The Third Law You Should Know

In this installment of the Laws You Should Know is Mendelev's Periodic Law. Elements are the essential blocks to our world microcosm and macrocosm worlds. Each element has its own spirit entity. Every substance in the universe has a composition of individual elements. We are merely saying elements have their own character

The elements have atoms that can be the same but different from the atoms of every other element. What creates the difference is that each element have their own particular atomic weight as John Dalton showed, and that each element has its own unique set of properties. Chemists in 1860 identified and studied sixty-plus different elements. They noticed each element has similarities to some of the other elements.

How are elements similar? There are elements that are gases, and others are metals. Some are extremely reactive like hydrogen, oxygen, sodium, and chlorine. They have a rapid chemical reaction when combined. You would not find some of these on earth in their uncombined pure form. We have gold, platinum, and nitrogen that are more inert. They don't combine as easily with other elements. The aforementioned elements are found here on earth in their elemental form like gold nuggets or nitrogen gas.

Nature has its patterns. As more elements being discovered it looks as if the elements would have some sort of pattern. First we looked at the atomic weight. Remember Dalton showed the atoms of different elements are different in weight? We calculated the atomic weight of each element. Thank God for oxygen being a very common element that combines with most other elements, and it became the standard measure of weight. All elements were weighed by comparing them to the weight of oxygen. Now it became easy for all the known chemical elements could then be arranged in order by weight. Now chemists were able with confidence to examine the physical and chemical properties of the elements, hoping to find a pattern. The chemical properties were paramount in the search for patterns. At that time of the known elements they react with other elements to form compounds. We found each element combines with others only in certain ways.

Now chemists gave each element a particular combining number, or valence, passed on how it joins with other elements. The following examples are one oxygen will combine with two hydrogen atoms to form water. Each hydrogen atom has a valence of 1 and the oxygen atom has a valence of 2. The result is one oxygen atom can combine with two hydrogen. One atom of oxygen will combine with one atom of calcium to form calcium oxide. You can visualize the picture of the calcium atom , like the oxygen, must have a valence of 2.

How do we form ammonia? We will put one nitrogen atom combine it with three hydrogen atoms, and "Whaa La!" We know each hydrogen atom has a combining power of 1, then nitrogen's valence must be 3. Here are the 18 elements known in 1860 by weight, and their valence.

Element - Valence

Hydrogen - 1
Lithium - 1
Beryllium - 2
Boron - 3
Carbon - 4
Nitrogen - 3
Oxygen - 2
Fluorine - 1
Sodium - 1
Magnesium - 2
Aluminum - 3
Silicon - 4
Phosphorus - 3
Sulfur - 2
Chlorine - 1
Potassium - 1
Calcium - 2
Titanium - 3

The valence is only one of many properties each element has. Finely all properties found a fit into a simple pattern. Our great minds thought of different numerical arrangements to form a pattern. Some elements didn't fit the pattern properly. By 1866, John Newlands thought the elements should follow a pattern like a musical scale. The combining numbers, or valences, seemed to repeat themselves in groups of seven. Newland's published chart of elements arranged in this pattern worked well for the lighter elements, but fell apart with the heavier elements. Newland came close but no cigar!

In 1869, a Russian chemist Dmitri Mendeleyev, at last won the honor of discovering the pattern of the elements. He realized the valence of the elements are the most important chemical property. The valences shows exactly how each element reacts with all other elements. Mendeleyev arranged the elements according to their atomic weight, followed by their valences. when he group the elements this way he discovered that their chemical and physical properties showed a periodic or repeating pattern.

The other great minds were looking for a "magic number" like the magic number of 9* (which will be explained latter) the elements that repeated again and again through the list of known elements. Mendeleyev didn't try to force the issue into a regular numerical pattern. He got to the fourth repetition of the periodic cycle and found a large number of elements in the list having a valence of 3. Now he made the period longer. The "extra" elements all had to be included before the cycle continued. The same thing occurred for the fifth period, and the sixth period. Mendeleyev reasoned by grouping the elements by their properties, rather than any particular number, he simply widened his chart to make room for the additional elements that belonged in those groups. This discovery is now Mendeleyev's Period Law:arrangement in order of atomic weight, the elements periodically repeat similar physical and chemical properties.This is known as the periodic law. Mendeleyev's chart of the elements, shows this repetition of the properties, is known as the periodic law. The chart is the most complete statement of Mendeleyev's law.

Move from left to right and down the page, the elements are in order by atomic weight. Each row across the page is called a period. Each period is one complete repetition of similar chemical and physical properties. Each column of elements in the table is a group of elements with similar properties. We call these groups of elements families of elements. The elements in the left most column are the alkali metals family. The family members are hydrogen, lithium, sodium, potassium, rubidium, and cesium. They are metallic. Hydrogen acts like a metal at very low temperatures. They all have a valence of 1. these elements are chemically active, except for hydrogen gas, and are never found on earth in their pure form. Note these elements are always combined with other elements in compounds. the second column has another group of metals, known as the alkaline earth metals. They have a valence of 2. these are also reactive, but not so reactive as the elements in the first column.

The last column, has a family of elements known as halogens. The halogens are non metals that are very chemically active. Fluorine is the most reactive element of all. It is so reactive and almost impossible to produce and keep in its elemental form. It will react with glass! The halogens include the elements chlorine, bromine, and iodine. Their valence is 1 and react strongly with metals. They have strong, unpleasant odors, and are quite poisonous.

Mendeleyev arranged the elements by their properties, and found several places where an element seemed to be missing. He knew where the missing elements belonged. So he mad a prediction that the four new elements would be found. If found, they would prove that Mendeleyev's periodic law was correct.

In 1874, five years after Mendeleyev first published his periodic table, the first discovery was made. A French chemist found a missing element. It was named gallium. Its atomic weight and physical and chemical properties matched Mendeleyev's prediction.

The second and the third soon followed, but the fourth element wasn't found until 1937. It was named technetium, because it was produced in a laboratory. Technetium is radioactive and quickly decays into other elements. It's lifetime is short and no longer exists naturally on the earth. It does exist. Mendeleyev's prediction had all proved true.

How did the elements follow this periodic pattern, after fifty years of Mendeleyev's discovery? The laws that describe the structure of atoms is known as the principles of quantum mechanics, explain why the elements form groups with similar properties. The family of gases was found in the late 1800s. these gases were difficult to find because they didn't react at all with other elements. The family consists of Helium, argon, neon, krypton, xenon, and radon.

Other large groups were found and they fit nicely into the pattern that Mendeleyev found. Mendeleyev found his niche with the chemical properties of elements. The current periodic table includes 115 elements. They all follow Mendeleyev's periodic law. Mendeleyev found the niche for others to complete the periodic table.

*This can go up to 9 digits: take any three digit number, now reverse that number then add and subtract it. Now reverse the number and add. You will always get 1089.