Lecture No.7 The Periodic Table and Some Properties of The Elements

Lecturer: Amal Abu-Mostafa

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

Session Objectives:

What is the periodic table ? What information is obtained from the table ? How can elemental properties be predicted base on the

PT ?

The Periodic Table (PT) and the Elements

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’s Periodic Table (1869):

Dmitri Mendeleev arranged elements in order of increasing atomic mass.

Thus, the first “Periodic Table”

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.

A better arrangement:

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.

Arrangement of the Modern Periodic Table:

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

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

Groups in Periodic table (P.T)

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:

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.

Metals, Nonmetals, and Metalloids

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.

Nonmetals:

Sulfur

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.

Metalloids or semimetals :

Silicon

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.

Note:

Thank you