comparing ionic and covalent bonding.notebook October 16, 2014 Bond strength IMF strength Oct 6 10:43 AM Oct 14 10:06 PM

Transcription

1 Bond strength IMF strength Oct 6 10:43 AM Oct 14 10:06 PM 1

2 Oct 14 10:07 PM Oct 14 10:07 PM 2

3 Oct 14 10:10 PM Oct 14 10:11 PM 3

4 comparing ionic and covalent bonding.notebook October 16, 2014 Hardness Ionic compounds are harder than covalent compounds due to the strength of ionic bonds. Oct 14 10:14 PM 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. Oct 14 10:18 PM 4

5 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. Non polar 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 15 8:11 AM ALL students who did not write the inclass 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 16 8:15 AM 5

6 Structure and Properties of Ionic/Molecular Substances Practice Problems 1. Classify the following substances as ionic, polar covalent, or nonpolar covalent. MgF 2, CH 3OH, CF 4. Describe how you could perform tests to distinguish between these compounds. MgF 2 ionic, CH 3OH polar covalent, CF 4 nonpolar covalent Ex: Try to dissolve each in water. Insoluble compound would be CF 4. The other two would dissolve in water; test each solution for conductivity, MgF 2 should conduct electricity, CH 3OH 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, three dimensional 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 non polar 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 non polar 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, CHCl 3, has the same shape as a molecule of methane, CH 4. 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. Oct 14 10:21 PM Oct 14 10:44 PM 6