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 type Type of BondNonpolar CovalentPolar CovalentIonic Electronegativity difference < > 2.1 DiagramH--|--HH---|-ClNa----|Cl ElectronsShared EquallyShared UnequallyTransferred

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 – Reflect and Connect #1-4 – Due next class period