Chemical Bond · Chemical Bond • A bond results from the attraction of nuclei for electrons –...
Transcript of Chemical Bond · Chemical Bond • A bond results from the attraction of nuclei for electrons –...
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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
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Two Major Types of Bonding
• Ionic Bonding – forms ionic compounds– transfer of e-
• Covalent Bonding– forms molecules– sharing e-
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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)
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It’s the mobile electrons that enable me-tals to
conduct electricity!!!!!!
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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
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IONic bonding• Always formed between metals and
non-metals
[METALS ]+ [NON-METALS ]-
Lost e-Gained e-
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• 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
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Covalent Bonding• Pairs of e- are shared
between non-metal atoms• electronegativity difference < 2.0 • forms polyatomic ions
molecules
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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
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Covalent, Ionic, metallic bonding?
• NO2
• sodiumhydride
• Hg• H2S• sulfate
• NH4+
• Aluminum phosphate
• KH• KCl • HF
• CO• Co
Also study your
characteristics!
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Drawing ionic compounds using Lewis Dot Structures
• Symbol represents the KERNEL of the atom (nucleus and inner e-)
• dots represent valence e-
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NaCl• This is the finished Lewis Dot Structure
[Na]+ [ Cl ]-How did we get here?
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• 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
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Draw the Lewis Diagrams• LiF• MgO• CaCl2
• K2S
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Drawing molecules using Lewis Dot Structures
• Symbol represents the KERNEL of the atom (nucleus and inner e-)
• dots represent valence e-
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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
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Methane CH4
• This is the finished Lewis dot structure
How did we get here?
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• 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!
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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
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• DOUBLE bond – atoms that share two e- pairs (4 e-)
O O• TRIPLE bond
– atoms that share three e- pairs (6 e-)
N N
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Draw Lewis Dot StructuresYou may represent valence electrons
from different atoms with the following symbols x, ,
CO2
NH3
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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!!!!!
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Draw Polyatomics• Ammonium• Sulfate
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Types of Covalent Bonds• NON-Polar bonds
–Electrons shared evenly in the bond–E-neg difference is zero
Between identical atoms Diatomic molecules
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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”
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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
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Polar molecules (a.k.a. Dipoles)
• Not equal on all sides–Polar bond between 2 atoms makes a
polar molecule–asymmetrical shape of molecule
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H Cl δ-δ+
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HHO
δ-
δ+
Water is asymmetricalδ+
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Water is a bent molecule
OH H H H
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Making sense of the polar non-polar thing
BONDS
Non-polar PolarIdentical Different
MOLECULES
Non-polar PolarSymmetrical Asymmetrical
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IONIC bonds ….
Ionic bonds are so polar that the electrons are not shared but transferred between atoms forming ions!!!!!!
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C. Johannesson
VSEPR Theory• Valence Shell Electron Pair Repulsion
Theory
• Electron pairs orient themselves in order to minimize repulsive forces.
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C. Johannesson
VSEPR Theory• Types of e- Pairs
– Bonding pairs - form bonds– Lone pairs - nonbonding e-
Lone pairs repel more strongly than
bonding pairs!!!
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4 Shapes of molecules
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1. Linear (straight line)Ball and stick model
Space filling model
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2. BentBall and stick model
Space filling model
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3.Trigonal pyramidBall and stick model
Space filling model
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4.TetrahedralBall and stick model
Space filling model
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• Attractions between molecules– van der Waals forces
• Weak attractive forces between non-polar molecules
– Hydrogen “bonding”• Strong attraction
between special polar molecules
Intermolecular attractions
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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
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van der Waals periodicity• increase with molecular mass.
• increase with closer distance between molecules– Decreases when particles are farther away
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Hydrogen “Bonding”• Strong polar
attraction– Like magnets
• Occurs ONLY between H of one molecule and N, O, F of another
H “bond”
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H is shared between
2 atoms of OXYGEN or
2 atoms of NITROGEN or
2 atoms of FLUORINE
Of 2
different molecules
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Why does H “bonding” occur?
• Nitrogen, Oxygen and Fluorine – small atoms with strong nuclear charges
• powerful atoms– very high electronegativities
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Intermolecular forces dictate chemical properties
• Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.
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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
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The End