9/21/09

Post date: Sep 21, 2009 3:3:42 PM

Bell Activity: Why do people form connections with other people?

    • Why chemical bonds form

      • Each atom wants to have a stable number of electrons

    • More atom anatomy

      • Charges

        • Atoms are made of protons, neutrons, and electrons

        • Protons have positive charge, electrons have a negative charge, neutrons have no charge

        • When not bonded, atoms have the same number of protons and electrons, so net charge is 0

      • Electrons

        • Arranged in different levels or orbitals, with each level being able to hold a certain number of electrons

        • Valance electrons - the electrons in the outer-most level, involved in chemical bonding

          • Periodic table shows us how many valence electrons different atoms have by which column the element is in

        • Atoms want to have their outermost electron level filled up completely, and can do this in 2 ways

          • Take more electrons from another atom or give up electrons to another atom

            • When an atom gains electrons or gives them up, it is called an ion

          • Share electrons with another atom

          • These two methods result in 2 different types of bonds

        • Ionic bonds

          • Formed when one atom gives electrons to another

          • One atom is looking to get rid of electrons, another wants to get more, so electrons are transferred

          • The atom that gave up electrons has lost negative charge, and now has a positive charge. The atom that got more electrons has gained negative charge, and now has a negative charge. Since opposite charges attract, the positive ion is attracted to the negative ion.

          • Example: sodium bonding with chlorine

            • Sodium has 11 total electrons (atomic number is 11) and 1 of those is a valence electron (sodium is in the first column of the periodic table)

            • Chlorine has 17 total electrons (atomic number is 17) and 7 of those are valence electrons (7th column)

            • Sodium wants to get rid of one electron (so it has 8 valence electrons) and Chlorine wants to get one more electron (so it has 8 valence electrons)

            • Sodium gives one electron to Chlorine

            • Sodium (who lost one negative charge) now has a charge of +1 while Chlorine (who gained one negative charge) now has a charge of -1. The opposite charge attract each other, and the Sodium and Chlorine are pulled together.

      • Ionic analogy (due today in class)

          • In groups of 2 or 3, create an analogy for ionic bonds.

          • Write at least one paragraph explaining the analogy.

          • Present to the class tomorrow (Tuesday)

          • Example: My dog has 4 puppies, but I can only keep 2 of them. I give the other two to you, because you don't have any puppies and want 2. I then make it a point to keep in contact with you so that I can visit the other puppies, and we are thus "bonded" together.

        • Sometimes atoms don't bond in equal numbers

          • Example: Magnesium bonding with Fluorine

            • Magnesium is in the 2nd column, so it wants to get rid of 2 electrons

            • Fluorine is in the 7th column, so it wants to add 1 electron

            • One atom of Magnesium needs to bond with 2 Fluorines to get rid of both of its extra electrons

            • Formula: MgF2

      • Ionic Bonding Homework (due tomorrow)

        • For each of the following combinations: draw each atom, show how the electrons move using arrows, and write the formula for the compound.

        1. Beryllium and Oxygen

        2. Potassium and Nitrogen

        3. Magnesium and Chlorine

        4. Calcium and Sulfur

        5. Magnesium and Nitrogen