Modern Periodic Table

                                                the periodic table put forth by

Mendeleev was quite well defined but it

wasn't the best table ever 

why do I say

so

it's because with time the number of

elements being discovered increased and

fitting them into the table according to

the periodic law by Mendeleev seemed

difficult also we have taken a look at

the major limitations of the periodic

table by Mendeleev so with all these

limitations how do we study the elements

how do we carry out the periodic

classification well if the elements

discovered later did not follow the

periodic law given by Mendeleev then the

only way to arrange them was by

modifying the law yes this was however

not what scientists could think of as

the first step it was quite gradually

that the scientists realized the fact

that the law could be modified but how

did this happen it was around 1913 that

the British physicist Henry Moseley

found an interesting fact he realized

that instead of atomic mass all the

elements will show periodicity if

arranged on the basis of the atomic

numbers wait a second did I just say

atomic number isn't atomic number a

randomly assigned number to the atom by

us actually not atomic number of any

element is never a randomly assigned

number it is basically the number of

protons present in the nucleus of the

atom of that element for instance let us

consider the first four elements in the

table so we get atomic numbers of

hydrogen as one helium as two lithium as

three and beryllium as four so why are

these elements assigned these particular

atomic numbers only can be changed these

numbers ever no we can't that is because

they have these respective numbers of

protons in their nuclei hydrogen has

just one proton in its nucleus

similarly helium has two and lithium has

three and how many protons will Beryl

has correct it has four protons the same

is valid for other elements as well

coming back to the table did Henry

Moseley think that characteristics of

elements are based on their atomic

numbers and not the atomic masses yes

that's what he meant and with this there

emerged a new law of studying the

periodicity of elements it was called

the modern periodic law

the law stated that the properties of

elements are periodic functions of

atomic numbers so what does this mean

this means that the physical and

chemical properties of elements do occur

periodically but this happens when the

elements are arranged according to their

atomic numbers all the known elements

could be arranged based on their atomic

numbers with this predicting the

properties of elements yet to be

discovered but simpler and more precise

this helped in placing the newly

discovered elements properly in the

periodic table also overcoming the

limitations of Mendeleev stable was

another advantage and how did that

happen do you remember their limitations

the first limitation of no precise

position for hydrogen was mainly

overcome it was assigned a position that

would not lead to any confusion we will

take a detailed look at this position of

hydrogen later in the higher grades next

limitation of the Mendeleev stable was

the position of isotopes can you

recollect what isotopes are yes they are

the atoms of the same element with

different number of neutrons that is the

reason why in spite of belonging to the

same element the atoms have different

atomic masses because atomic mass is the

sum total of all the protons and

neutrons present in the nucleus placing

isotopes in the table was a limitation

but as we know in the modern periodic

table the position of elements was no

longer based on atomic masses they were

based on atomic numbers an atomic number

is given by the number of protons that

means

a different number of neutrons will not

be a worry for us so it was possible to

place the isotopes now because all the

isotopes of any particular element could

be placed at one single place and this

place would be the position of that

element in the table so now can we say

that chlorine-35 and chlorine-37 will be

placed together they both have 17

protons which means they will have the

same atomic number hence they will be

placed together lastly we have the

prediction and placement of undiscovered

elements the previous table by Mendeleev

was based on atomic masses of elements

however the atomic masses of elements

were not arranged in a constantly

increasing order hence if newly

discovered elements were to be placed in

the table then their position would be

confusing but why it's simply because if

the atomic masses of previously

discovered elements were not in a

regularly increasing manner then how and

where will be placed the new ones just

for the sake of understanding let us

assume some values for the atomic masses

of two elements element one has atomic

mass three hundred whose position comes

first

while element two has an atomic mass 297

which is placed later in the table that

is after element one now in this case if

a newly discovered element the element

three has atomic mass of 299 where will

we place it between the two elements or

after the second element with atomic

mass 297 and this is what was happening

with mental layoffs periodic table

because the atomic masses of elements

were not placed in a constantly

increasing manner some elements did have

atomic masses less than the previously

placed element so placing the newly

discovered elements will disturb the

entire table but in the modern periodic

table the position of elements was based

on atomic numbers so newly discovered

elements could be easily added in

between because the atomic numbers of

are found to occur in a constantly

increasing manner this is how the

important limitation of mental layoffs

periodic table but ruled out and that is

the reason why the new periodic table

surfaced as the most useful tool for

studying elements the newly arranged

table of elements was based on the

modified law do you remember the name of

this important law yes it is the modern

periodic law so can you guess the name

of the table that was based on the SLO

yes it was called the modern periodic

table now let's have a detailed look at

this modern periodic table its

properties.