Transcript 2_ch-6-ionic

Chapter 6
Ions
• Elements within each group of the periodic
table behave similarly because they have
the same number of valence electrons.
• Valence electrons are the electrons in the
highest occupied energy level of an
elements atoms.
– Valence electrons determine the chemical
properties of an element.
Valence Electrons
• To find the number
of valence
electrons in an
atom of a
representative
element, simply
look at its group
number.
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 Gain 4 electrons
N would like to Gain 3 electrons
O would like to Gain 2 electrons
Key Concept
• Atoms of metals
lose their valence
electrons.
• Atoms of some
nonmetals ten to
gain electrons or to
share with other
nonmetallic
elements to achieve
a complete octet
Formation of Cations
• When an atom loses an electron it
produces a positively charged ion, or a
cation.
• The most common cations are those
produced by the loss of valence electrons
from metal atoms.
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.
Ionic Bonds: One Big Greedy Thief Dog!
Formula Units
• A chemical formula shows the kinds and
numbers of atoms in the smallest
representative unit of a substance.
• Because an ionic compound exists as a
collection of positively and negatively
charged ions arranged in repeating
patterns, its chemical formula refers to a
ratio known as a formula unit.
• 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 electron dot
structures to
determine formulas of
the ionic compounds
formed when
• 1. potassium reacts
with iodine.
• 2. Aluminum reacts
with oxygen.
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.
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
Metallic Bonds: Mellow dogs with plenty
of bones to go around.
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…