The periodic table arranges elements based on their proton number and electron configuration. Elements are organized into groups which have the same number of electrons in their outer shell. The periodic number indicates the number of electron shells. Group 1 elements like hydrogen, lithium and sodium have 1 electron in their outer shell. They are highly reactive metals that lose electrons to form cations. Group 2 elements such as magnesium, calcium and barium have 2 outer electrons and are less reactive alkaline earth metals. Group 7 elements like fluorine, chlorine and bromine are halogens that gain electrons to form anions.

1. THE PERIODIC TABLE
PROTONS, ELECTRONS AND PERIODIC TABLE

3. PROTON, ELECTRON AND PERIODIC TABLE.
• PROTON NUMBER/ATOMIC NO. (Z) – THIS IS THE NUMBER OF PROTON PRESENT IN
THE NUCLEUS OF AN ATOM . IN A NEUTRAL ATOM THE NO OF PROTON IS EQUAL TO
THE NO OF ELECTRON.
• Eg. Proton no of Sodium atom is 11. This also means that there are 11 electrons
present in a sodium atom.
• Proton no. of Hydrogen atom is 1, so it has only 1 electron in it.
• The identity of an element depends upon the proton no only and not upon the no of
neutron. like the element having 6 proton is going to be carbon only irrespective of
the no. of neutron present in its nucleus.

5. ELECTRONIC STRUCTURE
• DISTRIBUTION OF ELECTRONS IN VARIOUS SHELLS IS KNOWN AS ELECTRONIC
STRUCTURE.
• Eg proton no of hydrogen is 1,hence its has only 1 electron in it. The electronic
structure of Hydrogen is like this
• H - 1
• proton no of carbon is 6,hence it has 6 electrons. The electronic structure of
carbon is like this
C – 2 +4
similarly electronic structure of sodium/Na is 2+8+1 as it has 11
electrons/protons in its atom.

6. ELECTRONIC STRUCTURE AND POSITION OF
ELEMENTS IN THE PERIODIC TABLE
• GROUP NO IS EQUAL TO THE NO OF OUTERMOST ELECTRON.
H – 1
Li – 2+1
Na 2+8+1
These all elements are present in group 1 as there outermost electron no is 1.
THE PERIOD NO IS EQUAL TO THE NO OF SHELLS THAT THE ATOM OF ANY ELEMENT
CONTAINS
Eg
Hydrogen is present in period 1, Li is present in period 2 and Na is present in period
3.

7. GROUP 1
• H, Li, Na, K , Rb, Cs, and Fr are the elements present in group 1.
• Except hydrogen all are metals known as Alkali metal.
• These are highly reactive hence are kept in kerosene oil
• Readily loses 1 electron to form positive ions(cation)
• Reactivity increases down the group.
• Have low mp, decreases down the group.
• bp , density etc also decreases down the group.

8. GROUP 2
• Be, Mg, Ca, Sr, Ba and Ra are the elements present in this group.
• These are called alkaline earth metal.
• These are light metals.
• They have 2 electrons in their outermost shell that they lose to form cations.
• Be -2+2
• Mg – 2+8+2
• Reactivity increases down the group as it gets easier to lose outermost electron due to bigger
size of atom
• Mp, bp , density etc also decreases down the group.

9. GROUP 7
• F , Cl , Br, I and At etc are the elements present in group 7.
• These are commonly known as halogens .
• They have 7 electrons in their outermost shell.
• They gain 1 electron to form an anion so they are non metals.
• They are diatomic ie two atoms make a group to form a molecule. They are
written as F2,Cl2 etc
• These are highly reactive elements reactivity decreases down the group as the
size increases and distance from the nucleus