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

One or more electrons

Two same or different atoms

Atoms of the Same Strength (Covalent)

• There is no winner.• The two atoms share the electrons equally

with each other.

One or more electrons

Two atoms of similar strength

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

One or more electrons

Two somewhat different strengths

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

One or more electrons

Low electronegativity

• The attraction between the two oppositely charged ions is called an Ionic Bond

High electronegativity

Indicating the bond typeType 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