The Periodic Table Essay Research Paper Classification - Реферат

The Periodic Table Essay, Research Paper

Classification of Elements: The Periodic Table

Arranging The Elements:

The Russian chemist Dmitri Mendeleev uncovered evidence that consisted of a huge collection of facts

about the 63 elements that had been discovered by the mid-1800’s. His clues had to do with the physical and

chemical properties of these elements. Mendeleev was convinced that he could arrange the elements so that those

with similar properties were grouped together. Mendeleev made a card for each element including the atomic mass,

density, color, and melting point. He also included the element’s valence, bonding power. Mendeleev, looking for

patterns, arranged the card so that the atomic mass increases. If he started with lithium, the next would be beryllium.

Then would come boron, carbon, nitrogen, oxygen, and flourine. With the cards arranged in this order Mendeleev

noticed that the pattern of valences was: 1 2 3 4 3 2 1. Seven elements in a row, and a pattern of valences repeating

themselves. As he arranged all 63 cards in this manner in doing so he also saw something even more remarkable.

When the elements were arranged in this way, they fell into columns, one under the other. All the elements in one

column had the same valence and showed similar physical and chemical properties. Mendeleev designed a periodic

table in wich the elements were arranged in order of increasing atomic mass. The periodic law states that the physicaland chemical properties of the elements are periodic functions of their atomic numbers.

The periodic table of the elements is one of the most important tools of a scientist, especially a chemist.

The periodic table is a classification system, a way of organizing vast amounts of information in a logical , usable,

meaningful way. The columns the elements are placed in are called groups or families. Elements within the group

have similar but not identical properties. For example, lithium ( Li ), sodium ( Na ), potassium ( K ), and other

members of family 1 are all soft, white, shiny metals. They are all highly reactive elements, wich means

they readily combine with other elements to form compounds. In each individual square it contains the

atomic mass, atomic number, chemical symbol, and name/abbr.

There are now 109 elements in the periodic table. Most of the elements are metals. Chemical properties in metals are such things as lust and shininess. Most metals also allow heat and electricity to move through them easily. Therefor metals are good conductors of heat and electricity. In general metals have high density. This means they are heavy for their size. There are two other physical properties that are common to many metals. Most metals

are ductile, wich means they can be drawn out into thin wires. And most metals are malleable, wich means

they can be hammered into thin sheets. The chemical properties of metals are not as easily observed as

the physical properties. The chemical properties of any element depend of the electron arrangement in

the atoms of the element. An atom of a metal can have 1, 2, 3, or 4 electrons in its outermost energy level.

The electrons in a metals outermost energy level are held together weakly. So metals are elements that tend

to lose their outermost energy levels electrons when they combine chemically. Because they tend to lose

electrons, most metals will react chemically with water or oxygen in the atmosphere. This usually results

in corrosion. Corrosion is the gradual wearing away of a metal due to a chemical reaction in which the metal

element is changed into a metallic compound. Tarnishing is a nother example of corrosion. This results when

silver reacts with sulfer in the air or in certain foods.

Properties of nonmetals have no luster and are dull in appearance. Nonmetals do not conduct heat

and electricity very well. Nonmetals are brittle and break easily. They cannot be drawn out into wire or

hammered into thin sheets. Nonmetals are neither ductile nor malleable. Nonmetals usually have lower melting

points and densities than that of metals. Nonmetals are not easy to recognize as a group as metals are.

Atoms of most nonmetals are 5, 6, 7, or 8 electrons in the outermost energy level. Atoms with 5, 6,

or 7 electrons gain 3, 2, or 1 electron, respectively when they combine chemically. Nonmetals are elements

that tend to gain electrons. When you look at the dividing line between metals and nonmetal you see the

metalloids. Metalloid means metallike. All metalloids are solid that can be shiny or dull. They conduct heat

and electricity better than nonmetals but not as well as metals. Metalloids are ductile and malleable. The metalloids include boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine.

Chemical families are elements that have similar properties because they have the same number

of valence electrons. The elements in family one are called the alkali metals, with the exception of hydrogen.

The alkali metals are soft, siver-white, shiny metals. They are so soft they can be cut with a knife. Alkali

metals are good conductors of heat and electricity. The reaction is violent when the alkali metals combine with

water and oxygen. Family two consists of the alkali-earth metals. These metals are never found in nature as

uncombined metals. Instead they exist bonded with other metals as compounds. Another kind of metal that

is hard to label into a group or family is the transition metals. Transition metals have properties similar to other

metals. Transition metals are good conductors of electicity as well. An interesting transition metal is mercury.

Murcuy is a liquid metal at temperatures above -38 degrees celcius. Most transition metals have 1 or 2 valence

electrons. When they combine with of atoms, they lose either 1 or both of their valence electrons. The compounds

of transition meteals are usually brightly colored and are often used to color paint.

ALKALI METALS ALKALINE-EARTH METALS TRANSITION METALS

Lithium (Li) Beryllium (Be) Iron (Fe) Zinc (Zn)

Sodium (Na) Magnesium (Mg) Cobalt (Co) Cadmium (Cd)

Potassium (K) Calcium (Ca) Nickel (Ni) Mercury (Hg)

Rubidium (Rb) Strontium (Sr) Copper (Cu)

Cesium (Cs) Barium (Ba) Silver (Ag)

Francium (Fr) Radium (Ra) Gold (Au)

To the right of the transition elements are six families, five of them contain some metalloids. Family

thirteen is the boron family. Atoms of this family usually have three valence electrons. Family fourteen, the

carbon family, usually have four valence electrons. The nitrogen family, family fifteen, is named after an element

that makes up 78% of the air around you: nitrogen. The atoms of elements in this family have 5 valence elctrons

in their outermost energy level. These atoms tend to share electrons when they bond with other atoms. The elements

that make up family sixteen are called the oxygen family. Atoms of these elements have six valence electrons. Most

elements in this family share electrons when forming compounds. Family seventeen is the halogen family. The elements of this family have seven valence electrons. Atoms of these elements only need to gain one electron to fill

their outermost energy level. The last family, the noble gases, are normally unreactive. Under special conditions, certain noble gases can combine chemically with other elements. Because they do not readily form compounds with other elements, the noble gases are sometimes called the inert – gases.

Certain properties of elements vary in regular ways from left to right across a period. These properties include electron arrangement, reactivity, atomic size, and metallic properties. The valence number of an elements is related to the electrons in the ourter most energy level of an atom of that element. It is these electrons that are involved in the chemical combining of elements to form compounds.

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