Chemistry & Physics UNIT 4 discusses key concepts in chemical bonding including: 1) Ionic bonding occurs through the transfer of electrons between atoms to form ions that are attracted via electrostatic forces. Covalent bonding involves the sharing of electron pairs between atoms. 2) Molecules are formed when two or more atoms combine via chemical bonds. Their formulas represent the elements present, with molecular formulas showing actual atom ratios. 3) Hydrogen bonding between water molecules gives rise to water's unique properties and ability to dissolve many substances. It also allows for the three-dimensional structures of proteins and DNA.

1. Chemistry & Physics
UNIT 4: CHEMICAL BONDING

2. Chemistry
Periodic table
Matter
Atoms
Chemical bonding
Chemical reaction
Electrolytes
Hydrocarbons
Organic chemistry

3. Today
• Molecules
• Chemical bonding
– Ionic bonding
– Covalent bonding
– Hydrogen bonding
• Formulas
• Chemical calculations
– Oxidation number
– Molar mass
– Mole

4. Chemical bonds
COVALENT BONDING
IONIC BONDING
HYDROGEN BONDING

5. 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

6. 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
coefficient
subscript

7. 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

8. Ion formation
Sackheim’s Chemistry: Chapter 4
• Formation of ions (stable)
– Metals: lose electrons
– Nonmetals: gain electrons

9. 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

10. Polyatomic ions
Formula Name
SO4
2- Sulfate
NO3
- Nitrate
PO4
3- Phosphate
CO3
2- Carbonate
OH- Hydroxide
HCO3
- Bicarbonate
NH4
+ Ammonium
Sackheim’s Chemistry: Chapter 4
Group of atoms acting as one ion

11. 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

12. Ionic bonding (2)

13. 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

14. 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

15. 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”

16. Nonpolar and polar bonds (2)

17. 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

18. 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

19. Water
EXPERIMENT 002
Title: Water Skin
Topic: Hydrogen bonding
1. Put the paperclip on water surface
2. Watch the result
3. Add two drops of soap detergent near
the paper clip
4. Watch the result

20. 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

21. 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

22. 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

23. 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 4
NH3

24. Chemical calculations
COMPOSITION
MOLES
MOLECULAR MASS
OXIDATION STATE

25. 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

26. Calculating oxidation number
Sackheim’s Chemistry: Chapter 6

27. 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

28. 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

29. Mass percentage
• Relative atomic mass (percentage) of the elements present in the
molecule
– C6H12O6: Glucose
%𝑪 =
𝒎𝒂𝒔𝒔 𝒐𝒇 𝑪 𝒊𝒏 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
𝒎𝒂𝒔𝒔 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
× 𝟏𝟎𝟎 =
𝟔 × 𝟏𝟐
𝟏𝟖𝟎
× 𝟏𝟎𝟎 = 𝟒𝟎%
%𝑯 =
𝒎𝒂𝒔𝒔 𝒐𝒇 𝑯 𝒊𝒏 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
𝒎𝒂𝒔𝒔 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
× 𝟏𝟎𝟎 =
𝟏𝟐 × 𝟏
𝟏𝟖𝟎
× 𝟏𝟎𝟎 = 𝟕%
%𝑶 =
𝒎𝒂𝒔𝒔 𝒐𝒇 𝑶 𝒊𝒏 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
𝒎𝒂𝒔𝒔 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆
× 𝟏𝟎𝟎 =
𝟔 × 𝟏𝟔
𝟏𝟖𝟎
× 𝟏𝟎𝟎 = 𝟓𝟑%
Sackheim’s Chemistry: Chapter 5
100 %

30. 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

31. 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)

32. Mole (2)
V: molar mass
x molar mass
GRAMS MOLES

33. Summary
Compounds
Ionic
compounds
Ionic bonding
Transfer electrons
Empirical formula
Molecular
compounds
polar and apolar
Covalent bonding
Share electrons
Molecular formula

34. The End

35. Test your memory
A. True or False
1. The electron-dot structure is also called Lewis structure
2. Sharing valence electrons give rise to ionic compounds
3. Hydrogen bonds are the reason for the remarkable properties of water
4. 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 choice
1. 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 bonding
a) Hydrogen bonding; b) Electron pairs; c) Electrostatic attraction
3. What is the oxidation number of P in P2O5
a) 4; b) 5; c) 6