Chemistry & Physics

UNIT 4: CHEMICAL BONDING

Chemistry

Periodic table

Matter

Atoms

Chemical bonding

Chemical reaction

Electrolytes

Hydrocarbons

Organic chemistry

Today

• Molecules• Chemical bonding

– Ionic bonding– Covalent bonding– Hydrogen bonding

• Formulas• Chemical calculations

– Oxidation number– Molar mass– Mole

Chemical bonds

COVALENT BONDING

IONIC BONDING

HYDROGEN BONDING

Molecules

• Combination of two or more atoms– Same elements– Different elements

Nitrogen: NN or N2

Glucose: C6H12O6

Water: HOH or H2O

Carbon dioxide: OCO or CO2

Sackheim’s Chemistry: Chapter 4

Sulfur: cyclic S8

diatomic

polyatomic

Formula (1)

• Group of symbols = Formula– Represents elements present in a substance

2 atoms of oxgen: 2 O (no molecule)

Sodium chloride (salt): NaCl

Glucose (sugar):C6H12O6

1 molecule of oxygen: O2 (a molecule)

Sackheim’s Chemistry: Chapter 4

What holds

atoms together?

coefficient

subscript

Lewis structure

• Electron-dot (or Lewis) structure– Simplified structure of atom

• Nucleus + Lower energy electrons: Symbol of element• Valence electrons (highest energy electrons): Dots

Sodium:

Na

Carbon:

C

Neon:

Ne

Chloride:

Cl

• Octet rule– Atoms are stable when outer energy level filled with 8 electrons (8 = octet)

• Noble gases: Ne, Ar, Kr, Xe stable– Not 8 valence electrons? Lose, gain, share electrons

• Other atoms: Na, C, Cl, etc.• Process is responsible for bond formation

· · ··· · ··· ·

· · ··· ·· ···

Sackheim’s Chemistry: Chapter 4

Ion formation

Sackheim’s Chemistry: Chapter 4

• Formation of ions (stable)– Metals: lose electrons– Nonmetals: gain electrons

Ions

• Atom that has lost/gained electrons: “ion”– Metals: positive charge equal to number of electons lost

“cations”– Nonmetals: negative charge equal to number of electrons gained

“anions”

• Human body– Cations: Na+, K+, Ca2+

– Anions: Cl-

• Size of ions– Cations: Less electrons, smaller ionic radius– Anions: More electrons, larger ionic radius

Sackheim’s Chemistry: Chapter 4

Polyatomic ions

Formula Name

SO42- Sulfate

NO3- Nitrate

PO43- Phosphate

CO32- Carbonate

OH- Hydroxide

HCO3- Bicarbonate

NH4+ Ammonium

Sackheim’s Chemistry: Chapter 4

Group of atoms acting as one ion

Ionic bonding (1)

• Ionic bond– Transfer of electron(s) from one atom to another– Formation of ions which attract one another

• NaCl– Transfer of one electron from sodium to chloride– Na+ and Cl- will be attracted to each other: electrostatic attraction

• MgCl2

– Transfer of two electrons from magnesium to two chlorine atoms– Each ion has completed highest energy level: 8 electrons

Sackheim’s Chemistry: Chapter 4

Ionic bonding (2)

Nomenclature

• Naming of ionic compounds

– Name of positive ion + stem of negative ion + “ide”• NaCl: sodium + chlor + ide = sodiumchloride• MgCl2: magnesium + chlor + ide = magnesiumchloride• KI : potassium + iod + ide = potassiumiodide

– Name of positive ion + name of polyatomic ion• LiOH: lithium + hydroxide = lithiumhydroxide• K3PO4: potassium + phosphate = potassiumphosphate

• NaHCO3-: sodium + bicarbonate = sodiumbicarbonate

Sackheim’s Chemistry: Chapter 4

Covalent bonding

Cl Cl‒

H Cl‒

• Sharing, no loss/gain• Obey octet rule• “Noble gas structure”• Metals/ions not involved

• Exception: H• Only two electrons

N≡N

O=C=O• 2 shared electron pairs• Double bond

• 3 shared electron pairs• Triple bond

Sackheim’s Chemistry: Chapter 4

covalent bond

double bond

triple bond

Nonpolar and polar bonds (1)

Cl Cl‒

H Cl‒

N≡N

O=C=O

H Cl‒

O=C=O

δ+ δ-

δ+ δ-δ-

• Nonpolar (apolar) bonds– Atoms are identical– Electrons shared equally

• Polar bonds– Electrons not shared equally– Electronegativity (e.n.)– Higher e.n. = stronger attraction– Partial charge (δ), no ions!

