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