1. Number of electrons in the outermost shell
Group number is equal to the number of electrons in the outermost shell of any element.
e.g: Na Group number I - number of electrons in the outer most shell= 1
Group number 0 is also referred as group number VIII. All the elements have 8 electrons in the outer shell But He having only 2 electrons.
2. Valency of the element
Valency is the number of electrons given, taken or shared in making bonds by the elements. It is important in writing the correct formula of a compound as well. General rule that can be used to calculate the valency is as follows.
Valency of Groups I -IV
Equal to the group number
e.g : Mg= Group number II= valency= 2;
Valency of Groups IV- VII
equals to 8- group number
e.g: Cl group number 7= valency=( 8-7)= 1
Valency of Group number 0
equals to zero
3. Number of electronic shells
number of electronic shells is equal to the period number (horizontal raws)
e.g Li is in period 2 = has 2 shells with electrons
4. Reactivity
Some of the metals in group I and II and also some elements in group number III are metals. All the other elements are non metals. The usual trend of reactivity
for metals :
increases down the group. Na is more reactive than Li. K is more reactive than Na. The reason for this can be simply described as follows. Metals releases electrons to achieve the nobel gas configuration when making bonds. Releasing of electrons become more easy when the outer most shell electrons to be released is more distant from the nucleus.
for non metals
Decreases down the group. E.g Fluorine is more reactive than chlorine. Chlorine is more reactive than iodine.
11:36 PM
along periods
chemistry
GCSE
group number
groups
patterns
periodic table
periodic trends
reactivity
valency
