For the following intermolecular forces:

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1 Lecturenotes 1 unit6_review_exercise_2017.odt

2 Lecturenotes 2 unit6_review_exercise_2017.odt

3 Lecturenotes 3 unit6_review_exercise_2017.odt

4 Lecturenotes 4 unit6_review_exercise_2017.odt

5 Answers: 1. Ionic bonds occur when a less electronegative atom, usually a metal loses one or more valence electrons to a much more electronegative atom. The result from the loss/gain of electrons is an ionic bond which is the attractive force between the negatively and positively charged ions. This is the force that holds together the particles in an ionic compound. 2. When 2 atoms share their valence electrons to attain a stable octet of electrons, the attractive force between an atom and the other atom's electrons is called a covalent bond. Covalent bonds occur between non metallic atoms. When all of the atoms in a substance are covalently bonded together, rather than forming individual molecules, the substance is known as a network solid. Network solids are very hard and have very high boiling points because to break them or vaporize them requires breaking the covalent bonds. 3. Dispersion forces occur when the electrons in the outer electron clouds shift to one end of the molecule, resulting in a temporary dipole. These temporary dipoles are weakly attracted to each other and the force is known as dispersion force. This force is present in all molecules, but is much weaker than dipole forces or hydrogen bonding. Because it is so weak, it is only important in molecules that are not dipoles. 4. Hydrogen bonding occurs in dipole molecules that have hydrogen bonded directly to N, O, F or Cl. These very electronegative atoms attract the electrons around the hydrogen so strongly that the hydrogen atom becomes temporarily positively charged and can then form a bond by sharing the electron pair from one of the electronegative atoms on a neighboring molecule. This results in a bond that is considerably stronger than an ordinary dipole, but is weaker than a full covalent bond. 5. Dipole interactions are the forces between dipoles that are the attraction between the positively charged end of one dipole with the negatively charged end of another dipole. These forces are found in any molecules that form dipoles. The weakest IM forces are dispersion forces followed by dipole interactions, hydrogen bonds, ionic bonds and covalent bonds. However, dispersion forces can become quite strong in large molecules and can be stronger than the other Van Der Waals An example of this is the fact that iodine, I 2 is a solid at room temperature while water, with strong hydrogen bonding is a liquid. An Iodine molecule with its 106 electrons is much larger than a water molecule which has only 10 electrons. Covalent bonds in network solids are the strongest forces as is shown by the extremely high melting points in network solids. Lecturenotes 5 unit6_review_exercise_2017.odt

6 6. a. CH 4 < CO 2 CO 2 and CH 4 both have low boiling points due to the dispersion forces, which are the weakest of all IM forces, but CH 4 has weaker dispersion forces because it has fewer electrons. b. HCl < H 2 O Both HCl and H 2 O have hydrogen bonding, but the H - O bonds in water are much more polar than the H-Cl bonds in HCl. In addition, water molecules can form 4 hydrogen bonds per molecule while HCl can only form 2 hydrogen bonds to each molecule. Both of these factors lead to weaker hydrogen bonding in HCl compared to H 2 O c. CH 4 < NH 3 These molecules are approximately the same size so their dispersion forces are approximately equal, but NH 3 is a dipole molecule and hydrogen bonds which gives it a much higher boiling point compared to CH 4 d. NaCl < Graphite NaCl is held together by ionic bonding which is stronger than any of the Van der Waals forces and graphite is a network solid held together by covalent bonds which are stronger than any of the other intermolecular The boiling point of a substance is affected by the strength of the intermolecular attractions, with stronger attractions leading to higher boiling points. 7. Metals conduct electricity as solids because their metallic bonds consist of + ions surrounded by the free moving valence electrons that attract the ions. Because the force from the electrons is not completely dependent on the position of the metal atoms, metallic substances can bend without breaking. Ionic solids consist of + and - ions that are held together by attraction to each other. Since the like charged atoms repel each other, they must be in a specific position to be bonded together. This keeps them from conducting since the charges can't move and also makes ionic substances brittle because any movement of individual ions causes the whole structure to fall apart from the repulsion of like charged ions. Lecturenotes 6 unit6_review_exercise_2017.odt