Download 4. bonding - New Hartford Central Schools

Formula Writing
oxidation number-number assigned to keep track of electron gain or loss
lose electron
cation
METALS
-
+
gain electron
anion
(nonmetals)
cation is written first anion is second
positive ion first negative ion second
Polyatomic Compounds
Binary Compound
Compound made of 3 or more
elements
Compound made of only two
elements
(Usually metal with nonmetal)
Use Criss-Cross
(Usually table E, polyatomic ions)
Definition
Use Criss-Cross
Binary Compound
Second element name ends
in “-ide”
Definition
Aluminum Sulfide
1. Look up symbol for the element on
Table S
Al
S
2. Write the oxidation number, (which
are found on the Periodic Table, above
each symbols as a superscript):
Al +3
S-2
3. Crisscross the oxidation numbers and
omit the charge signs. Write the numbers
below the symbols as subscripts.
Al2S3
Note: The crisscrossing of the oxidation
numbers conserves the charge.
The sum of the oxidation numbers of all
of the atoms in a compound is always
zero.
4. When each element has the same
oxidation number, these numbers are
dropped and the formula is correct as
written in step 1.
Polyatomic Compounds
Second element can end in
-”ate” -”ite” -”ium”
ONLY -”ide’s”: “peroxide, hydroxide,
cyanide
Aluminum Sulfate
1. Look up symbol for the element on Table S;
polyatomic ion on Table E
Al SO4
2. Write the oxidation numbers, which are
found on the Periodic Table, above each
symbols as a superscript:
Al +3
SO4-2
3.Place the polyatomic ion in parentheses
Crisscross the oxidation numbers and omit
the charge signs. Write the numbers below the
symbols as subscripts.
Al2(SO4)3
The sum of the oxidation numbers of all of the
atoms in a compound is always zero.
4. When each element has the same oxidation
number, these numbers are dropped and the
formula is correct as written in step 1.
Sodium Sulfide
Na
-ide on PT
-ate on Table E
S 2-
+1
Na
Sodium Sulfate
+1
Na2S
S
2-
Na
+1
SO4
2-
***MUST use parentheses hereif it’s more than one!***
Na2 SO4
Naming Compounds
Ionic compounds
Naming Binary Compounds
1. The element with the positive
ionic charge is written first.
2. The second word is formed by
changing the ending of the name
of the element to “ide”. Example
bromine becomes bromide.
Metals usually have positive ionic
charges
Nonmetals (when combined with
metals) have negative charges.
NaCl
Polyatomic Ions
Look up the name of the polyatomic ion
on chart table E
When polyatomic ion is second
1. write the name of the first element
2. write the name of the polyatomic ion
Na2SO4
Sodium sulfate
If polyatomic ion first
1. look up ion name
2. follow ending for binary compounds
NH4Cl
sodium chlorine
ammonium chlorine
sodium chloride
ammonium chloride
Naming & Writing
Compounds
Elements with more than one positive oxidation number (Transition Metals)
(This is called the Stock System)
When the oxidation number varies we us a Roman numeral in parentheses to
indicate the charge. Roman number is used for the positive element only!!!
(I, II, III, IV, V, VI, VII, VIII, IX, X)
FeO Iron (II) oxide
Fe2O3 Iron(III) oxide
Alternative method for compounds
**TRANSITION
METALS!!!!!
ALL NON METALS ONLY!!!
We can also use prefix to indicate the number of each element
mon 1, di 2, tri 3, tetra 4, penta 5, hexa 6, hepta 7, octa 8, non 9, deca 10
***No criss cross***
If the first element is 1, don’t write mono ALWAYS prefix for 2nd
Carbon monoxide
CO
dinitrogen trioxide
N2O3
Chemical Bonding
Chemical bonds are the forces that hold atoms together in a
compound.
• when atoms bond they release energy and become more stable
Ionic
Covalent
Metallic
Ionic Bonds
Metal/nonmetal
e- is transferred from
the metal to the
nonmetal
EN difference greater
than 1.7
Greater the EN
difference, greater the
ionic character
Transfer e-
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Ionic Solid
hard
crystalline
high melting and boiling points
do not conduct electricity in the solid state
do conduct electricity in the molten (liquid) or
aqueous state (aq)-electrolyte (ions)
NaCl
Covalent Bond Share e
2 nonmetals
Nonpolar
Polar
Same nonmetals
Different nonmetals
Share the electrons
equally
Share the electrons
unequally
Difference of 0
Difference of
0.1-1.7
Cl2
H20
CO2
-
Coordinate
Moochers
one atom donates a
pair of electrons to
be share, the other
contributes none
NH4+
H3O+
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Molecular Substance
are brittle in the solid form
All 3 states of matter
are poor conducts of heat and
electricity
Low melting and boiling points
C6H12O6
Network Solid
Hard
crystalline
Are poor conductors of heat
and electricity
High melting boiling points
C-diamond
SiO2-quartz/sand
SiC
CO2
HCl
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Metallic Bonds Mobile e
-
metal
Metals
Electrons move freely
from one atom to
another.