Electronegativity of elements

F O N, Cl Br C, S I H

4.0 3.5 3.1 2.8 2.5 2.4 2.1

Sackheim’s Chemistry: Chapter 4

Attraction of an atom for electrons“electron love”

Nonpolar and polar bonds (2)

Nomenclature

• Naming of covalent compounds

– Prefix + name of first element + prefix + stem of second element + “ide”• H2O: di + hydrogen + (mono) + ox + ide = dihydrogen oxide (water)

• CCl4: (mono) + carbon + tetra + chlor + ide = carbon tetrachloride

• P2O5: di + phosphorus + penta + ox + ide = diphosphorus pentaoxide

– Prefixes• 1 = mono• 2 = di• 3 = tri• 4 = tetra• 5 = penta• 6 = hexa

Sackheim’s Chemistry: Chapter 4

Hydrogen bonding

• Water (H2O)– Polar substance, negative and positive side: dipole

• Hydrogen bond (H-bond)– “Between molecules”– Positive end of one molecule attracks negative end of another molecule– Globular shape of proteins and helical shape of DNA– Many unusual properties of H2O!

Sackheim’s Chemistry: Chapter 9

Network of hydrogen bonding

hydrogen bond

covalent bond

Water

EXPERIMENT 002Title: Water SkinTopic: Hydrogen bonding

1. Put the paperclip on water surface2. Watch the result

3. Add two drops of soap detergent near the paper clip

4. Watch the result

What’s happening?

• Why does the paperclip float on top of water?– Hydrogen bonding– Water particles at the surface only bind to particles next/below them – Surface acts as skin: surface tension– Surface tension strong enough to support paperclip– Nature: water striders use the water skin

• Why does the paperclip sink when soap is added?– Soap disrupts hydrogen bonding: paperclip sinks

Formula (2)

• Definition– Group of symbols that represent the elements

present in a substance– Emperical vs. molecular formula

• Empirical (simplest) formula – Represents relative number of atoms present in the

substance– Ionic compounds (salts arrange in lattice)

• NaF, NaCl, KOH, MgCl2

• Molecular formula– Represents actual number of atoms present in the

substance– Covalent compounds

• H2O2, C2H6O, C6H12O6

Sackheim’s Chemistry: Chapter 5

Formula (3)

• Definition– Group of symbols that represent the elements present in a substance– Lewis vs. structural formula

• Lewis formula– Representing all electronpairs (bonds and lone pairs)– Lone pairs: electron pairs not involved in bonding

• Structural formula– Representing only bonds (without lone pairs)

lone pair

3D molecular shape

• Valence shell electron-pair repulsion (VSEPR) theory– Predict 3D molecular shape– Electron pairs repel one another: minimize repulsions– Electron pairs try to get as far as possible from each other

