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    okay, studying for a chemistry exam, and having some trouble with some questions.

    1. What is meant by the term "shielding"? What does shielding help to explain?

    2. What might have similar chemical and physical properties of lithium and why?

    3. Describe a crystal lattice?

    4. Distinguish between the conductivity of ionic and covalent compounds dissolved in water. Distinguish between the malleability of ionic compounds and metals.

    5. What role does hydrogen bonding play in boiling points?

    6. What is the most important difference between covalent, ionic and metallic bonding?

    They're kind of scattered through out the different subjects, but if you can answer or help me with any of them, that would be great.
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    1. It's basically where the electrons which are closer to the nucleus so the outermost electron isn't held on very tightly. This explains why the bigger metal species are more reactive than the smaller ones, and why the smaller non-metals are more reactive than the bigger ones.

    2. Other elements in the alkali metal group/group 1. Same amount of outer electrons.

    3. Oppositely charged ions held together by electrostatic forces. http://en.wikipedia.org/wiki/NaCl

    4. I don't know about the conductivity. Ionic compounds are very brittle and shatter easy because if the ions shift so that there are two Na+ or two Cl- next to each other, they will repel. Metallic compounds don't have this problem because the delocalised electrons allow the equally sized positive metal ions to slide over each other, so they are much less brittle. Adding a different type of metal (making an alloy) makes the metal stronger because of the different sized bubbles.

    5. The 3 type of intermolecular bonds are (in order of strength) van der Waals, permanent dipole-dipole and hydrogen bonds. van der Waals are found in non-polar compounds such as I2. Permant dipole-dipole are found in polar compounds such as HCl and Hydrogen bonds are found in compounds that contain bonds between H and N, O or F.
    Permanent diploe-dipole and hydrogen bonds are caused by differences in the electronegativity of the two species involved in the bonding. H bonds effect boiling point because they are the strongest and are around 1/10 the strength of a covalent bond. This is why water is a liquid, not a gas.

    6.Covalent - Electrons are shared from both species
    Dative/coordinate covalent bonds - All electrons involved in bonding come from one species (eg Ammonium)
    Ionic - Electrons are donated/accepted forming ions
    Metallic - Positive metal ions are surrounded by a sea of delocalised electrons
 
 
 
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