“sea of mobile
electrons”
+ + + + + ++ + + + + + +
- - - - - - - -- - - - - - - - - - ++++++++++++
good conductors of
electricity and heat in
any state
malleable
ductile
high melting and high
boiling points
Venn diagram
Ionic
Covalent
Venn diagram
Ionic
Forms when one atom
donates electrons to another
Exist between ions
Holds ions together in an
ordered 3-d array, called an
ionic crystal
Typically exist between atoms on
opposite sides of the periodic table
Results from electrostatic
attraction between
opposite charges
Covalent
Are forces acting
between atoms to hold
them together
Forms when atoms share 2,4,6
electrons
Builds molecules
Can form when atoms
make contact
Either absorb or
release energy when
formed
Create new species with chemical and
physical properties unlike constituent
atoms
Form because atoms
want to have complete
outer shells
Can be polar or non-polar
Exist between neutral atoms
Forms when atoms that tend to
gain electrons come into contact
with one another
Generally form between atoms
in the upper right hand corner
of the periodic table
Lewis Dot Structure
Octet
Rule
molecules and ions need to have eight electrons in
their valance level as the result of bond formation
Hydrogen and helium want 2
Rules for drawing an atom.
Shows the number of valence electrons for an individual atom
Find the number of valence e
Put 2 on top
Put 1 on each side
double up
Ionic
Metal/nonmetal OR an ION (just choose half)!
Write the formula-tell how many of each atom you need
Metal:
Nonmetal:
no dots
8 dots
Aluminum bromide
positive charge
[ ]
negative charge
[ ]
Covalent
***MOLECULE!!!!!!!***
ALL non metals
1. Look at the formula- find the element that’s only 1. (ex. H2O- the O)
2. Draw it like the atom (Limo Bus)- look up valence e-’s on PT.
3.
Make sure electrons are in PAIRS!!!!
4.
Complete the octet rule for all non-central atoms.
5.
Check work.
** If it’s CARBON (C) …spread out the 4 electrons…
***Memorize the double and triple bonds. (O2, N2, CO2)
Shapes and Polarity of Molecules
(ALL NON-METALS!!!!)
Determining Polarity
Symmetrical non polar - opposite sides match
Cross test
Asymmetrical - polar opposite sides don’t match
+
** MUST be symmetrical in both directions to be considered NonPolar. “SNAP”
linear
Check symmetry
Definition
2 atoms connected
3 atoms in a line
1 central atom with 4
atoms around it
Check symmetry No unpaired e around central
atom
tetrahedral
pyramidal
Always polar
bent
Always polar
1 central atom with
3 atoms around the central
Atom
1 pair of e not shared
1 central atom, with 2 other
atoms off the central atom
2 pairs of e not shared
Ball and Stick Model
Example
HBr H Br
CO2 O C O
CH4 (non polar)H
CH3F (polar)
NH3
C
H
N
H
H2O
H
H
H
O
H
H
H
Shape
Intermolecular Forces
Are the forces that exist between individual molecules--weaker than a bond
Hydrogen Bonding
between molecules
containing
Hydrogen bonded with
F, O, N
small highly
electronegative
Dipole - Dipole
dipole - polar molecule
H-Br
Atom with the higher EN will
be negative.
between polar molecules
H-F **H-F
H-Br *****H-Br
Van der Waals
London Dispersion
between non polar
molecules
Diatomic elements
Noble gases
Organic-C
Force is stronger:
1. Closer they are
2. Heavier they are
CH4 ****CH4
Stronger the intermolecular force, higher the melting
and boiling point
Ionic > H-bond > Molecular (Covalent molecules)
Molecule- Ion Attraction
Ionic solids when placed in water dissociate ( separate)
due to the attraction of opposite charges
Polar and ionic
(aq)
NaCl (aq)
Na+
Cl
-