Chemistry Subject code: 5913 Modern Periodic Table Prepared BY SAHANA AKHTER ALAM Lecturer Chemistry Graphic Arts Institute, Dhaka

Part I Introduction. Periods and groups. Metals, nonmetals and metalloids.

The Modern Periodic Table The Periodic Table is a listing of all the known elements. The elements are organized by: Atomic number Chemical Properties

Groups and Periods Group( or Family): a vertical column. Elements in groups have similar chemical properties. Period: a horizontal row.

Groups and Periods are numbered. There are 7 periods. There are 18 numbered columns.

Metals, Nonmetals and Metalloids Elements can be classified into: Metals Nonmetals Metalloids (semimetals)

The periodic law of Elements Mendeleev discovered that the physical and chemical properties of the elements occurred in a regular repeating pattern—the Periodic Law.

Nonmetals Metals Metalloids

Actinides and Lanthanides

The Alkali Metals – Group IA Na K Rb Cs Fr H The Alkali Metals are found in the first group of the Periodic Table. They are a group of elements that are so reactive that they are always found combined with other elements in nature. The reason that these elements are so reactive is that they only have one electron in their outer shell, which they lose when bonding with other elements, to get a full outer shell of electrons. The alkali metals form +1 ions. Alkali Metals are malleable and ductile, good conductors of heat and electricity, but are very soft. The alkali metals include Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium. Alkali metals can explode when in contact with water. Cesium and Francium are the most reactive in this group. Francium is the most reactive of all metals. Although Hydrogen is a nonmetal, it is often listed with this group because it has one electron in its only energy level. Hydrogen is highly reactive but only forms covalent bonds.

The Halogens All members of the Halogen Group have seven electrons in their outer energy level. They are the seventh group on the Periodic Table. This group contains four nonmetals and one metalloid. There are no metals among the halogens. Because they only need one electron to complete their outer energy level, they are the most reactive of the nonmetals. They gain one electron and form -1 ions when bonding ionically. Fluorine is the most reactive nonmetal and is never found alone in nature. It is a poisonous greenish-yellow gas at room temperature. Fluorine compounds are added to many water systems because they prevent tooth decay. Teflon is a fluorocarbon compound. Chlorine is not as reactive as fluorine, but is also a reactive poisonous greenish-yellow gas. One of its most common compounds is NaCl, table salt. Bromine is a reddish-brown liquid at room temperature. It is often used to disinfect hot tubs. Iodine is a solid at room temperature that turns to a purple gas when heated. It is needed in your diet to keep your thyroid gland functioning properly. Astatine is a radioactive metalloid, but not much is known about its properties. F Cl Br I At

He Ne Ar Kr Xe Rn The Noble Gases The noble gases are the eighth group on the Periodic Table, and all of the members of this group are unreactive because their outer electron shell is already full.

Limitations of Periodic Table 1.Anomalous position of hydrogen:-The positon of hydrogen in the periodic table is controvertial.

2.Position of isotopes:-Since elements are arranged in increasing order of atomic masses isotopes should be placed at different positions. The isotopes of an element have same chemical properties, therefore they should be placed in same position in periodic table.Thus position of isotopes is anomalous.

3.Anomalous position of some pairs of elements:- Although the elements in the periodic table are arranged in increasing order of their atomic mass, in some cases elements with higher atomic mass is kept before the atom with lower atomic mass.Eg:- Co ( At.Mass 58.93 is placed before Ni(At Mass58.71) Te(At Mass 127.6) is placed before I ( At Mass 126.9)

4.Similar elements placed separately:-Li , Na K,Rb and Cs present in IA are quite different from coinage metals Cu ,Ag Au present in IB.

5.Dissimilar elements placed together:-Cu and Hg with many similar properties but Cu is placed in IB while Hg is placed in Group II B

. 6.Uncertianty in prediction of new elements:- It was not possible to predict how many new elements could be predicted between two elements especially among heavier elements where difference in atomic mass is high.