2. The atom has a centrally located nucleus with a positive charge. + surrounded by a cloud of electrons (with a negative charge).

3. Ionic substances (electrolytes) bond by a process of transferring electrons to become stable. Na Cl Na An electron is transferred from sodium (Na) to chlorine.. forming two oppositely charged ions.. which attract each other forming an ionic bond. Na Chloride is surrounded by sodium ions, Na sodium in turn is surrounded by chloride. which is surrounded by sodium and so on. Cl

4. Molecular substances bond by sharing electrons to become stable. H Cl Covalent bond Covalently bonded substances form molecules. Ionic bonded substances do not form molecules.

5. This type of interaction, covalent bonding, would be considered to be intramolecular (within the molecule). What we’ll be seeing is the interaction between molecules, intermolecular, ‘bonding’ between molecules.

6. Here’s an example of two elements forming a covalent bond. Hydrogen comes in pairs. It is already covalently bonded. So is oxygen. H2H2 O2O2 H2H2 Covalently bonded substances form independent molecules. water

7. Ionically bonded substances form crystal lattices. NaCl

8. When atoms covalently bond, the electrons might not be shared equally between the two atoms. Cl H 2.1 3.5 Chlorine has a greater electronegativity….. a stronger attraction for the shared electrons. Electrons are pulled towards the chlorine side..... and away from the hydrogen nucleus. Causing this side to have a slightly negative charge...  and this side to have a slightly positive charge. 

9. HCl This is a polar molecule. A molecule that has a dipole (2 poles).   Vectors are used to indicate the direction of electron pull.

10. HCl   Molecules that are polar attract each other. HCl      

11. Of course, two atoms that share their electrons equally would be nonpolar. Cl 3.5 Cl Equal sharing of electrons = nonpolar bond

12. Which would boil or vaporize first? Polar molecules Nonpolar molecules Nonpolar substances are usually gases or have low boiling points.

13. Hydrogen bonding is an extreme case of polar bonding. HF HN- HO- Hydrogen with just one electron to share Three of the highest electronegative elements.

14. H O H 3.5 2.1 Water is an example of hydrogen bonding between molecules of water. Between both H-O bonds, oxygen has the greater pull on the shared electrons. The result is that the electrons in both H-O bonds are pulled towards the oxygen atom.   

15. H O H Water is an example of hydrogen bonding between molecules of water.   

16.       This is hydrogen bonding. Hydrogen bonding is the attraction between molecules when hydrogen is bonded to oxygen, fluorine or nitrogen.   

17.       NH3NH3 H2OH2O HFHF H bonding between three different molecules. HFHF NH3NH3 H2OH2O   

18. H F   H F   H F   H F   Hydrogen bonding – when H is bonded to F, O, or N it is attracted to F, O, or N on a neighboring molecule.

19. H O H    H O H H O H H O H

20. C O H H H H CH 3 OH C O H H H H C O H H H H

21.       NH3NH3 H2OH2O HFHF H bonding between three different molecules. HFHF NH3NH3 H2OH2O   

22. H F H O H H N H H H bonding between three different molecules.

23. Even nonpolar molecules have some weak attraction between molecules. Consider the equal sharing of electrons in a Cl 2 molecule. Cl Cl 2

24.     As the molecules near each other the electron clouds are repelled from each other. Causing the molecules to temporarily become polar. This type of attraction between nonpolar molecules is called London dispersion forces. Cl 2

25.     HCl Review dipole-dipole forces HCl hydrogen bonding       H2OH2O H2OH2O London dispersion forces     The charged side on a molecule is attracted to the oppositely charged side on another molecule. The hydrogen proton on one molecule is attracted to the negative side of another molecule when H is bonded to F, O, or N. Temporary dipoles are induced when two molecules near each other. When heat is removed, the molecules lose their energy of motion, slow down and the intermolecular forces will hold the molecules solidly in place. In this case forming ice. Removing even more heat is needed to solidify this substance.

26. It’s these intermolecular forces that cause molecules to become solids. It explains why substances freeze and boil at different temperatures. For example, it’s the hydrogen bonding between water molecules that cause water to change to ice. It explains why substances are solids, liquids and gases at room temperature.

27. Ionic substances strong ionic bonding between charged ions Polar covalent weak attraction between slightly charged molecules solid (crystals) liquid, gas or solid Nonpolar covalent weaker attraction between non-charged molecules gas or liquid

28. Types of Intermolecular Forces Ion-Ion forces (ionic bonding) NaCl, NH 4 NO 3 Ion-dipole forces NaCl in H 2 O Hydrogen bonding H 2 O, NH 3, HF Dipole-dipole H 2 S, HCl, CH 3 Cl London forces Ar, O 2, N 2 Types Examples

29. Sample Exercise 11.3 List the substances BaCl 2, H 2, CO, HF and Ne in order of increasing boiling points. BaCl 2 London forces ion-ion H2H2 CO dipole-dipole HF hydrogen bonding Ne London forces H 2 < Ne < CO < HF < BaCl 2 First, identify the type of intermolecular force, then arrange them from weakest to strongest.