chemphys unit 4: chemical bonding
TRANSCRIPT
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