Sunday, September 2, 2012

Lessons 6, 9, and 10

The Basics of the Periodic Table:

These three lessons were mainly about the periodic table. We learned the factors that went into creating the table and why it's set up in the way that it is. We identified patterns within the groups/families in the table and determined where an element would be placed based off its properties. We briefly covered the importance of reactivity in organizing the table and went through the names of the groups (alkali, alkaline-earth, transition, halogen, and noble gas).

Lesson 6:

This lesson touched on both what an element is and how it can create compounds with other elements. Elements are represented by a capital and lowercase letter called a chemical symbol. In a compound, elements have to be combined in a specific ratio to produce the right substance afterwards. Sometimes you can end up with crazy colored substances after a reaction. Compounds can be in solid, liquid, or gas form.

Problems:
2.) What is meant by "physical form"? A physical form is a fancier way of saying 'solid', 'liquid', or 'gas'. It describes the state that matter is in at a given time or before/after a reaction.

3.) How many elements are included in the chemical formula for sodium nitrate, NaNO3? There are three elements here, in a given ratio. Na is sodium, N is nitrogen, and O is oxygen. There are 3 oxygen molecules, one nitrogen molecule, and one sodium molecule.

4.) What is the difference between NaOH(s) and NaOH(aq)? Both compounds are sodium hydroxide. The biggest difference is what lies in the parentheses--the (s) and the (aq). The s means that it's solid sodium hydroxide. The aq implies that the solid sodium hydroxide has been dissolved in water.

Lesson 9:

A man by the name of Dmitri Mendeleyev created the periodic table of elements. He organized elements by their reactivity and the number of valence electrons in their outer electron shells. Some elements within the table are placed right next to, or above and below each other because they react similarly with certain substances (i.e. water), and as you compare the reactions of different groups you can get starkly different results. Holes were left in Mendeleyev's "prototype" periodic table to make room for elements that existed but hadn't yet been discovered.

Problems:
2.) Which element would carbon (C) be more similar to: nitrogen (N), oxygen (O), or silicon (S)? Carbon is more similar to silicon (Si) than any of the other elements listed. If you look at the periodic table, Si lies just beneath C, and they are in the same group, which means that they have the same number of valence electrons in their outer shell and that they react in a similar way when combined with water. N and O are near C, but they are in different groups which means that they're subject to react differently than it.

4.) Look up the properties of iron, barium, or phosphorus and explain why nails are made of iron and not barium or phosphorus. 
Properties of iron: reacts with water to oxidate and form rust but does not explode. Is generally sturdy.
Properties of barium: Reacts with almost all nonmetals, forming poisonous substances, and reacts vigorously with water to release hydrogen gas.
Properties of phosphorus: Conducts electricity, almost never found in its pure form in nature, somewhat combustible (hence why we use it in matches)
If we made nails out of anything other than iron, we would probably have some serious infrastructure problems on our hands. That, or health hazards.

Lesson 10:

Elements are placed in the periodic table strategically. Violently reactive substances, like the alkali and alkaline-earth metals, find homes on the left side of the table, while elements that barely react at all (or that have to be forcefully combined by man) take up the right side. Elements that are somewhat reactive but relatively boring fill the center chunk of the table and make up the "transition metals". A zig-zag line toward the right side of the table splits the metals and nonmetals apart, and the elements that hug it we call metalloids.

Problems:
1.) Describe how reactivity changes as you go down Group 1A. Group 1A can also be called the alkali metal group, which means that all of its elements react violently with water. some even produce a flame. Hydrogen sits on top of the group and is usually emitted from chemical reactions involving the other elements in Group 1A. As you go farther down the period, the reactivity increases and your experiments become more dangerous. For example, compare the reaction between sodium (Na) and water to the reaction between cesium (Cs) and water. One produces a bigger spark and can sometimes cause the apparatus in which it's reacting to shatter.

5.) Which of the following elements are solid: fluorine (F), oxygen (O), titanium (Ti), potassium (K), lead (Pb), silicon (Si)? Titanium, potassium, lead, and silicon are all solids.

8.) Which elements can you make jewelry out of, and why? Copper (Cu), neon (Ne), sodium (Na), platinum (Pt). Well, good luck finding a way to make jewelry out of neon. It's a noble gas, which means it will not combine with any other element and it's a gas, which means it's not malleable. As for sodium, ever time you got your piece of jewelry wet, it would sizzle and fizz. Sodium is also soft enough to cut with a knife, so your jewelry would probably bend and/or break all the time. Copper is very malleable but also sturdy, being a solid. It doesn't react readily with water. Platinum is a transition metal (one of those boring elements) so it would also be good for jewelry.

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