Bonding
Why do Atoms Bond?
• Atoms bond when their valence electrons interact
• Generally, atoms join to form bonds so that each
atom has a full outermost energy level.
• Examples – Draw the Bohr model for:
Ne
F
O
Li
2 8
Full outer
level
2 7
Needs 1 e
2 6
Needs 2 e
2 1
Give away
1e
Ionic Bonds
• Formed when atoms TRANSFER electrons
• This causes two oppositely charged ions to
form
• What is an ion? It is an atom with a charge
• Both ions that form have a filled outermost
energy level
• The result is a POSITIVE ion and a
NEGATIVE ion.
Calculating Charges of Ions
• Sodium normally has 11 electrons, 1 valence
electron. It gives it away. It still has 11 protons,
but now has 10 electrons.
+11
-10
+1 charge
• If an atom loses an electron, its charge is +1
• If an atom loses two electrons, its charge is +2
• If an atom gains an electron, its charge is –1
• If an atom gains two electrons, its charge is -2
Examples: Lithium & Fluorine
Li
First, draw the Bohr Model
+1
F
+3
+9
-2
-10
-1
Lithium has an extra electron, fluorine needs one more
Lithium gives its valence electron to Fluorine
Li now has a +1 charge. F now has a -1 charge.
Oppositely charged ions attract each other and form an
ionic bond.
Ionic Bonding Animation (NaCl)
•
The Dog Bone Analogy
Taken from http://ithacasciencezone.com/chemzone/lessons/03bonding/dogbonds.htm
• Ionic bonding can be best imagined as
one big greedy dog steeling the other
dog's bone.
More Facts About Ionic Bonds
• When melted or dissolved in water, ionic
compounds conduct electricity
• Elements in ionic bonds form COMPOUNDS
from a METAL and a NONMETAL
• How do you determine metals vs nonmetals?
– Look on your periodic table…there is a little stair
step that divides metals from nonmetals
– Elements to the right of this line (including
Hydrogen!) are nonmetals
– Elements to the left of this line are metals
Reactivity of Metals
• Reactivity lab – think back to the reactivity lab…which
was more reactive: Al or Mg?
• Mg was…it had fewer valence electrons.
• In the case of a METAL, fewer valence electrons = more
reactive…but WHY?
– Metals are trying to get rid of their electrons.
– Electrons are attracted to protons. Farther to the left on the
periodic table, elements have fewer protons.
– Fewer protons, less attraction, easier to get rid of electrons
• Predict which is more reactive, Na or K.
• K…it has more energy levels.
– The farther an electrons is from the nucleus, the easier it is to
give away.
• Nonmetals are OPPOSITE from metals
Covalent Bonds
• Atoms joined by covalent bonds SHARE
electrons
• Covalent bonds form MOLECULES
• Made from 2 or more NONMETALS
• In the case of covalent bonds, atoms don’t
transfer electrons because each needs to gain
electrons
Examples of Covalent Bonds
F2
Both need 1 electron so they share one electron each
Covalent Bonding Animation (Cl2)
•
Non-Polar Covalent Bonds
• When both atoms are the
same, the electron is
shared EQUALLY
• Atoms may share more
than one pair of electrons
• Examples: O2 or Cl2
The Dog Bone Analogy
• Covalent bonds can be thought of as two or
more dogs with equal attraction to the
bones. Since the dogs (atoms) are identical,
then the dogs share the pairs of available bones
evenly.
Polar Covalent Bonds
• When two UNLIKE atoms share
electrons, the electrons are NOT
shared equally
• Electrons are attracted to elements
that are located farther to the right
and closer to the top of the
periodic table
• The occurs because:
– Farther to the right has more protons
– Closer to the top has fewer energy
level
• Example: CO2
The Dog Bone Analogy
• These bonds can be thought of as two or more
dogs that have different desire for bones. The
bigger dog has more strength to possess a larger
portion of the bones. Sharing still takes place
but is an uneven sharing.
Polyatomic Bonds
• Two or more covalently bonded atoms form an ion
because they have either gained or lost electrons
• Examples (you do not have to memorize these).
• Hydroxide
• Carbonate
• Sulfate
• Nitrate
• Nitrite
• Phosphate
• Hydrogen Sulfate
• Cyanide
OHCO32SO42NO3NO2PO43HSO4CN-
Review Questions
• In what type of bond are electrons shared equally?
– Nonpolar covalent
• In what type of bond are electrons transferred?
– ionic
• Determine if the following compounds/molecules are
likely to have ionic or covalent bonds:
– MgO
• Ionic (a metal and a nonmetal)
– SrCl2
• Ionic (a metal and a nonmetal)
– O3
• Covalent (nonpolar – all the same nonmetal)
– CH4O
• Covalent (polar – different nonmetals)
• Explain why electrons are shared equally in ozone, O3,
and unequally in carbon dioxide, CO2.