Chemical BONDING. Chemical Bond A bond results from the attraction of nuclei for electrons –All...
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Transcript of Chemical BONDING. Chemical Bond A bond results from the attraction of nuclei for electrons –All...
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
Breaking Bonds
• Endothermic reaction– energy must be put into the bond in order
to break itENERGY Reactants
Products
Energy Absorbed
Bond Strength• Strong, STABLE bonds require lots of
energy to be formed or broken
• weak bonds require little E
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)
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-
IONic Bonding• Electronegativity difference > 2.0
– Look up e-neg of the atoms in the bond and subtract
NaCl
CaCl2
• Compounds with polyatomic ionsNaNO3
• hard solid @ 22oC
• high mp temperatures
• nonconductors of electricity in solid phase
• good conductors in liquid phase or dissolved in water (aq)
SALTSCrystals
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-
• 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
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
• 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 Structures
You 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!!!!!
Types of CovalentCovalent BondsBonds• NON-Polar bonds
– Electrons shared evenly in the bond
– E-neg difference is zero
Between identical atomsDiatomic 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”
Place these molecules in order of increasing bond polarity
which is least and which is most?
• HCl
• CH4
• CO2
• NH3
• N2
• HF
a.k.a. “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
W - A - T - E - Ras bent as it can be!
Water’s polar MOLECULE!Water’s polar MOLECULE!
The H is positive The O is not - not - not - not
Making sense of the polar non-polar thing
BONDS
Non-polar Polar
Identical 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!!!!!!
• 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.
– Greater van der Waals force? • F2 Cl2 Br2 I2
• 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”
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 Unusual Properties of Water
• Unusually high boiling point
• Compared to other compounds in Group 16
H2O(s) is less dense than H2O(l)
• The hydrogen bonding in water(l) molecules is random. The molecules are closely packed.
• The hydrogen bonding in water(s) molecules has a specific open lattice pattern. The molecules are farther apart.