HCl

CH4

H2O

Sackheim’s Chemistry: Chapter 4NH3

Chemical calculations

COMPOSITION

MOLES

MOLECULAR MASS

OXIDATION STATE

Oxidation number

• In ions– Equal to charge of the ion– Equal to number of electrons

lost/gained

• In compounds– The sum of oxidation numbers in a

compound equals zero

Sackheim’s Chemistry: Chapter 6

Cation Oxidation state

Anion Oxidation state

H+ +1 F- -1

Na+ +1 Cl- -1

Mg2+ +2 Br- -1

Fe2+ +2 I- -1

Fe3+ +3 S2- -2

Al3+ +3 O2- -2

Calculating oxidation number

Sackheim’s Chemistry: Chapter 6

Using oxidation number

• The sum of oxidation numbers in a compound equals zero

• MgCl? – Mg = +2– Cl = -1

• AlO?– Al = +3– O = -2

1 Mg and 2 Cl makes zero: MgCl2

2 Al and 3 O makes zero: Al2O3

Sackheim’s Chemistry: Chapter 6

Cation Oxidation state

Anion Oxidation state

H+ +1 F- -1

Na+ +1 Cl- -1

Mg2+ +2 Br- -1

Fe2+ +2 I- -1

Fe3+ +3 S2- -2

Al3+ +3 O2- -2

Molecular mass

• Sum of atomic masses of all atoms present in one molecule (in u or g/mol)– N2 : 2 x 14 = 28 u

– HCl : 1 + 35 = 36 u

– CO2 : 12 + (2 x 16) = 44 u

– NaHCO3 = 23 + 1 + 12 + (3 x 16) = 84 u

– C6H12O6 = (6 x 12) + (12 x 1) + (6 x 16) = 180 u

HCl

N2

CO2

C6H12O6

(glucose)

NaHCO3

Sackheim’s Chemistry: Chapter 5

Mass percentage

• Relative atomic mass (percentage) of the elements present in the molecule– C6H12O6: Glucose

%𝑪=𝒎𝒂𝒔𝒔𝒐𝒇 𝑪𝒊𝒏𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒎𝒂𝒔𝒔𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆

×𝟏𝟎𝟎=𝟔×𝟏𝟐𝟏𝟖𝟎

×𝟏𝟎𝟎=𝟒𝟎%

%𝑯=𝒎𝒂𝒔𝒔𝒐𝒇 𝑯 𝒊𝒏𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆

𝒎𝒂𝒔𝒔𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆×𝟏𝟎𝟎=

𝟏𝟐×𝟏𝟏𝟖𝟎

×𝟏𝟎𝟎=𝟕%

%𝑶=𝒎𝒂𝒔𝒔𝒐𝒇 𝑶 𝒊𝒏𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒎𝒂𝒔𝒔𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆

×𝟏𝟎𝟎=𝟔×𝟏𝟔𝟏𝟖𝟎

×𝟏𝟎𝟎=𝟓𝟑%

Sackheim’s Chemistry: Chapter 5

100 %

Large, larger, largest

• Large numbers need large units

9.46 × 1015 meter = 1 light-year

6.02 × 1023 particles = 1 mole(602 000 000 000 000 000 000 000)

Sackheim’s Chemistry: Chapter 5

Mole (1)

• 1 mole = 6.02 × 1023 particles = Avogadro’s number (NA)

• By definition (based on a hydrogen atom): “One mole of a molecule has a mass (in grams) equal to its molecular mass”

– 1 mole of N2 = 1 x 28 = 28 g(6.02 × 1023 particles )

– 2 mol of CO2 = 2 x 44 = 88 g(12.04 × 1023 particles)

– 270 g of C6H12O6 = 270 / 180 = 1.5 mole (9,03 × 1023 particles)

Sackheim’s Chemistry: Chapter 5

N2

CO2

C6H12O6

(glucose)

Mole (2)

V: molar mass

x molar mass

GRAMS MOLES

Summary

Compounds

Ioniccompounds

Ionic bondingTransfer electronsEmpirical formula

Molecular compounds

polar and apolar

Covalent bondingShare electrons

Molecular formula

The End

Test your memory

A. True or False1. The electron-dot structure is also called Lewis structure2. Sharing valence electrons give rise to ionic compounds3. Hydrogen bonds are the reason for the remarkable properties of water4. A molecular formula represents the relative number of atoms 5. One mole of a molecule has a mass (in g) equal to its molecular mass

B. Multiple choice1. Important cation in our body are

a) Na+ and K+

; b) Cl- and O2-; c) H+ and Mg2+

2. What is the cause of ionic bondinga) Hydrogen bonding; b) Electron pairs; c) Electrostatic attraction

3. What is the oxidation number of P in P2O5

a) 4; b) 5; c) 6