## Modern Periodic Table

hi friends in this video we look at the

last stop in our journey the modern

periodic table remember in the previous

videos we discussed the earlier attempts

to classify elements that is the double

renews triads Newlands law of octaves

and Mendeleev spiri otic table here we

are going to look at the modern periodic

table but we are going to do it in a

different and interesting way so rather

than starting with the periodic table we

and will fill it up as we go along in

this video I'm sure by the end of the

video you'll be a master of the periodic

table and as usual we'll finish off with

our top three questions on this topic

normally when you draw a table it looks

something like this with rows and

columns but if you take a look at our

periodic table it has a strange shape

and we are going to see why as I said

are going to fill it up as we go along

in this video since our focus is only

till the 20th element which is calcium

so we'll be looking only at the first

four rows of the periodic table let's

call this our mini periodic table we

will talk about the lower rows later on

in this video so I'd like you to pause

the video here and go ahead and sketch

our mini periodic table in your notebook

just draw this blank table till the

fourth row you can also pause the video

here and do a print screen and take out

a printout of the blank table friends

table I'm going to magically shrink

myself so that you can see this table

better and let's fill up this table

together first let's start by numbering

the rows so it's going to be 1 2 3 and

so on in our mini periodic table we have

only 4 rows but the full table has seven

rows rows are called P

so these are period numbers similarly we

can number the columns so the column

number is going to be one two three and

all the way up to 18 columns are called

groups in the periodic table so these

are our group numbers there is a

different numbering scheme for groups as

well but we'll look at that later on in

the video

next start numbering the boxes so start

from one to finish the first row then go

on to the second row 3 4 5 and so on

these numbers look like serial numbers

or roll numbers but do you know what

they really are that's right they are

atomic numbers atomic number is defined

as the number of protons present in the

nucleus of an element this was the major

difference between the modern periodic

Mendeleev stable was based on atomic

mass but the modern table is based on

atomic number now you may be wondering

why because the scientist Moseley proved

that atomic number is a more fundamental

property for elements as compared to

atomic mass so the chemical properties

of elements are more related to their

atomic number than their atomic mass

next let's start filling in the elements

in our table so do you know which is the

first element with atomic number one

with just one proton in the nucleus

that's right the correct answer is

hydrogen so let's put the symbol of

hydrogen H in the first box next with

atomic number two we have helium and now

let's go down to the second row so there

we have lithium beryllium boron carbon

nitrogen oxygen fluorine and neon and I

want you to fill up all the way till

element number 20 so that is still

calcium

with every element that you filled in

here the atomic number is increasing by

one so what does that mean one extra

proton is being added in the nucleus now

how is the electron number changing what

do you think that's right the electrons

are also increasing by one because

remember an atom is neutral it has equal

number of protons and electrons and note

we are not concerned about the number of

neutrons right now now let's talk about

the significance of the period or the

row so in our mini periodic table we

have periods from 1 to 4 but remember in

the full periodic table you have it up

till 7 so what is this period number

tell us it tells us the number of

electron shells or electron orbits

present in an atom so we can predict the

number of shells without even drawing

the electronic structure so let's take

some examples hydrogen is in period one

so it has only one shell now if you look

at oxygen it's in period two so it

contains two shells so similarly how

many shells does aluminium have that's

right three shells since it's in period

3 and what about calcium correct for

shells it's in period number four so

with every new period one more shell is

being added now let's verify this by

looking at the electronic configuration

of a few elements let's draw the

electron configuration of hydrogen it

has atomic number one so just one proton

and one electron and as you can see it

has only one shell next let's look at

oxygen it has atomic number eight so

that's eight protons and eight electrons

so if you draw its electron

configuration the first shell will have

two electrons since it can hold maximum

of two and the second shell has

electrons so as you can see oxygen is in

period number two and it has two shells

next we have aluminium with atomic

number thirteen so the electron

configuration is going to be 2 comma 8

comma 3 so aluminium in the third period

has 3 shells you can draw the full

electron configuration or you can write

it in this simple common notation 2

comma 8 comma 3 and let's also look at

calcium which is in the fourth period

with atomic number 20 and as you can see

it's electron configuration is 2 comma 8

comma 8 comma 2 so as expected calcium

in the fourth period has 4 shells now

let's discuss the significance of the

group we always try to group similar

things together so that it's easy for us

a simple everyday life example is the

grocery store where you'll find similar

things grouped together for example

you'll find all the vegetables together

salt and sugar on one side and all the

chocolates in one place now imagine you

walk into the grocery store and

everything is scattered you go crazy

while shopping right similarly in the

periodic table elements having similar

chemical properties are grouped together

now let's take a closer look if you look

at Group one except for hydrogen all the

elements in Group one are metals they

are called alkali metals and they have

similar chemical properties they have

the same valency one now let's look at

Group two once again we see their metals

in this group they are called alkaline

earth metals and they also have the same

valency now let's move ahead to group 17

if you look at this group

it contains nonmetals and they have the

same valency 1 now an interesting

question is why do elements in the same

group

have same valency and similar chemical

properties what do you think well the

answer lies in how the electrons are

arranged in the atom that is the

electronic configuration so let's go

configuration of elements in the same

elements hydrogen lithium sodium and

