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Chemical Bond• A bond results from the attraction of nuclei
for electrons– All atoms trying to achieve a stable octet
• IN OTHER WORDS– the p+ in one nucleus are attracted to the e- of
another atom• Electronegativity
Two Major Types of Bonding
• Ionic Bonding – forms ionic compounds– transfer of e-
• Covalent Bonding– forms molecules– sharing e-
One minor type of bonding• Metallic bonding
– Occurs between like atoms of a metal in the free state
– Valence e- are mobile (move freely among all metal atoms)
– Positive ions in a sea of electrons
• Metallic characteristics– High mp temps, ductile, malleable, shiny– Hard substances– Good conductors of heat and electricity as (s) and (l)
It’s the mobile electrons that enable me-tals to
conduct electricity!!!!!!
IONic Bonding
• electrons are transferred between valence shells of atoms
• ionic compounds are made of ions
• ionic compounds are called Salts or Crystals
NOT MOLECULES
IONic bonding• Always formed between metals and
non-metals
[METALS ]+ [NON-METALS ]-
Lost e-Gained e-
• hard solid @ 22oC• high mp temperatures• nonconductors of electricity in solid
phase• good conductors in liquid phase or
dissolved in water (aq)
SALTS Crystals
Properties of Ionic Compounds
Covalent Bonding• Pairs of e- are shared
between non-metal atoms• electronegativity difference < 2.0 • forms polyatomic ions
molecules
Properties of Molecular Substances
• Low m.p. temp and b.p. temps• relatively soft solids as compared
to ionic compounds• nonconductors of electricity in any
phase
Covalent bonding
Covalent, Ionic, metallic bonding?
• NO2
• sodiumhydride
• Hg• H2S• sulfate
• NH4+
• Aluminum phosphate
• KH• KCl • HF
• CO• Co
Also study your
characteristics!
Drawing ionic compounds using Lewis Dot Structures
• Symbol represents the KERNEL of the atom (nucleus and inner e-)
• dots represent valence e-
NaCl• This is the finished Lewis Dot Structure
[Na]+ [ Cl ]-How did we get here?
• Step 1 after checking that it is IONIC– Determine which atom will be the +ion– Determine which atom will be the - ion
• Step 2– Write the symbol for the + ion first.
• NO DOTS
– Draw the e- dot diagram for the – ion• COMPLETE outer shell
• Step 3– Enclose both in brackets and show each charge
Draw the Lewis Diagrams• LiF• MgO• CaCl2
• K2S
Drawing molecules using Lewis Dot Structures
• Symbol represents the KERNEL of the atom (nucleus and inner e-)
• dots represent valence e-
Always remember atoms are trying to complete their outer shell!
The number of electrons the atoms needs is the total number of bonds they can make.
Ex. … H? O? F? N? Cl? C? one two one three one four
Methane CH4
• This is the finished Lewis dot structure
How did we get here?
• Step 1– count total valence e- involved
• Step 2– connect the central atom (usually the first in
the formula) to the others with single bonds • Step 3
– complete valence shells of outer atoms• Step 4
– add any extra e- to central atom
IF the central atom has 8 valence e- surrounding it . . YOU’RE DONE!
Sometimes . . . • You only have two atoms, so there is no
central atom, but follow the same rules. • Check & Share to make sure all the
atoms are “happy”.
Cl2 Br2 H2 O2 N2 HCl
• DOUBLE bond – atoms that share two e- pairs (4 e-)
O O• TRIPLE bond
– atoms that share three e- pairs (6 e-)
N N
Draw Lewis Dot StructuresYou may represent valence electrons
from different atoms with the following symbols x, ,
CO2
NH3
Draw the Lewis Dot Diagram for polyatomic ions
• Count all valence e- needed for covalent bonding
• Add or subtract other electrons based on the charge
REMEMBER! A positive charge means it LOST
electrons!!!!!
Draw Polyatomics• Ammonium• Sulfate
Types of Covalent Bonds• NON-Polar bonds
–Electrons shared evenly in the bond–E-neg difference is zero
Between identical atoms Diatomic molecules
Types of Covalent BondsPolar bond
–Electrons unevenly shared–E-neg difference greater than zero
but less than 2.0
closer to 2.0 more polar more “ionic character”
non-polar MOLECULES• Sometimes the bonds within a
molecule are polar and yet the molecule is non-polar because its shape is symmetrical. H
H
HH CDraw Lewis dot first andsee if equal on all sides
Polar molecules (a.k.a. Dipoles)
• Not equal on all sides–Polar bond between 2 atoms makes a
polar molecule–asymmetrical shape of molecule
H Cl δ-δ+
HHO
δ-
δ+
Water is asymmetricalδ+
Water is a bent molecule
OH H H H
Making sense of the polar non-polar thing
BONDS
Non-polar PolarIdentical Different
MOLECULES
Non-polar PolarSymmetrical Asymmetrical
IONIC bonds ….
Ionic bonds are so polar that the electrons are not shared but transferred between atoms forming ions!!!!!!
C. Johannesson
VSEPR Theory• Valence Shell Electron Pair Repulsion
Theory
• Electron pairs orient themselves in order to minimize repulsive forces.
C. Johannesson
VSEPR Theory• Types of e- Pairs
– Bonding pairs - form bonds– Lone pairs - nonbonding e-
Lone pairs repel more strongly than
bonding pairs!!!
4 Shapes of molecules
1. Linear (straight line)Ball and stick model
Space filling model
2. BentBall and stick model
Space filling model
3.Trigonal pyramidBall and stick model
Space filling model
4.TetrahedralBall and stick model
Space filling model
• Attractions between molecules– van der Waals forces
• Weak attractive forces between non-polar molecules
– Hydrogen “bonding”• Strong attraction
between special polar molecules
Intermolecular attractions
van der Waals• Non-polar molecules can exist in liquid
and solid phases because van der Waals forces keep the
molecules attracted to each other
• Exist between CO2, CH4, CCl4, CF4, diatomics and monoatomics
van der Waals periodicity• increase with molecular mass.
• increase with closer distance between molecules– Decreases when particles are farther away
Hydrogen “Bonding”• Strong polar
attraction– Like magnets
• Occurs ONLY between H of one molecule and N, O, F of another
H “bond”
H is shared between
2 atoms of OXYGEN or
2 atoms of NITROGEN or
2 atoms of FLUORINE
Of 2
different molecules
Why does H “bonding” occur?
• Nitrogen, Oxygen and Fluorine – small atoms with strong nuclear charges
• powerful atoms– very high electronegativities
Intermolecular forces dictate chemical properties
• Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.
Which substance has the highest boiling point?
• HF• NH3
• H2O
• WHY?
Fluorine has the highest e-neg, SO HF will experience the strongest H bonding and ∴ needs the most energy to weaken the i.m.f. and boil
The End