Chemistry

Understanding the Periodic Table



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If you are not familiar with the periodic table of elements, when you first look at it, it may look like an undecipherable page of letters and numbers (actually, even if you are familiar with it, it may look like an undecipherable page of letters and numbers). However, do not be dismayed. Understanding the periodic table is actually easy.

It all started with a man by the name of Dmitri Mendeleev, a Russian chemist. While studying the chemical properties of elements, he noticed patterns (now trying to find patterns in elements may sound strange, but it was Dmitri's favorite past-time). In case I lost you when I mentioned elements, elements are simply substances that cannot be broken down into other substances by chemical techniques. To expand the definition a little further, elements are made up of atoms, and atoms are made up of different amounts of protons, neutrons and electrons. Protons, which are found in the nucleus, have a positive charge. Neutrons, also found in the nucleus, have no charge (they are the neutral guys, kind of like Switzerland). Electrons, found outside of the nucleus, have a negative charge.

Getting back to Dmitri, he found that he could arrange the 65 then-known elements into a table where each element had a higher atomic weight than the one on the left and was similar to the other elements in the column (now don't get excited by the words atomic weight; I'm about to explain this to you). The atomic weight of an atom is the mass of that atom compared to some standard. Early scientists came up with a system in which the weight of an element was determined by comparing it to the weight of another element (of course they could have chosen something like a car, but after all, they were scientists).

The current benchmark that scientists use to measure atomic weight is carbon-12. Therefore, an atomic mass unit, which is used to determine atomic weight, consists of 1/12 the weight of carbon-12. (Does this all sound complicated? Don't worry. Just stay with me a moment because once Henry gets here, it all becomes simpler). For now, just think of atomic weight as simply the average mass of an atom of an element which is expressed in relation to the mass of carbon-12.

You might ask, and rightly so, why didn't scientists assign the weight of carbon to be 1 since it is the substance to which everything else is being compared. Well, carbon has six protons and six neutrons so scientists, by international agreement, determined that carbon-12 has a mass of exactly 12 atomic mass units (and you thought the international community couldn't decide on anything).

Okay, now I introduce Henry Mosely, the guy I told you who would make it all simpler. Henry showed that atomic number rather than atomic weight was the most important in describing chemical properties of an element (that Henry, always trying to outdo the other guy). The atomic number of an element is equal to the number of protons in the nuclei of its atoms. Now that is a little simpler, isn't it?

Okay, now that we have that clarified, let's get back to the periodic table. First of all, the rows of elements on the table are called periods, while the columns make up element groups. Therefore, as you look at the chart from top to bottom, each line on the chart represents a family of elements (or elements with similar properties). A property is simply the characteristics of the element (how you would describe it). Any type of matter has both physical properties (i.e. color, density, specific heat, boiling temperature) and chemical properties (i.e. how the metal reacts, the amount of heat it produces).

Each element is assigned one upper case letter (the element may or may not also have a lower case letter; some are a bit greedy), but they only get one upper case letter (no matter how much they beg and how much they plead). These letters represent the elements without any indication of charge. However, there are seven exceptions to this rule (isn't there always). The exceptions are the seven elements that are in gaseous form (hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine and iodine). By the way, any time you see two or more element symbols linked together (those elements do like to snuggle), then this represents a compound.

As previously mentioned, the periodic table is read from left to right and from top to bottom. Hydrogen, found at the extreme upper left corner, is the first element on the table, and it has an atomic number of 1. This tells you that it has 1 proton. For each proton there is an electron; therefore, for hydrogen to be neutral, it must have 1 proton and 1 electron. The next element is helium which has an atomic number of 2. Look down one row and to the left, and you will find the next element, lithium, and so on. If your periodic table has different colors, the colors reflect what form the element takes at room temperature.

Hopefully you now have a basic understanding of the periodic table. If not, maybe you should step away from the video game you are playing and actually read something as your mind is starting to atrophy.


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