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CH. 6 CHEMICAL BONDS

Holt

Updated November 2013

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.

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Chemical Structure representations

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Ball and stick model

StructuralModel

Space-filling model

Source: http://guweb2.gonzaga.edu/faculty/cronk/chemistry/L00-index.cfm?L00resource=water

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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.

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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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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.

www.ausetute.com.au/lewisstr.html

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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• http://commons.wikimedia.org/wiki/Image:Electron_dot.svg

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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.

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• http://www.promotega.org/UGA06004/ionic_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.

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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.

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Sodium becoming an ion

iss.cet.edu/electricity/pages/b11.xml

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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.

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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 -

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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

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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• http://www.iun.edu/~cpanhd/C101webnotes/composition/formioncmpds.html

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 2:1 Fe:Br is 1:3 Cr:O is 2:3

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6.2 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.

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Common NameMolecular FormulaLewis Formula Kekulé Formula• Methane CH4 •

• Ammonia NH3

• Methyl Alcohol CH4O

• Formaldehyde CH2O•

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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

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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.

www.uoregon.edu

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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

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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 100oC• BP for CO2 is -78oC

•

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Covalent bonds (sharing e’s)

Bonded hydrogen atoms showing equal charge distribution

Sample: H2

• http://www.beyondbooks.com/psc92/3c.asp

Hydrogen and bromide bond with an unequal charge distributionSample: HBr

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. CCl4

•

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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.

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• 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

http://en.wikibooks.org/wiki/General_Chemistry/Ionic_bonds

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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.

Polyatomic Ions

• are ions made of two or more atoms.• OH- hydroxide ion• CO3

2- carbonate ion

• NH4+ ammonium ion

• Samples: NaOH or Ca(OH)2

• ( ) are needed when more than one of a polyatomic ion is needed

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6.3 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 1st element and part of 2nd element with –ide at the end.

• CaCl2 is calcium chloride

• Al2O3 is aluminum oxide

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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] Fe2O3 [iron (III) oxide]

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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 CaBr2 calcium bromide

• Fe2O3 iron (III) oxide FeO iron (II) oxide

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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(NO3)2 is calcium nitrate

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Common Polyatomic Ions• Carbonate ion CO3 -2

• Hydroxide ion OH-1

• Nitrate ion NO3 -1

• Phosphate ion PO4 -3

• Ammonium ion NH4 +1• Sulfate ion SO4

-2

• Samples• CaSO4 calcium sulfate

• Ba(OH)2 barium hydroxide

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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

CO2 is carbon dioxide

N2O2 is dinitrogen dioxide

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Naming Covalent Compounds

• Write the true name of the 1st 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 2nd nonmetal with an –ide suffix and preceded by a numerical prefix equal to the subscript of the element.

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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 • BF3 boron trifluoride

• N2O4 dinitrogen tetraoxide

• C307 tricarbon heptaoxide

• N2O5 dinitrogen pentaoxide

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Molecular Formulas

• Molecular Formula – reports the actual number of atoms in one molecule of a compound

• Acetic acid C2H4O2 Glucose C6H12O6

• 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 CH20 Glucose CH2O

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.

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Hydrocarbons

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n-Alkane MolecularFormula

CondensedStructural Formula

Methane CH4 CH4

Ethane C2H6 CH3CH3

Propane C3H8 CH3CH2CH3

Butane C4H10 CH3(CH2)2CH3

Pentane C5H12 CH3(CH2)3CH3

Hexane C6H14 CH3(CH2)4CH3

Heptane C7H16 CH3(CH2)5CH3

Octane C8H18 CH3(CH2)6CH3

Nonane C9H20 CH3(CH2)7CH3

Decane C10H22 CH3(CH2)8CH343

• Alkanes – have only single covalent bonds. General pattern CnH2n+2

• Alkenes – have double C=C bonds. General pattern is CnH2n

• Alcohols have a hydroxyl (OH-) group. Example: isopropanol: (CH3)2CHOH

• 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

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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.

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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!•