potassium they have atomic numbers of 1

3 11 and 19 now let's try to write down

their electronic configuration hydrogen

is simple it just has one electron now

lithium has an atomic number of 3 so

it's going to be 2 comma 1 sodium will

be 2 comma 8 comma 1 and potassium is

going to be 2 comma 8 comma 8 comma 1 so

can you see what these elements have in

common that's right they have just one

electron in their outermost shell so

that's one valence electron so all these

elements have the valency 1 and why do

they have similar chemical properties

because chemical properties depend on

the number of valence electrons which is

same for all these elements now let's

look at Group two here we have beryllium

magnesium and calcium similarly let's

write down their electronic

configurations so beryllium with an

atomic number four is going to be 2

comma 2 magnesium which has an atomic

number of 12 the electron configuration

is going to be 2 comma 8 comma 2 and

calcium which has 20 electrons is going

to be 2 comma 8 comma 8 comma 2 so once

again you can see all these elements

have the same number of valence

electrons which is 2 in this case so

they have the same valency 2 and hence

they show similar chemical properties in

summary we saw that elements belonging

to the same group have the same valency

and similar chemical properties because

they have the same number of valence

electrons

now the group numbering that we saw from

1 to 18 is the new scheme there is an

older scheme that uses Roman numbers and

alphabets a and B let's take a look at

the old scheme as well as we have seen

the new scheme has group numbers from 1

to 18 now let's look at the old scheme

Group 1 has the number 1 a note 1 is

written in Roman numeral and the

alphabet capital e group 2 is two-way

now when we go to group 3 it's tricky

it's going to be 3 B then you have 4 b5

b6 b7 B and groups 8 9 and 10 have the

Roman number 8 then group 11 is 1 b12 is

2b and then when you move on to 13 it's

3 a 4 a 5 a 6 a and group 17 is 7 a and

the last group group 18 has the number 0

the new group numbering scheme is much

easier to remember than the old one but

it's important to know the old one as

well because sometimes it's used now I

can teach you an easy trick to remember

the mapping between the new and the old

scheme basically you have to calcium in

your syllabus element number 20 so if

you take a look you have Group 1 group 2

and then group 13 14 15 16 17 and 18 in

your syllabus you don't have the groups

from 3 to 12 now if you look at the old

scheme so what you have in syllabus is 1

e2 way and then 3 a 4 a 5 a 6 a 7 a and

group 0 so basically only the a groups

are in your syllabus and group 0 which

is the noble gases the B groups and

group 8 are not in your syllabus so I

hope that helps you remember the old

scheme we have a lot of details in our

periodic table now let's go ahead and

color you might have seen these colorful

pictures of the periodic table where the

colors represent the different types of

elements for example metals non-metals

noble gases and metalloids so are you

ready to start coloring our periodic

table first let's color the four broad

categories of elements metals non-metals

metalloids and noble gases

now our periodic table looks more

colorful right but you might have seen

some other periodic tables which have

more colors and some different colors in

different groups like this picture here

so let's go ahead and take a look at

some of these groups because they have

some special names the group one

elements are called alkali metals

because these form strong alkalis with

water the group two elements are called

alkaline earth metals because they form

weaker alkalis as compared to the

previous group now moving on to group

thirteen this group is called the boron

family because boron is the first member

in the group similarly group 14 is

called carbon family and then you have

group 15 as nitrogen family and group 16

is called the oxygen family or also

known as Chalco jhin's which means all

forming now group 17 is called the

halogen family and the last group group

18 are known as noble gases or inert

gases till now our focus has been from

element 1 to 20 so till calcium now

let's go ahead and take a look at the

full periodic table in the complete

periodic table we have seven periods or

seven rows and eighteen groups or 18

columns now if you look at period six

and seven you'll notice something

interesting that elements with atomic

number 57 - 71 and 89 203 are put

separately below the periodic table

this is done to compact the periodic

table the elements 57 to 71 are called

lanthanide series because they start

with the element lanthanum these

elements are rare earth elements and

elements from 89 203 are called actinide

elements now let's discuss the merits of

the modern periodic table the merits are

that it corrected the anomalies in

Mendeley its periodic table now how did

it do that because Mendeleev stable was

based on atomic mass but the modern

table is based on atomic number it's

based on the modern periodic law which

states that the properties of elements

are a periodic function of their atomic

number so let's take a look how the

anomalies of Mendeleev stable were

isotopes isotopes are atoms of an

element having same atomic number but

different mass number they have

identical chemical properties now

isotopes could not fit into Mendeleev

z-- periodic table but in the modern

periodic table they fit in nicely

because they have the same atomic number

so isotopes of an element belong in the

same position as the element and that

makes sense because they have same

chemical properties the second point is

Mendeleev had to make certain exceptions

for some elements but these are fixed in

the modern periodic table for example

the position of cobalt and nickel cobalt

should come first because it has a lower

atomic number as compared to nickel even

though it has a higher atomic mass

because the modern periodic table is

based on atomic number even though

hydrogen is placed in Group one it's

given special treatment many times it's

shown broken off from Group one now why

is that because hydrogen shows prop

that are similar to group 1 elements

that is alkali metals and also group 17

elements that is halogens so since it

shows properties of both these groups

its given special treatment friends I

hope you feel that you have mastered the

modern periodic table now remember

practice makes you perfect so I would

recommend you to draw out our mini

periodic table a couple of times and

learn the first 20 elements now trends

in the periodic table will be covered in

a separate video where we look at how

the properties change across the period

and down the group and do remember to

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