Lecture No.7 The Periodic Table and Some Properties of The Elements Lecturer: Amal Abu-Mostafa

Session Objectives: Dmitri Mendeleev’s Periodic Table (1869). A better arrangement. Arrangement of the Modern Periodic Table. Groups in Periodic table (P.T). Metals, Nonmetals, and Metalloids

The Periodic Table (PT) and the Elements What is the periodic table ? What information is obtained from the table ? How can elemental properties be predicted base on the PT ?

Dmitri Mendeleev’s Periodic Table (1869): The need for organizing the elements was recognized by many early chemists. Chemists used the properties of elements to sort them into groups. The periodic table we use today is based on the efforts of a Russian chemist, Dmitri Mendeleev and a German physicist, Lothar Mayer in 1869. Dmitri Mendeleev could not make a complete table, only had 63 elements leaving many spaces between elements for undiscovered ones.

Dmitri Mendeleev arranged elements in order of increasing atomic mass. Thus, the first “Periodic Table”

A better arrangement: Later, Henri Moseley ( England,1887- 1915) established that each element has a unique atomic number, which is how the current periodic table is organized. It is the arrangement used today.

Arrangement of the Modern Periodic Table: It is the arrangement of elements in order of increasing atomic number with elements having similar properties placed in vertical groups or columns.

The Horizontal rows in the table are called = periods. There are 7 periods, Identified by numbers. Below the main body of the table are two long rows of 14 elements each. These actually belong in the main body of the table following La (Z=57) and Ac (Z=89), they are almost always placed below simply to conserve space. Rows in P.T having many elements arranged according to the increase in atomic number. Elements in periods don’t have similar properties.

The vertical columns in the periodic table are called = groups (or families). Having elements with similar properties. Identified by number & letter, the groups are labeled 1A to 8A . And the shorter groups are labeled 1B to 8B. In some texts, groups are identified with Roman numerals; Group 3A IIIA. For example, Hydrogen is in period 1 and group 1, first element in periodic table because its atomic number is 1.

The elements in the longer columns (the A group) are known as the main group elements or (Representative). Those that fall into the (B groups) in the center of the table are called transition elements.

The elements in the two long rows below the main body of the table are the inner transition elements (rare elements), and each row is named after the element that it follows in the main body of the table. Thus, elements 58 – 71 are called the lanthanide elements, because they follow La (Lanthanum, Z= 57). And elements 90 – 103 are called actinide elements, because they follow Ac (Actinium, Z= 89).

Periodic Table: The three broad Classes Main, Transition, Rare Earth

Groups in Periodic table (P.T) 1) Alkali metals 1A or (IA): Consist of: Li, Na, K, Rb, Cs, and Fr. Except H. They are similar in physical and chemical properties. All of them are metals, solid, react with water to produce hydroxide, so they are strongly alkaline that’s why called alkali metals. 2 Na + 2 H2O 2 NaOH + H2

2. Alkaline earth metals 2A or (IIA) Consist of Be, Mg, Ca, Sr, Ba, and Ra Ca + 2 H2O Ca(OH )2 + H2 The Group 2A elements are also metals. They also form bases with water; do not dissolve well, hence “earth metals” 3. Halogens 7A or (VIIA) : Consist of F, Cl, Br, I, and At (non metals) Halogens, derived from the Greek word meaning (sea or salt).

4. Noble gases 8A or (VIIIA): Consist of He, Ne, Ar, Kr, Xe, and Rn (non metals). The term noble is used when we wish to suggest a very limited degree of chemical reactivity. Hydrogen: The hydrogen square sits at the top of Family 1A, but it is not a member of that family. Hydrogen is in a class of its own. It’s a gas at room temperature. It has one proton and one electron in its one and only energy level. Hydrogen only needs 2 electrons to fill up its valence shell.

Metals, Nonmetals, and Metalloids

Metals, Nonmetals, and Metalloids

Metals, Nonmetals, and Metalloids A metal has a characteristic luster, or shine. Metals are good conductors of heat and electricity. Except for mercury, the metallic elements are solids at room temperature (about 20°C). Metals are malleable (can be hammered into sheets) Metals are ductile (can be stretched into thin wires). A chemical property of metal is its reaction with water which results in corrosion.

Nonmetals: Nonmetals lacks the characteristic appearance of a metal. Most of the nonmetals are gases (for example, chlorine and oxygen). The solid nonmetals are usually hard, brittle substances, (for example, phosphorus and sulfur). Bromine is the only liquid nonmetal. Non-metals are poor conductors of heat and electricity. Non-metals are not ductile or malleable. They are dull. Sulfur

Metalloids or semimetals : A metalloid, or semimetal, is an element having both metallic and nonmetallic properties. Metalloids are solids that can be shiny or dull. They conduct heat and electricity better than non-metals but not as well as metals (semiconductors). They are ductile and malleable These elements, such as silicon (Si) and germanium (Ge), are usually good semiconductors. Silicon

Note: In the periodic table we have 118 elements, 92 of them are found naturally on Earth, and the rest are synthetic elements that have been produced artificially.

Thank you