Position of Elements in Modern Periodic Table
There are 18 vertical columns known as ‘groups’ and 7 horizontal rows called ‘periods’ in the modern periodic table. Elements are placed based on their atomic number.

Position of Elements in Periods
The first period has only two elements hence it is the shortest period. The second and third period contains 8 elements hence these are called short periods. Fourth and fifth period has 18 elements so called as long periods. Sixth period consists of 32 elements and called as the longest period. The seventh period is incomplete period.

Position of Elements in Groups
Elements of same group have equal electrons in their outermost shell. i.e. The valence of these elements is same.
Group 1 consists alkali metals, Group 2 contains alkaline earth metals . Group 17 has halogens and Group 18 has noble gases. Noble gases has completely filled outermost shells.
Metals are arranged on left hand side of modern periodic table while non metals are arranged in right side.
Elements of the groups 1 and 2 and from 13 to 17 are called as normal elements. Their outermost shell is incomplete.
Elements of the groups from 3 to 12 are called as transition elements. These element contains two incomplete outermost shells. Elements placed at bottom of the periodic table are called as inner transition elements. There are two series of these elements “Lanthanides” and “Actinides”. Elements having atomic number between 58 to 71 are called Lanthanides. Lanthanides series starts with Lanthanum which is placed in group 3 and period 6. It is placed in group 3 because of its similar properties with group 3 elements. Elements with atomic number between 90 to 103 are called as Actinides. Actinides series start with actinium which is placed in group 3 period 7 since its properties are closely related to group 3 elements. Some elements such as boron, silicon, germanium, arsenic show properties of both metal and nonmetals, these are called metalloids.

Trends in Modern Periodic Table
Valency
Valency is the number of electrons needed to be accepted or donated so as to have a completely filled outermost shell. From left to right in periods, valence increases from 1 to 4 and then decreases to 0. In groups even though atomic number increases by order 2-8-8-18-18-32 still the number of outermost shell electrons remains same and therefore valence remains same.

Atomic Size
Atomic size refers to radius of an atom i.e. the distance from center of nucleus to outermost shell. Down the group number of shells increases hence atomic size increases. However, in a period number of shells remains same but the nuclear charge (i.e. number of protons) increases. With increased nuclear charge nucleus tend to pull electrons closer to nucleus hence size of atom decreases.

Metallic and Nonmetallic Character
In periods, from left to right, nuclear charge increases therefore the pull of nucleus over outermost shell becomes stronger. Due to which the tendency to lose electrons decreases i.e. the metallic character decreases. The same is the reason why non metallic character increases from left to right. In comparison to this, down the group as the atomic size increases the pull of nucleus over outermost shell electrons decreases, so metallic character increases and nonmetallic character decreases.

Electronegativity
In compounds formed by bonding between two or more elements, one of the element have higher tendency to attract shared electrons. The term electronegativity signifies the tendency of atom to attract the shared pair of electrons towards itself. In periods as the nuclear charge increases therefore the electronegativity also increases. However due to increase in atomic size, down the group electronegativity decreases.

Periodic Table Trends