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CHEMICAL BONDING•COVALENT BONDS• IONIC BONDS•METALLIC BONDS
Reflection (pg 62)
• What is a metallic bond?• Compare/contrast it to ionic/covalent bond
Metallic Bonds
• How atoms are held together in the solid.
• Metals hold onto there valence electrons very weakly.
• Think of them as positive ions floating in a sea of electrons.
Sea of Electrons
+ + + ++ + + +
+ + + +
• Electrons are free to move through the solid.
• Metals conduct electricity.
Characteristic of Metallic Bonds
• High electrical and thermal conductivity
• Malleable, ductile, high luster.
• Great amount of heat needed to break these bonds.
IONIC BONDING
When an atom of a nonmetaltakes one or more electrons
from an atom of a metalso both atoms end up with
eight valence electrons
IONIC BONDING
IS THE COMPOUND AN IONIC COMPOUND?
METAL NONMETAL
SUBSCRIPTS
IONIC BOND FORMATION
IONIC BONDING
ION – any atom with more orless electrons that it is
supposed to have*
*Remember that the number of electronsis supposed to be equal to the number ofProtons if the atom has a neutral charge
IONIC BONDING
Metals will tend to lose electrons and become
POSITIVE CATIONS
Normal sodium atom loses one electron to become sodium ion
Na+1 is called a sodium ion
The +1 symbol means it
has lost one electron
IONIC BONDING
IONIC BONDING
Nonmetals will tend to gain electrons and become
NEGATIVE ANIONS
Normal chlorine atom gains an electron to become a chloride ion
Cl-1 is called a chloride ion
The -1 symbol means it
has gained one electron
IONIC BONDING
Properties of Ionic Compounds• Hard, brittle solids.• Strongest bond.• Most dissolve in water• Conduct electricity when
dissolved in water.• High melting/ boiling points-
because of strong forces between ions.
Crystalline structure
+
+
+ +
+
+
++
+
--
--
- --
--
The POSITIVE CATIONS stick to the
NEGATIVE ANIONS, like
a magnet.
COVALENT BOND FORMATION
When one nonmetal shares one or more electrons with an atom of another nonmetal so both atoms end up with eight valence electrons
COVALENT BONDING
IS THE COMPOUND A COVALENT COMPOUND?
NONMETAL NONMETAL
YES since it is made of only nonmetal elements
Polar Bonds• When two different atoms are connected,
the atoms may not be shared equally.• This is a polar covalent bond.
pages.uoregon.edu
Nonpolar Bonds• When the atoms in a bond are the same, the
electrons are shared equally.• This is a nonpolar covalent bond.
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Characteristics of Covalent Bonds• Represented by Lewis structures• Strong bond but weaker than Ionic
bonds• Low melting points & boiling points• Most do not dissolve in water• Do not conduct electricity.• Usually in a gas state at room
temperature
Covalent bonds• Monatomic: contains one atom• Diatomic: contains two atoms
BrINClHOFBromine (Br2), Iodine (I2), Nitrogen (N2), Chlorine (Cl2), Hydrogen (H2), Oxygen (O2), Fluorine (F2)
You must have these memorized!!!!• Polyatomic: contains more than one atom.
Octet Rule• Octet rule: atoms tend to gain, lose, or share
electrons until they are surrounded by 8 valence electrons (4 electron pairs).
• Exceptions:• Hydrogen forms bonds in which it is surrounded
by only two electrons.• Boron tends to form bonds in which it is
surrounded by 6 electrons.• Main group elements in period 3 and up can form
bonds with expanded valance shells.
Lewis structure rules• 1.Write the element symbol. Around this
draw dots—one for each valence electron.• 2. The dots sould be spread over four sides.
Dots are not paired until all sides have at least one dot.
• 3. It does not matter on which side dots are placed. Example- Hydrogen can be drawn in four ways:
H H H H
Lewis structure rules
• 4. The number of valence electrons is equal to the group number for groups 1 and 2. In groups 13 to 18, subtract 10 and that is the number of valence electrons.
Multiple bonds in Lewis Structures
• Molecules containing carbon (C), nitrogen (N), and oxygen (O) may form multiple bonds.
• The need for multiple bonds becomes obvious if there are not enough valence electrons to complete octets by adding unshared electron pairs.
Double bonds• Produced by sharing two pairs of electrons
between two atoms.
C C CCH
H
H
HH
H
H
H
Triple Bonds• Produced by sharing three pairs of electrons
between two atoms.
N
MOLECULAR SHAPES
OFCOVALENT
COMPOUNDS
VSepR tHEORY
What Vsepr means
Since electrons do not like each other, because of their negative charges, they orient themselves as far apart as possible, from each other.
This leads to molecules having specific shapes.
Things to remember
•Atoms bond to form an Octet (8 outer electrons/full outer energy level)
•Do NOT forget all electron pairs, including unshared electron pairs!!!
Linear
• The central atom is represented by A and the atoms bonded to the central atom are B.
• The molecule AB2 is linear
• Bond Angle = 180°
EXAMPLE:
BeF2
Trigonal Planar
• The molecule AB3 makes an equilateral triangle.
• Bond Angle = 120°
EXAMPLE:
GaF3
Tetrahedral
• The molecule AB4 makes the shape of a tetrahedral (kind of looks like a pyramid).
• Bond Angle = 109.5°
EXAMPLE:
CH4