Dmitri Mendeleev- Successfully coined the first periodic table in year
1869. arrange the element according to the increasing order of
Relative atomic mass. Left empty spaces for elements that not found
yet at that time.
H.J.G. Moseley- carried out X-Ray analysis and confirmed that the
Proton number is the identity of each element. He confirmed that the
proton number and not the relative atomic mass that causes the
periodicity of the properties Of the elements. Established the Modern
The arrangement of elements in vertical column called Groups and horizontal rows called Periods in order of increasing proton number
There are 18 Groups numbered 1-18 and 7 Periods numbered 1-7 in a Periodic Table.
MODERN PERIODIC TABLE
Periods & Groups
7 numbered periods:
Period 1 : 2 elements, H and He.
Period 2 : 8 elements, Li to Ne.
Period 3 : 8 elements, Na to Ar.
Period 4 : 18 elements, K to Kr,
(including First transition elements)
Period 5 : 18 elements, Rb to Xe,
(including Second transition elements)
Period 6 : 32 elements, Cs to Rn,
(including Third transition elements &
Period 7 : variable no of elements, Fr to Mt,
(including Fourth transition elements &
Across the period from left to right
Proton number increases
Element become non-metallic
Oxides become more acidic
Shared similar chemical properties (have same
number of valence electrons).
Have the same number of outer shell electron
Form ion with the same charge
Form the same number of bonds
Form compound with similar formula
Special names for some groups of elements :
Group I (IA) : alkali metals
Group 2 (IIA) : alkaline earth metal
Group 17 (VIIA) : halogens
Group 18 (VIIIA) : noble gases
Classification of the Elements
classification into different block (s,p,d,f)
Valence electrons : Outer electrons of an atom, which are those involved in chemical bonding
Electron configuration : tell us how the electron are distributed among the various atomic orbital's)
based on selected physical properties of the element
Found in group 1 of the periodic table (formerly known as group IA),
very reactive metals that do not occur freely in nature.
Have only one electron in their outer shell. Therefore, they are ready
To lose that one electron in ionic bonding with other elements.
The alkali metals are softer than most other metals. Cesium and
Francium are the most reactive elements in this group. Alkali metals
can explode if they are exposed to water. The Alkali Metals are:
CLASSIFICATION BASED ON ELECTRON CONFIGURATION
Alkaline earth metal
Metallic elements found in the second group of the periodic table.
All alkaline earth elements have an oxidation number of +2, making them very reactive. Because of their reactivity, the alkaline metals are not found free in nature.
The Alkaline Earth Metals are:
Five non-metallic elements found in group 17 of the periodic table.
Have 7 electrons in their outer shells, giving them an oxidation number of -1.
The halogens exist, at room temperature, in all three states of matter:
Solid- Iodine, Astatine
Gas- Fluorine, Chlorine
The Halogens are:
The six noble gases are found in group 18 of the periodic table.
Have completely filled outer shell (8 electrons)
Except for Helium, the valence electron is 2
The noble gaseous are:
CLASSIFICATION INTO METALS, METALLOIDS AND NON-METALS
Elements from top of Group 13 (B) to the bottom of Group 16
(Po) separates the elements into 3 classes
Most metals elements exhibit the shiny luster
Metals tend to lose valence electron during chemical
change, forming positive ions called cations.
Elements in groups 14-16 of the periodic table.
Not able to conduct electricity or heat very well.
Exist in two of the three states of matter. At room temperature: gases (such as oxygen) and solids (such as carbon).
They have oxidation numbers of ±4, -3, and -2.
The Non-Metal elements are:
Elements found along the stair-step line that distinguishes metals from non-metals.
This line is drawn from between Boron and Aluminum to the border between Polonium and Astatine.
Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are semi-conductors. This means that they can carry an electrical charge under special conditions. This property makes metalloids useful in computers and calculators