Dissolving is about ATTRACTION! Part I: “Like dissolves Like” Dissolving is about ATTRACTION!

OUTCOME QUESTION(S): C11-4-03 DISSOVING PROCESS Vocabulary & Concepts Describe and give examples of various types of solutions. Include: suspension, emulsion, colloid, alloy, solute, solvent, soluble, insoluble, miscible, immiscible Describe the chemical structure of compounds in terms of electronegativity and polarity of bonds. Include: polar and non-polar Explain the solution process of simple ionic and covalent compounds, using visual, particulate representation and chemical equations Include: hydration, heat of solution, dissolve, dissociate Vocabulary & Concepts  Dipoles Solvation

Electronegativity Scale (0-4) that represents the attraction an atom has for the shared pair of electrons in a bond Most electronegative element is fluorine (F) = 4.0 Least electronegative element is cesium (Cs) = 0.7 In a compound, the atom with the higher electronegativity pulls the SHARED electrons closer

The interaction of the electrons between atoms determines the three types of possible bonds

Ionic bonds are easy to identify – look for metal? Give/take of electron(s) to one atom in the bond Caused by very large difference in EN values Results in positive and negative IONS Ionic bonds are easy to identify – look for metal? - + EN = 0.9 EN = 3.0

Most covalent bonds are polar 2. POLAR Covalent Bond Unequal sharing of electrons towards one atom bigger the difference in EN, more polar the bond Creates permanent +/- regions: DIPOLES Most covalent bonds are polar HCl δ+ δ- Electrons pulled towards one side create a negative “end” and positive “end” + + EN = 2.1 EN = 3.0

Diatomics and compounds of just C and H are common non-polar examples 3. NON-POLAR Covalent Bond Equal sharing of electrons between atoms very small or NO difference in EN NO permanent dipoles Diatomics and compounds of just C and H are common non-polar examples C H propane C H Cl chlorine gas EN = 2.5 EN = 2.1 methane EN = 3.0 EN = 3.0

Note: Some molecules can contain polar bonds, but because of the shape are considered to be non-polar molecules. The geometry of some molecules cause all the polar “pulling” to cancel out resulting in no dipoles overall

**The general dissolving rule is like dissolves like** Solvation: the process of dissolving… Particles of solute will dissolve IF there is more attraction to the solvent particles than to itself.

Dissolving is usually endothermic overall There are 3 steps to the dissolving process: 1. Solute particles must break apart. Requires energy (called Lattice energy) 2. Solvent particles spread apart to make room. Requires energy 3. Solute and solvent particles attract together. Releases energy Dissolving is usually endothermic overall Heat of solution: The sum of the energy changes for dissolving.

Water is a POLAR molecule Hydration: dissolving with water as the solvent If the solute is attracted to water it will dissolve H2O δ- δ+ + + EN = 3.5 EN = 2.1 + δ+ EN = 2.1

- - √ Case 1: Polar solvent (water) with Ionic solute + + DISSOLVE δ- δ+ DISSOLVE H O δ- δ+ H O δ- δ+ √ H O δ- δ+ - Cl Cl - Na + + Na 3 steps to dissolving: 1. Solute particles break apart. 2. Solvent particles spread apart. 3. Solute and solvent particles attract. Dipoles attract Ions… Attractive Force

Dipoles attract Dipoles… Case 2: Polar solvent (water) with Polar solute H O δ- δ+ DISSOLVE H O δ- δ+ H O δ- δ+ √ H O δ- δ+ H O C δ- δ+ H O C δ- δ+ Dipoles attract Dipoles… Attractive Force

X Case 3: Polar solvent with Non-polar solute DISSOLVE δ- δ+ DISSOLVE H O δ- δ+ H O δ- δ+ X H O δ- δ+ C H C H C H Attractive Force Nothing to attract…

No attraction or repulsion – free to mix Case 4: Non-polar solvent with Non-polar solute DISSOLVE √ H C H C H C C H C H C H No attraction or repulsion – free to mix Attractive Force

The more soluble a solute, the more attracted **The general dissolving rule is like dissolves like** Solutes are attracted to charged solvents to various degrees: Remember that solubility is a relative term The more soluble a solute, the more attracted to the solvent it must be Solute Solvent Polar Non-polar Ionic √ X

Allows tiny spheres of grease to "dissolve" in water SOAP Has a polar end and a non-polar tail. Non-polar tail attracts oil Polar head attracts water H O H O H O Allows tiny spheres of grease to "dissolve" in water H O

CAN YOU / HAVE YOU? C11-4-03 DISSOVING PROCESS Vocabulary & Concepts Describe and give examples of various types of solutions. Include: suspension, emulsion, colloid, alloy, solute, solvent, soluble, insoluble, miscible, immiscible Describe the chemical structure of compounds in terms of electronegativity and polarity of bonds. Include: polar and non-polar Explain the solution process of simple ionic and covalent compounds, using visual, particulate representation and chemical equations Include: hydration, heat of solution, dissolve, dissociate Vocabulary & Concepts  Dipoles Solvation