Download - IB Chemistry: Topic 4: bonding
BondingTopic 4
Describe the ionic bond
The ionic bond
• Electrostatic attraction between oppositely charged ions.
• Elements in groups 1-7 (Analogy). • Transition elements can form more than
one ion (Fe+2, Fe+3). • Some compounds exist as ions
(Polyatomic ions).
Ionic bond formation• Ionization process. Energy
NaCl
Metal atom
Non-metal atom
Na+ Cl-
Electrostatic attraction Sodium chloride
In order to form an ionic compound
1. Position in the Periodic Table !• DOWN A GROUP, metals tend to lose
electrons. • UP A GROUP, non-metals tend to gain
electrons. • So, ionic bonds usually are formed
between atoms far from each other.
2. Electronegativity !• If the difference in electronegativity equals to 1.8
or higher than 1.8, the bond is ionic. !
• Data Booklet. Na2O MgO Al2O3 SiO2 P2O5
Lattice structures
• 3D structures. !
• Lattice enthalpy. !
• Geometry depends on size of ions. !
• Coordination number (NaCl is 6).
• Ionic structures http://www.chemguide.co.uk/atoms/structures/ionicstruct.html#top
!• Jmol: http://www.chemeddl.org/resources/
models360/solids.php#nacl
Practice
1. Solve some problems in pages 112 and 114. !
2. Class will be divided in 4 groups; each one will build and describe an ionic molecule. Once they are built, the class will discuss them and order them in increasing ionic character. !
3. HW #2: Solve problems on Edmodo.
Covalent bonds
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf
Lewis structure
• Represents the valence shell. !
• Ethane, hydroxide ion, ammonium, ethyne, CF3Cl.
!• Incomplete or expanded octate. BeCl2 and BF3.
They tend to form dative bonds (CO).
Strength of a bond
• What affects the strength? !
• Electrons can spend more time in the neighbouring atom.
!Polar bonds (assymetrical bond). Higher than 0 and smaller than 1.8 Non-polar = 0
VSEPR theory
• Valence Shell Electron Pair Repulsion. !
• Deduce geometry. !
• Importance. !
• Negative charge center.
VSEPR theory
• http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom3s2_7.swf
Shapes
!!http://phet.colorado.edu/en/simulation/
molecule-shapes
Polarity based on shape
• Net pull = 0. Non-polar • Net pull greater than 0. Polar !
CCl4 CH3Cl
H2O
Polarity based on shape
• http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom4s2_7.swf
Allotropes
http://www.chemeddl.org/resources/models360/solids.php#diamond
Diamond Graphite Fullerene•Repeated sequence of tetrahedrals. •Hardest natural substance. •sp3 C-C. •Does not conduct
•Hexagon parallel layers. •sp2 C-C. •van der Waals´ forces between layers (weak). •Good conductor.
•12 pentagons and 20 hexagons. •sp2 C-C. •Sphere. •Semiconductor.
Si and SiO2
Si • Tetrahedral. • Giant (covalent) lattice. !
SiO2 • Quartz. • Giant covalent. • Each Si attached to 4 O, and each O attached
to 2 Si. !http://www.chemeddl.org/resources/models360/
solids.php#quartz
Shapes of molecules and ions
Five negative charges
• Triangular bipyramidal.
Five negative charges
• One one-bonding pair. • Seesaw. • 180, 117.
Five negative charges
• Two non-bonding pairs. • T-shaped. • 90,180.
Five negative charges
• Three non-bonding pairs. • 180. • Linear. • Triiodide ion
Six negative charges
• Octahedral. • 90.
Six negative charges
• One non-bonding pair. • Square pyramidal. • 180, 90.
Six negative charges
• Two non-bonding pair. • Square planar. • 180.
HybridizationSigma bonds (simple) and Pi bonds (double-triple) !• http://www.mhhe.com/physsci/chemistry/
essentialchemistry/flash/hybrv18.swf !Hybridizations and geometry !• http://www.mhhe.com/physsci/chemistry/
animations/chang_7e_esp/bom5s2_6.swf
Intermolecular forces
• van der Waals’ forces Non-polar molecules. Temporary dipole. Induced dipole. Increases as size increases.
Intermolecular forces
• Dipole-dipole attraction Polar molecules have permanent dipole. When two molecules meet (same) a dipole-dipole attraction occurs.
Intermolecular forces
• Hydrogen bonds Hydrogens HAS to be attached to O, F or N.
Quick question
Which compound will have the highest boiling point, Water or Hydrofluoric acid?
!
WATER
Metallic bonding
• Electrons are delocalized (current). • The remaining cations form a lattice. “Lattice metal cations in a sea of delocalized electrons”.
• Melleability: shaped. !!
!• Ductility: Threads.
Physical properties
1. Solubility • How easy can a solute disperse a
solvent. • Polar dissolves polar. • H-bonds are also responsible. !2. Melting-boiling point • Ionic compounds tend to have high
melting points because of the lattice.
3. Electrical conductivity !• Depends on movile ions. • Covalent compounds do not conduct
electricity, except some, like HCl (Electronegativity difference = 1.2)
THANK YOU FOR YOUR ATTENTION