Transcript Ionic Bonds PPT

Chapter 7
Ions
• Valence electrons are the electrons in the
highest occupied energy level of an
elements atoms.
– Valence electrons determine the chemical
properties
– THE HILL OF OXIDATION NUMBERS
Valence Electrons
• Group # shows the
# of Valence
Electrons!
• 1A = 1
• 2A = 2
• Etc..
• A bit of a review!
Octet
Rule
• In forming compounds, atoms tend to
gain or lose electrons in order to
achieve the electron configuration of a
noble gas!!!
Octet Rule = atoms tend to gain, lose or share electrons so
as to have 8 electrons
C would like to lose 4 electrons
N would like to Gain 3 electrons
O would like to Gain 2 electrons
Key Concept
• Metals form Cations
• Nonmetals form
Anions
Formation of Cations
• When an atom loses an electron it
produces a positively charged ion, or a
cation.
• .
Electron–Dot Structures for Ions
• Remove
electrons
for cations
Sodium
Atomic number 11
1s22s22p63s1
1 Valence electron
Na
Remove electron to form ion
Sodium Ion
Atomic number 11
1s22s22p63s0
Na+
Now has full shell with similar electronic configuration to Neon
--Stable noble gas configuration
Formation of Anions
• The gain of negatively
charged electrons by
a neutral atom
produces an anion.
Electron–Dot Structures for Ions
• Add
electrons
for anions
Chlorine
atomic number 17
1s22s22p63s23p5
7 Valence electrons
Cl
Add electron to form ion
Chloride ion
atomic number 17
1s22s22p63s23p6
8 Valence electrons
Cl
-
Now has full shell with similar electronic configuration to Argon
--Stable noble gas configuration
Lewis Dot Structures
The valence shell is the outermost shell of electrons of an atom.
Mg example
1s22s22p6 3s2
[Ne] 3s2
2 electrons in the valence Shell
Use dots to represent Valence Electrons
Mg
Electron-Dot Structures
• Valence electrons represented by dots
• Electron-dot symbols
– Examples: Na•, •Mg•, …
Ionic Bonds
• Compounds composed of
cations and anions are
called ionic compounds.
• Although they are
composed of ions, ionic
compounds are
electrically neutral.
The electrostatic forces that hold ions
Together in ionic compounds are
Called Ionic bonds.
Formula Units
• Shows the number of atoms in a
compound.
• Ionic compounds = Formula Units
Properties of Ionic Compounds
1. Most are crystalline
solids at room
temperature.
2. High melting points.
3. Conduct electricity
when melted or
dissolved in water.
• A formula unit is the
lowest whole-number
ratio of ions in an
ionic compound.
• For NaCl the ratio of
the ions is 1:1 (one
Na+ to one Cl-)
• What is the formula unit
for Magnesium Chloride?
Practice, Practice, Practice
• Use the criss cross
method to determine
formulas of the ionic
compounds formed
when
• 1. potassium reacts
with iodine.
• 2. Aluminum reacts
with oxygen.
Practice, Practice
•
1.
2.
3.
4.
Write the formulas
for each compound.
Barium chloride
Lithium oxide
Magnesium oxide
Calcium flouride
7.3 Bonding in Metals
• The valence electrons of metal atoms can
be modeled as a sea of electrons.
• That is, the valence electrons are mobile
and can drift freely from one part of the
metal to another.
• Metallic Bonding Animation
Alloys
• Mixtures composed of two or more
elements, at least one of which is a metal.
• Their properties are often superior to those
of their component elements.
Learning Check
Give the ionic charge for each of the
following:
A. 12 p+ and 10 e1) 0
2) 2+
3) 2B. 50p+ and 46 e1) 2+
2) 4+
3) 4-
C. 15 p+ and 18e2) 3+
2) 3-
3) 5-
Learning Check
A. Number of valence electrons in aluminum
1) 1 e2) 2 e3) 3 eB.
Change in electrons for octet
1) lose 3e2) gain 3 e3) gain 5
eC.
Ionic charge of aluminum
1) 32) 5-
3) 3+
Solution
A. Number of valence electrons in aluminum
3)
3 eB.
Change in electrons for octet
1)
lose 3e-
C.
Ionic charge of aluminum
3) 3+
Review..
• What is a chemical bond?
– Force that holds two atoms together
• What is an ionic bond?
– An electrostatic force that holds
oppositely charged particles together
in an ionic compound
– Forms when….?
• What are atoms and compounds always
trying to achieve?
– Stability
– Complete set of valence electrons…