Solutions to Solutions: Wrap-up
1) A model of an atom:
2) The majority of the mass of an atom is contained in its nucleus.
3) Protons and neutrons are relatively “heavy” compared to electrons. The mass of an atom primarily comes from the number of protons and neutrons.
4) Relative Size of the Nucleus and the Atom: if an atom were the size of a
5) Shells: For a shell to be “complete” (stable) it needs to be ‘full’ of electrons. a. The first shell of each element can only contain 2 electrons – it’s a small shell and the electrons are close together. b. All other shells need 8 electrons to be complete ( there are exceptions to this ). c. The shells actually have “names”… like s, d, p, and f. More on that later! d. The electrons in the OUTERMOST shell have a special name:
“valence electrons”. These are the electrons that get shared or swapped in covalent or ionic bonding.
6) Covalent Bond: a type of ‘connection’ between atoms when they SHARE a pair of electrons. Covalently bonded atoms form a MOLECULE.

a) Sugar is a compound made up of carbon, hydrogen and oxygen. It forms because of covalent bonding. It doesn't conduct electricity when dissolved because it is not composed of charged particles. b) Vinegar is also made up of carbon, hydrogen and oxygen. Most of the bonds are covalent but one of the hydrogen atoms is bonded to an oxygen and can "dissociate" and conduct electricity.
A covalent bond forming H
2
(right) where two hydrogen atoms share the two electrons.
7) Ionic Bond: bonding that is characterized by “swapping” of electrons.
One atom gives up an electron completely and the other takes the electrons. BUT, they don’t leave each other because each of them is now ‘charged’. The dude who gave up an electron is “+” and the dude who takes the electron is “-“. So, they are still attracted to each other. a) Ionically bonded atoms do NOT form a molecule… they create a
“formula unit”. b) NaCl. This is a unique partnership because Na has 1 valence electron and Cl has 7 valence electrons. Remember that valence shells (mostly) like to have 8 valence electrons? Well, Na ‘gives’ Cl it’s electron. So, now it has just the full inner shell. Cl ends up with all 8 valence electrons. Na ends up withOUT that extra valence electron so now it's "outermost shell" is also full. So, NaCl is really stable as a solid.
Question: does NaCl form a compound as an ionic OR as a covalent bond? Ionic.

8) Charge: A molecule like water can be neutral overall, yet exhibit charged regions on portions of the molecule.
Example: A coffee stand sells coffee and really yucky muffins. Let's say they make $100 on coffee ("+"), but they lose $100 on pastries
("-"). Part of the business is "positive" and part is "negative" but overall, they come out even (or ZERO). a) Remember, that NEUTRAL is not a 'charge'. It is the balance between positive and negative charges on an atom. (between protons and electrons). b) An ion is an atom (or group of atoms) that is NOT electrically balanced overall. It can have a net positive or net negative charge. For instance, a sodium ion has a net charge of "+1" when it loses 1 electron. We would write this as Na 1+ .
9) Polar covalent bond: this is a special type of covalent bond in which they don't "share" the electron equally. The bonded atoms have an
"unequal" attraction for the shared electrons, and there is an unequal distribution of charge.
10) Non-polar covalent bond: the bonded atoms equally share the electrons. This results in a balanced distribution of the charges.
11) Electronegativity: a measure of an atom's ability to attract electrons.
12) Polarity: it is possible for an electrically neutral object (like a water molecule) to 'act' as if it is charged... like a magnet. One end is slightly positive, the other end slightly negative. Polar molecules 'have a dipole '.

13) Dipole: equal but opposite charges that are separated by a small distance. Water molecules have permanent dipoles. Wax molecules have essentially NO dipoles, and are therefore non-polar!
14)
In general, when molecules have strong dipoles - like sugar - they separate more easily and it can result in increased solubility in water.
15) Solubility: depends on several factors. a) water is a polar covalent molecule. It is most effective at dissolving other polar covalent molecules or ionic formulas. b) Solubility changes with temperature and also with pressure (for gases). Think about mixing a powdered drink-mix into water. Some of the sugar is likely to sit at the bottom unless you heat up the water... then... voila.
15) Additional Notes: a) Conductivity: substances will conduct electricity if they have particles with a net charge that are mobile. Pure water doesn't conduct electricity

because - even though it is polar - the charges within the water molecule are
NOT free to move around. b) Many of the electrical insulators are found on the "right side" of the periodic table, such as carbon, oxygen, nitrogen, and sulfur. Plastics, synthetics and glass are examples. b) Some substances readily 'give up' electrons (like glass) and other substances readily 'take' electrons, like plastic. So, when we rubbed the plastic knife on our clothes, it became negatively charged (and our clothes became positively charged). The opposite occurs when you rub a test tube on your clothes! c) There is a difference between:
The effects of electrical interactions between molecules versus
The electrical interactions within molecules. d) Metallic Bonding is something “in between” covalent and ionic bonding.
It is called an “electron sea”.
"It worked." (said after witnessing the first atomic detonation).
J. Robert Oppenheimer
I am become death, the destroyer of worlds.
J. Robert Oppenheimer