comparing ionic and covalent bonding.notebook
October 16, 2014
Bond strength
IMF strength
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comparing ionic and covalent bonding.notebook
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comparing ionic and covalent bonding.notebook
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comparing ionic and covalent bonding.notebook
October 16, 2014
Hardness
Ionic compounds are harder than covalent compounds due to the strength of ionic bonds.
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Electrical Conductivity
Electricity is the flow of charge (movement of electrons). Covalents are
uncharged, so they cannot conduct electricity in any state. Solid ionics
cannot conduct electricity because their ions can not move, but in the liquid
state the ions are free to travel and therefore can conduct electricity.
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comparing ionic and covalent bonding.notebook
October 16, 2014
Solubility in Water
Water molecules are polar and have partial positive and negative poles.
Water molecules will dissolve (surround) particles they are attracted to, such
as other polar covalent molecules and ionic substances. Non­polar covalent
molecules will not dissolve, as the water molecules are more attracted to
each other and so will not surround (dissolve) the nonpolar substance.
Nonpolar = no solution!
Ionic / Polar = solution!
Oct 15­8:11 AM
• ALL students who did not write the in­
class assignment on intermolecular forces must do so today at lunch!!
• Quiz tomorrow: Intermolecular forces (VERY similar to assignment): can be picked up today at lunch, answer key will be online
Oct 16­8:15 AM
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comparing ionic and covalent bonding.notebook
October 16, 2014
Structure and Properties of Ionic/Molecular Substances
Practice Problems
1. Classify the following substances as ionic, polar covalent, or nonpolar covalent. MgF2, CH3OH, CF4. Describe how you could perform tests to distinguish between these compounds.
MgF2 ­ ionic, CH3OH – polar covalent, CF4 – nonpolar covalent
Ex: Try to dissolve each in water. Insoluble compound would be CF4. The other two would dissolve in water; test each solution for conductivity, MgF2 should conduct electricity, CH3OH would not.
1.
Explain why units of an ionic compound should not be called molecules.
Ionic compounds do not exist as individual molecules. They exist as regular, repeating, three­dimensional patterns called a crystal lattice made up of huge numbers of ions. Formula units for ionic compounds describe the ratio of ions in these crystals. 3. How does the sharing of electrons differ between a non­polar covalent bond and a polar covalent bond?
In a nonpolar covalent bond the atoms have equal electronegativities and therefore the electrons forming the bond are shared equally, that is they are located at equal distance between the atoms. In a polar covalent bond, one atom has higher electronegativity than the other and therefore pulls the electrons closer to itself.
4. Explain (using intermolecular forces) why an ionic compound can dissolve in water.
Water is a polar molecule. The partial negative pole on the oxygen of water is attracted to positive ions and will surround them, and the partial positive pole on the hydrogens in the water molecule are attracted to the negative ions of an ionic compound and will surround them, creating a solution.
5. Explain how the size (number of electrons) of a non­polar molecule affect the strength of London dispersion forces between the molecules. London dispersion forces are caused by temporary dipoles created by the motion of electrons. More electrons in a molecule would mean this motion would be more substantial creating more frequent and stronger poles.
6. A molecule of chloroform, CHCl3, has the same shape as a molecule of methane, CH4. However, methane’s boiling point is ­164ºC and chloroform’s boiling point is 62 ºC. Explain the difference between the two boiling points.
Methane is nonpolar which means that it has only weak LDFs holding the molecules together and therefore would boil at a very low temperature and exist as a gas under normal conditions. Chloroform is polar and its dipole/dipole forces hold the molecules together so it would take more energy to boil the liquid and pull the molecules apart to become a gas.
7. A chemist analyzes a white, solid compound and finds that it does not dissolve in water. When the compound is melted, it does not conduct electricity.
a) What would you predict about this compound’s melting point?
b) Are the atoms that make up this compound joined by covalent or ionic bonds?
1.
It would likely have a low melting point
2.
The atoms of this compound are joined by covalent bonds – which is why it does not conduct electricity. It is likely nonpolar which is why it did not dissolve in water.
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