Post on 18-Jan-2016
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back!
DefinitionsIon
an atom that has gained or lost one or more electrons
Cationa positively charged ion
Aniona negatively charged ion
e-
e-e-
e-e-
1s
2s
2p
3s
3p
Ener
gyEnergy Level Diagram
Sodium
e- e- e- e- e-
e- e-
It could GAIN seven electrons to become more stable. Or…
Or it could LOSE one electron to become more stable.
Ion Na+
e- e- e- e- e- e-
All physical systems
tends towards a configurat
ion of lowest energy
Sodium will LOSE
an electro
n.
e-
e-e-
e-e-
1s
2s
2p
3s
3p
Ener
gyEnergy Level Diagram
e- e- e- e- e-
ChlorineIt could gain ONE electron to
become more stable. Or…
Or it could lose SEVEN electrons to become more stable.
e-e-
e-e- e-e- e- e-
e-
e-e-
e-e-
1s
2s
2p
3s
3p
Ener
gyEnergy Level Diagram
e- e- e- e- e-
Chlorine
Gaining an electron would require the least amount of
energy!
e-e-
e-e- e-e- e- e-
Ion Cl-
Valence electronsElectrons in the outermost
s and p orbitals
These are the most reactive
e-
e-e-
e-e-
1s
2s
2p
3s
3p
Ener
gyEnergy Level Diagram
Sodium
e- e- e- e- e-
e-
Has only ONE electron in its outermost s and p orbitals.
Therefore, it has one valence electron.
e-
e-e-
e-e-
1s
2s
2p
3s
3p
Ener
gyEnergy Level Diagram
e- e- e- e- e-
Chlorine
e-e-
e-e- e-e- e-
Has SEVEN electrons in its outermost s and p orbitals.
Therefore, it has seven valence electrons.
Lewis dot
structures
An easier way to draw the valence electrons is through…
Sometimes atoms get together and one or more electrons jumps
from one atom to another…
…this causes both atoms to have opposite charges (ions)…
…which then causes these ions to be attracted to each other.
Ionic Bond
For example…
Chlorine has a greater attraction for electrons than
Sodium
But why?Electronegativity / Chlorine = catcher
Ionic bondsOccur between metals and nonmetals
Like Sodium and Chlorineor
Potassium and Fluorine
In an ionic bond, electrons are first lost or gained, resulting in the formation of ions.
FK
FK
FK
FK
FK
FK
FK+_
Potassium (K+) ion[cation]
Fluoride (F-) ion[anion]
An ionic bond forms from the attractionbetween the positive K+ ion
and the negative F- ion
FK+_
An ionic bond forms from the attractionbetween the positive K+ ion
and the negative F- ion
The compound potassium fluoride (KF) consists of potassium (K+) ions
and fluoride (F-) ions
Ionic Bonds Properties of Ionic
Compounds
Electrons are exchanged
Ions are formed
Ions “stick together” magnetically to form
compound
Formed between metals and nonmetals
Electronegativity difference >1.7
Cation + Anion = “salt”
Forms crystals (ordered arrangements of ions)
Conduct electricity when dissolved or melted
High melting/boiling points
Hard and brittle
Rarely burn
Formation is always exothermic
Covalent BondsProperties of Covalent
Compounds
Electrons are shared
No ions are formed
Formed between two nonmetals
Electronegativity difference is
minimal
Low melting and boiling points
Typically soft and squishy
Usually do not dissolve in water as well as ionic
compounds
Don’t conduct electricity
Sometimes burn
Covalent bondsOccur between two nonmetals
Like Hydrogen and Chlorineor
Chlorine and Chlorine
In covalent bonding, atoms still want to achieve the lowest energy level possible (which means filling up all eight of their
valence seats.)
But rather than losing or gaining electrons, atoms now SHARE an
electron pair.
All physical systems
tends towards a configurat
ion of lowest energy
Covalent bonds
attempt to fill up all eight of
their valence seats…
Just like noble
gases!
Cl2
Chlorine forms
acovalent bond
withitself
ClClHowwilltwo
chlorine
atomsreact?
Each chlorine atom wants to gain one
electron to fill all of its seats.
ClCl
Cl Cl
Cl Cl
Cl Cl
Cl ClThe octet is achieved byeach atom sharing the
electron pair in the middle.
Cl ClFull 8 seats
(octet)Full 8 seats
(octet)
Cl ClThe octet is achieved byeach atom sharing the
electron pair in the middle.
Cl ClThis is the bonding pair
It is a single bonding pair
It is called a SINGLE BOND
Single bonds are abbreviated with a dash
Cl ClThis is the bonding pair
It is a single bonding pair
It is called a SINGLE BOND
Single bonds are abbreviated with a dash
Cl Cl
circle the electrons foreach atom that completestheir octets
Single bonds are abbreviated with a dash
Cl Cl
circle the electrons foreach atom that completestheir octets
This is the chlorine molecule
Cl2
Remember: Covalent bonds occur between two nonmetals!
Covalent bonds
You know this…
…and this.But you need to learn this!
O2Oxygen can also form a covalent
bond with itself.
But it needs to form two bonds since it is in Group 6A.
How can this be done?
OO
OOEach atom has two unpaired electrons
OO
OO
OO
OO
OOBoth electron pairs are shared.
6 valence electronsplus 2 shared electrons
= full octet
OO
OO6 valence electrons
plus 2 shared electrons= full octet
Two bonding pairs,
OO
making a double bond.
OO =For convenience, the double bond
can be shown as two dashes.
OO
OO =This is the oxygen molecule,
O2
Covalent bondsPolar Covalent Bond
• Shared electrons spend more time closer to one of the bonding atoms
• For example – H20
Non-Polar Covalent Bond• Shared electrons do not spend more
time closer to one of the bonding atoms• For example – 02
Two kinds…
Polar covalent bondsShared electrons spend more time closer to
one of the bonding atoms
Oxygen
HHThe
probability distribution for shared electrons.
The electrons
spend more time
near the oxygen atom.
How can you tell if you have a polar or non-polar
covalent bond?ELECTRONEGATIVI
TYElectronegativity is the power of an atom to attract electrons
The higher the value, the more electronegative the element
Remember probability distribution?
Non-polar covalent
bondsShared electrons do not spend more time closer to one of the bonding atoms
Oxygen
The probability distribution for shared electrons is shared by
both.
Oxygen
Polar covalent bond
Non-polar covalent bond
If the electronegativity difference between the two
nonmetals is 0.3-1.7
If the electronegativity difference between the two nonmetals is less than 0.3
ReviewIonic bond• Between a metal and nonmetal• Electrons are lost/gained and the
resulting change in charge attracts the ions together
Covalent bond• Between two nonmetals• Electrons are shared between the atoms• Polar/Non-polar• Ruled by electronegativity