Lessons 18 and 19

Lesson 18:

This lesson gave us a closer look at the patterns that occur in the periodic table. We notice repetition in the number of electron shells in an atom of an element as well as how many valence electrons n element has. Substances in the same group usually have the same number of valence electrons, while elements in the same periods (the horizontal rows) usually have the same number of electron shells. We call the apparatus in which electrons float a shell when we diagram an atom, but when we actually look at an atom, they collect in "clouds" around the nucleus--a topic for a different time. As you move up and down the periods (NOT right to left), the number of shells increases or decreases. As you move right to left through the groups, (1A, 2A, 3A, etc.) you see the number of valence electrons begin to increase until you reach the noble gases.

Problems:
3.) What do Be, Mg, and Ca all have in common? All three elements are found in Group 2A of the periodic table. They have two valence electrons and would probably bond best with 6-valence halogens like O, S, and Se.

8.) For element 50, answer:
a.) Name, symbol, group #: Tin, Sn, Group 4A
b.) Number of protons: 50
c.) Number of neutrons: 50 (roughly, in a neutral atom)
d.) Number of electrons in a neutral atom: 50
e.) Number of valence electrons in a neutral atom: 4
f.)  Number of core electrons in a neutral atom: 46
g.) Three other elements w/ same # of valence electrons: Ge (Germanium), Si (Silicon), and C (Carbon).

Lesson 19:

In this lesson, which talked about chemical stability of elements, we learned that some atoms bond more readily than others. For example, the noble gases do not easily bond with other elements because they have a full set of valence electrons (usually 8), whereas the elements in Group 1A of the periodic table need 7 electrons and will bond with just about any halogen to gain a stuffed outer shell. We can pinpoint a section of the table where it's easier for atoms to gain their electrons rather than give them up. For example, it's easier for an oxygen atom, which has 6 valence electrons, to gain 2 rather than deal out those 6, whereas an atom of lithium, with just 1 valence electron, would be better off relinquishing it. Elements usually bond in set ratios to achieve an overall neutral charge, with one atom being positive, a cation, and the other being negative, an anion.

(Here's a nifty tip: if you have trouble remembering the difference between cations and anions, think: anion = "a negative ion". The 't' in cation looks like a plus sign, so cations are positively charged!)

Problems:
2.) Explain what is meant by "noble gas envy". Elements that sit more to the left of the periodic table have a lower number of valence electrons and yearn for a full outer shell, which is why they bond so quickly with other atoms. Every element wants to look like a noble gas, with those perfect 8 electrons.

11.) What is the symbol of an ion with 22 protons, 24 neutrons, and 18 electrons? Ti, Titanium, has 22 protons and, in this scenario, would be positively charged.

12.) When chlorine gains an electron to become a chloride ion with a -1 charge, it ends up with the electron arrangement of argon. Why doesn't it become an argon atom? The chlorine atom originally had 7 valence electrons, and by gaining one, it succeeded in resembling a noble gas--argon. However, its identity did not change, because the only way chlorine could become argon would be if the number of protons increased by 1.