHER A MOLECULE IS POLAR OR NONPOLAR.

20 20 Common NameMolecular FormulaLewis Formula Kekulé Formula Methane CH4 Ammonia NH3 Methyl Alcohol CH4O Formaldehyde CH2O

21 21 COVALENT BONDS MULTIPLE COVALENT BONDS EACH PAIR OF SHARED ELECTRONS ARE REPRESENTED BY A LONG DASH IN THE STUCTURAL FORMULA. WHEN TWO ATOMS SHARE THREE ELECTRONS, THE BOND IS CALLED A TRIPLE BOND. WHEN TWO ATOMS SHARE TWO ELECTRONS, THE BOND IS CALLED A DOUBLE BOND

22 22 UNEQUAL SHARING OF ELECTRONS POLAR COVALENT BONDS A COVALENT BOND IN WHICH ELECTRONS ARE NOT SHARED EQUALLY IS CALLED A POLAR COVALENT BOND. WHEN ATOMS FORM A POLAR COVALENT BOND,THE ATOM WITH THE GREATER ATTRACTION OF ELECTRONS HAS A PARTIAL NEGATIVE CHARGE. THE OTHER ATOM HAS A PARTIAL NEGATIVE CHARGE.

23 23 Water is Polar Covalent academic.brooklyn.cuny.edu/.../page/polar_c.htm *it has two polar single bonds *its molecule has a bent shape *it has high boiling point because of strong molecular attraction

24 24 Interesting Fact Because water molecules are polar and Carbon dioxide molecules are nonpolar (shared equally) water has a higher boiling point than carbon dioxide. ATTRACTIONS BETWEEN POLAR MOLECULES ARE STRONGER THAN ATTRACTIONS BETWEEN NONPOLAR MOECULES. BP for water is 100 o C BP for CO 2 is -78 o C

25 25

26 26 Covalent bonds (sharing e’s) Bonded hydrogen atoms showing equal charge distribution Sample: H 2 Hydrogen and bromide bond with an unequal charge distribution Sample: HBr

27 Shortcut Ionic compounds are formed between: –A metal and a nonmetal, i.e. NaCl Covalent compounds are formed between: –Hydrogen and a nonmetal, i.e. HCl –Two nonmetals, i.e. CCl 4 27

28 28 THE STRUCTURE OF METALS METALLIC BONDS A METALLIC BOND IS THE ATTRACTION BETWEEN A METAL CATION AND THE SHARED ELECTRONS AROUND IT. THE CATIONS IN A METAL FORM A LATTICE THAT IS HELD IN PLACE BY STRONG METALLIC BONDS BETWEEN THE CATIONS AND THE SURROUNDING VALENCE ELECTRONS.

29 29 The ions arrange themselves into a lattice where each ion is surrounded by ions of the opposite type. Metal cations are attracted through a shared pool of electrons. Similar to ionic bonding because of attraction of + and - charged particles. Characteristics NaCl. KNO3 Ionically bonded substances typically have the following characteristics. High melting point Solid at room temp Brittle (can shatter) Some dissolve in water Conduct electricity when dissolved or melted Chemistry/Ionic_bonds

30 30 EXPLAINING PROPERTIES OF METALS THE MOBILITY OF ELECTRONS WITHIN A METAL LATTICE EXPLAINS SOME OF THE PROPERTIES OF METALS. THE ABILITY TO CONDUCT AN ELECTRIC CURRENT AND MALLEABILITY ARE TWO IMPORTANT PROPERTIES OF METALS.

31 Polyatomic Ions are ions made of two or more atoms. OH - hydroxide ion CO 3 2- carbonate ion NH 4 + ammonium ion Samples: NaOH or Ca(OH) 2 ( ) are needed when more than one of a polyatomic ion is needed 31

32 NAMING COMPOUNDS AND WRITING FORMULAS DESCRIBING IONIC COMPOUNDS THE NAME OF AN IONIC COMPOUND MUST DISTINGUISH THE COMPOUND FROM THE OTHER IONIC COMPOUNDS CONTAINING THE SAME ELEMENTS. Full name of 1 st element and part of 2 nd element with –ide at the end. CaCl 2 is calcium chloride Al 2 O 3 is aluminum oxide

33 33 DESCRIBING IONIC COMPOUNDS BINARY IONIC COMPOUNDS –Samples: NaCl CaO A COMPOUND MADE FROM ONLY TWO ELEMENTS IS A BINARY COMPOUND. THE ALKALI METALS, ALKALINE EARTH METALS, AND ALUMINUM FORM IONS WITH POSITIVE CHARGES EQUAL TO THE GROUP NUMBER. MANY TRANSITIONAL METALS FORM MORE THAN ONE TYPE OF ION. FeO [iron (II) oxide] Fe 2 O 3 [iron (III) oxide]

