chemphys unit 4: chemical bonding
TRANSCRIPT
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Chemistry & Physics
UNIT 4: CHEMICAL BONDING
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Chemistry
Periodic table
Matter
Atoms
Chemical bonding
Chemical reaction
Electrolytes
Hydrocarbons
Organic chemistry
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Today
• Molecules• Chemical bonding
– Ionic bonding– Covalent bonding– Hydrogen bonding
• Formulas• Chemical calculations
– Oxidation number– Molar mass– Mole
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Chemical bonds
COVALENT BONDING
IONIC BONDING
HYDROGEN BONDING
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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
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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
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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
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Ion formation
Sackheim’s Chemistry: Chapter 4
• Formation of ions (stable)– Metals: lose electrons– Nonmetals: gain electrons
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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
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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
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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
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Ionic bonding (2)
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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
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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
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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”
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Nonpolar and polar bonds (2)
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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
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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
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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
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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
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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
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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
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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
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Chemical calculations
COMPOSITION
MOLES
MOLECULAR MASS
OXIDATION STATE
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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
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Calculating oxidation number
Sackheim’s Chemistry: Chapter 6
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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
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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
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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 %
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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
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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)
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Mole (2)
V: molar mass
x molar mass
GRAMS MOLES
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Summary
Compounds
Ioniccompounds
Ionic bondingTransfer electronsEmpirical formula
Molecular compounds
polar and apolar
Covalent bondingShare electrons
Molecular formula
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The End
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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