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Chemistry Lesson 1
Atomic and Molecular Structure

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Instruction 1-2

Connection Among the Location in the Table, the Atomic Number, and Mass | How to Identify Metals, Semimetals, Nonmetals, and Halogens | How to Identify Alkali Metals, Alkaline Earth Metals, and Transition Metals | Lanthanide, Actinide, Transactinide, and Transuranium Elements | Ionization Energy, Electronegativity, Relative Sizes | How Many Electrons Can Bond? | Size and Mass | Location and Quantum Electron Configuration | Summary


As we learned in our last Instruction, scientists know of at least 118 elements – and there are probably more to come. Most of these elements are metals. http://www.chem.lsu.edu/lucid/tutorials/Periodic_Table.html 

Where do you find metals on the Periodic Table of the Elements? They are on the left and center, since there are so many of them. But we thought a little Element Spotting Guide wouldn’t hurt. You should probably look at the Periodic Table of the Elements while you read this Instruction. Notice that hydrogen is considered a nonmetal, as well as all of Group 18, most of Groups 17 and 16, and some from Groups 15 and 14. The metalloids (sometimes called semimetals) are 7 elements that occupy a stair-like trend in the large block on the right. All the rest are metals.


Some metals are bright and shiny like platinum (Pt) or silver (Ag) or gold (Au). There are other metals you have probably never heard of, like iridium (Ir) and rhenium (Re). But all metals have similar physical and chemical properties.

First of all, metals are good at conducting electricity and heat. Which is why gold (Au) and copper (Cu) are used in electronics.

Metals usually have one, two or three electrons in their outer shells (remember shells, or “energy levels,” from our last Instruction?) This means that they tend to lose electrons as they search for other elements to bond with. When metal atoms are together in a group, there is usually a swarm of semi-loose electrons whirling around them. This swarm is called an “electron gas” and it reflects light. It is this reflected light that makes metals look shiny.

Metals are very cohesive and reactive. “Cohesive” means that they cling tenaciously to other metal atoms. “Reactive” means that they combine easily with other elements to form compounds. Sodium (Na) and potassium (K) are two of the most reactive elements. Sodium chloride (NaCl) is a good example of what happens when a metal (Na) reacts with another element, chlorine (Cl). And who’d want to eat French fries without it? (Sodium chloride is table salt).

Metals are also malleable, which means they can be hammered into thin sheets. And they are ductile, which means they can be drawn out into a long thin wire. These properties give them many practical uses.

Incidentally, in case you’re wondering why the elements have the symbols they do, it’s not just arbitrary and weird. It’s because many of the symbols come from the ancient names for the elements. For example, gold used to be called aurum, which is why its chemical symbol is Au and iron used to be called, so its symbol is Fe.   


The properties of nonmetals are very much the opposite of metals. Metals are shiny, nonmetals are dull. Metals are hard, nonmetals are soft or powdery. Metals are ductile and can be shaped, nonmetals fracture easily. Most metals have higher melting points than most nonmetals.


You can probably guess that since the metalloids occupy the area between the metals and the nonmetals, their properties are somewhere between metals and nonmetals. The elements that are considered metalloids are: boron (B), silicon (Si), germanium (Ge), arsenic (As), antinomy (Sb), tellurium (Te), and astatine (At).

Halogens and Noble Gases


Halogens are the nonmetals that are in Group 17 of the Periodic Table of the Elements; they are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (As). The halogens have 7 electrons in their outer shell. Halogens often bond with metals. They are very reactive, but as you move down the column, their reactivity decreases. They are poisonous. Fluorine and chlorine are yellow-green gases, bromine is a red-brown liquid and iodine is a blue-black solid (which turns purple when it becomes a gas).

The noble gases are the elements in Group 18; they are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). They were given the name noble gases since they are very unreactive (much like the noble metal gold). The reason why these elements rarely react is because they already have a full outer shell. But that doesn’t mean they aren’t useful. Neon (Ne) is one of these gasses – and Times Square wouldn’t be Times Square without the neon used in its big bright advertising signs.

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for Students, Parents and Teachers

Now let's do Practice Exercise 1-2 (top). 


Next Page:  How to Identify Alkali Metals, Alkaline Earth Metals, and Transition Metals (top)