34 34 Naming Ionic Compounds with 2 Elements Write the true name of the metal (+ion) first. If the metal is a transition metal with more than one charge, write the charge as a Roman numeral in parenthesis after the metal. Write the name of the nonmetal (-ion with an –ide suffix. NaCl sodium chloride CaBr 2 calcium bromide Fe 2 O 3 iron (III) oxide FeO iron (II) oxide

35 35 DESCRIBING IONIC COMPOUNDS POLYATOMIC IONS A COVALENTLY BONDED GROUP OF ATOMS THAT HAVE A POSITIVE OR NEGATIVE CHARGE AND ACTS AS A UNIT IS CALLED A POLYATOMIC ION. Ca(OH) 2 is calcium hydroxide Ca(NO 3 ) 2 is calcium nitrate

36 36 Common Polyatomic Ions Carbonate ion CO 3 -2 Hydroxide ionOH -1 Nitrate ionNO 3 -1 Phosphate ionPO 4 -3 Ammonium ionNH4 +1 Sulfate ionSO 4 -2 Samples CaSO 4 calcium sulfate Ba(OH) 2 barium hydroxide

37 37 DESCRIBING MOLECULAR COMPOUNDS THE NAME AND FORMULA OF A MOLECULAR COMPOUND DESCRIBE THE TYPE AND NUMBER OF ATOMS IN A MOLECULE OF THE COMPOUND. CO is carbon monoxide CO 2 is carbon dioxide N 2 O 2 is dinitrogen dioxide

38 38 Naming Covalent Compounds Write the true name of the 1 st nonmetal (one furthest to the right in periodic table) with a numerical prefix equal to the subscript of the element. If there is only one atom of the element, no prefix is required. Write the name of the 2 nd nonmetal with an –ide suffix and preceded by a numerical prefix equal to the subscript of the element.

39 39 Prefixes for Covalent Compounds 1 – mono 2 – di- 3 – tri– 4 – tetra- 5 – penta 6 – hexa- 7 – hepta- 8 – octo- 9 – nona- 10 – deca- CO carbon monoxide BF 3 boron trifluoride N 2 O 4 dinitrogen tetraoxide C tricarbon heptaoxide N 2 O 5 dinitrogen pentaoxide

40 40 Molecular Formulas Molecular Formula – reports the actual number of atoms in one molecule of a compound Acetic acid C 2 H 4 O 2 Glucose C 6 H 12 O 6 Empirical Formula – simplest formula of compound that tells the smallest whole number ratio of atoms in the compound. If subscripts have a common factor, divide each subscript by that factor. Acetic acid CH 2 0 Glucose CH 2 O

41 6.4 Organic and Biochemical Compounds Organic compounds contain mainly carbon. Other elements present may include: H, O, N, S, and P. Excluding carbonates and oxides. 41

42 Hydrocarbons 42

43 n-AlkaneMolecular Formula Condensed Structural Formula MethaneCH 4 EthaneC2H6C2H6 CH 3 PropaneC3H8C3H8 CH 3 CH 2 CH 3 ButaneC 4 H 10 CH 3 (CH 2 ) 2 CH 3 PentaneC 5 H 12 CH 3 (CH 2 ) 3 CH 3 HexaneC 6 H 14 CH 3 (CH 2 ) 4 CH 3 HeptaneC 7 H 16 CH 3 (CH 2 ) 5 CH 3 OctaneC 8 H 18 CH 3 (CH 2 ) 6 CH 3 NonaneC 9 H 20 CH 3 (CH 2 ) 7 CH 3 DecaneC 10 H 22 CH 3 (CH 2 ) 8 CH 3 43

44 Alkanes – have only single covalent bonds. General pattern C n H 2n+2 Alkenes – have double C=C bonds. General pattern is C n H 2n Alcohols have a hydroxyl (OH - ) group. Example: isopropanol: (CH 3 ) 2 CHOH Polymers are molecules containing a long chain of smaller molecules. Some are flexible or elastic. –Natural: rubber, wood, cotton wool, DNA –Artificial: plastic milk jugs contain polyethylene 44

45 Biochemical Compounds These, such as carbohydrates, proteins, and DNA (polymer that stores genetic information), are essential to life. Carbohydrates are made of glucose (sugars, starches that provide energy to living things) Proteins are complex polymers of amino acids that provide structure and functions to parts of cells. Amino acids each contain an amino group (-NH2), a carboxyl group (-COOH) and a side group that give each amino acid its unique properties. 45

46 46 Ch 6 Assignments!! Section 6.1: 182/1-6 AND CH. 6 VOCABULARY on page 209 SECTION 6.2: 190/1-9 SECTION 6.3: 196/1-7 SECTION 6.4: 204/1-6 WRITE THE QUESTIONS!


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