Transcript Ionization versus Dissociation

Ionization versus Dissociation
Ionization
• To remove a negative charge from a positive
charge.
• The process of separating electrons from
protons is called ionization.
Dissociation
• Some very similar to ionization that happens
to solids. When the ions in a crystal lattice are
separated, the process is called dissociation.
Example: sodium chloride in water.
• Dissociation occurs because of solvation,
which requires interaction of similarly
electrical properties.
Differences between Ionization and
dissociation
• Ionization, the force comes from within the
atom.
• Dissociation, the force comes from outside the
atom and is the interaction between two or
more compounds.
Ionic Compounds
• Ionization takes place to form solid ionic
crystals.
Example: Sodium Chloride (Table salt)
– Positive sodium ions and negative chloride ions
• Ionic crystals can then interact with water
molecules to dissociate.
– Resulting in a solution that conducts electricity.
Microscopic Representation of
Ionization
• Energy must be added to the neutral atom to
remove an electron from a proton.
• The amount of energy depends on the type of
atom.
Ionization is unique to the type of
atom
• Each element has a characteristic ionization
energy.
Example: Chlorine is 2.5 times greater than that
for sodium.
Importance in Understanding
Ionization and Dissociation
• Together these factors help explain important
macroscopic properties.
– Solubility
– Hardness
– Conductivity
Electronegativity
– Covalent Bonds: Bonding between atoms of
similar electrical properties.
– Ionization is one way to quantify the electrical
properties.
– Electronegativity is another way.
Electronegativity
• When two atoms of the same element bond
they form covalent molecules.
– Covalent because they share electrons
• When two atoms of different element form
covalent bonds, the sharing might not be
equal.
Why don’t some atoms share equally?
• Atomic Structure
– Some atoms are better at attracting electrons
than others.
• The ability to attract electrons is known as
electronegativity.
Linus Pauling
• An American chemist created a scale for
electronegativity.
– He assigned Florine an arbitrary value of 4.
• Florine is the most electronegative atom because it is
able to attract electrons better than any other element.
– Electronegativity values for other elements where
created based on a comparison to florine
Electronegativity
• Can indicate the type of bond that will form.
• HOW?
– Think Tug-of-War
Two same or different atoms
One or more electrons
Atoms of the Same Strength (Covalent)
• There is no winner.
• The two atoms share the electrons equally
with each other.
Two atoms of similar strength
One or more electrons
Atoms of Somewhat Different
Strengths (Polar Covalent)
• One atoms pulls the rope more than the other,
neither wins.
• More rope is to one side of the line
Two somewhat different
strengths
One or more electrons
A Polar Covalent Bond
• Results in a molecule that has regions of
positive charge and regions of negative
charge.
Atoms that have drastically different
values
• The atom with greater electronegativity will
win.
• Electron transfers from atom with low
electronegativity to an atom with high
electronegativity.
– Ions are formed.
Atoms that have drastically different
values
• The attraction between the two oppositely
charged ions is called an Ionic Bond
High electronegativity
Low electronegativity
One or more electrons
Indicating the bond type
Type of Bond
Nonpolar Covalent
Polar Covalent
Ionic
Electronegativity
difference
< 0.4
.4-2.1
> 2.1
Diagram
H--|--H
H---|-Cl
Na----|Cl
Electrons
Shared Equally
Shared Unequally
Transferred
Molecule vs Compound
• Both terms mean the same concept.
– Molecule is the smallest unit of a covalently
bonded compound.
• Molecules are covalently bonded atoms
– Ionic Compounds
• Formed by ionic bonding
Assignment
• Write in your Planner or Table of contents!
– I’ll be around to check before class is out.
• Page 135-139
– Reflect and Connect #1-4
– Due next class period