The atomic number always represents the number of protons in an
element, and that never changes. It's what differentiates elements from
each other.
Atomic number is Z = Number of protons.
Atomic number increasing means number of protons increase. oxygen atomic number is 8 ,if it loose one proton means it will become nitrogen ,if it gain one proton means it will become Florine.
Atomic weight:
Atomic weight is equal to number of protons and number of neutrons.
Atomic weight A= Protons number +neutrons number.
The relationship between Number of protons and number of neutrons:
Protons number and neutrons number are equal in lighter elements p/n =1:1 , neutron number is more in heavier elements p/n=1:1.5 . the stability of the nucleus of an atom and there is a set ratio of Protons to neutrons that make the nucleus stable,
The relationship between Number of protons and number of electrons
Now the number of electrons is equal to the number of
protons in a neutral atom of an element. If it's an ion, or has any sort of positive or negative charge, then the number of electrons is equal to the number of protons plus or minus any electrons depending on the charge.
Periodic table
The modern periodic table divided into two main categories:
1)vertical columns called as Groups.
2)Horizontal columns called as Periods.
Periods :
7 period are present , the number of valence shell remains
the same for all elements and the number of electrons in the
valence shell increases from left to right.
| Period | Valence shell | Type of Period | Number of elements | Atomic Number of elements |
|---|---|---|---|---|
| 1st Period | n = 1 | Short period | 2 | Atomic number 1 and 2 |
| 2nd Period | n = 2 | Short period | 8 | Atomic number 3 to 10 |
| 3rd Period | n = 3 | Long period | 8 | Atomic number 11 to 18 |
| 4th Period | n= 4 | Long period | 18 | Atomic number 19 to 36 |
| 5th Period | n = 5 | Long period | 18 | Atomic number 37 to 54 |
| *6th Period | n = 6 | Long period | 32 | Atomic number 55 to 86 |
| *7th Period | n = 7 | Incomplete | 23 | Atomic number 87 to 109 |
Groups : 18 groups are present. Here
-1,2 and 13,14,15,16,17,18 comes under A group.
- 3 to 12 are comes under group B.
Depending upon valency electrons in orbitals
elements are divided in to s block,p block, d
block and f block.
A1 and A2 are s block elements
B3 to B12 are d block elements.
A13 to A18 are p block elements.
Lanthanides (57 to 71) and Actinides(83 to 103) are f
block elements.
These are further sub-divided into A
and B (groups I to VII), VIII group and zero group.
Member of the same group have similar electronic configuration of the valence shell and similar chemical behavior.
Groups IA and IIA are strongly metallic and are called
as 'alkali metals and alkaline earth metals'.
Transition Metals
The Transition Metals range from groups IIIB to XIIB on the periodic table. These metals form positively charged ions, are very hard, and have very high melting and boiling points. Transition metals are also good conductors of electricity and are malleable.
The VIIA family is made up of the halogens. They all tend to gain a single electron in reactions. Important members in the family include chlorine (Cl), used in making table salt and bleach, and iodine (I).
The VIIIA family is made up of the noble gases. These elements are very nonreactive.The noble gases are also called as the inert gases.
Left to right:
1.In periodic table atomic number increases left to right.
2.Atomic radii decreased from left to right because ,atomic number increase means proton number increase this charge more effective than charge of electron because of increased number of shells.
( note:the
distance of the electron from the protons in the nucleus proportional
to the attraction. If so, does this mean that no matter how many shells
you add, the attraction of the electron the nucleus is always constant,
as although the nucleus is gaining much more positive charge, the outer
electron is moving further away in each Principle Quantum Shell.effective
charge is to take the number of protons of the nucleus and subtract the
average number of electrons between the nucleus and valence electron.)
3.Electronegativity increases from left right because,right side elements has more than half of the electrons that means they spend less energy to gain electron.
4.Ionization energy decreases from left to right.
the energy required to remove an electron from a neutral atom in its
gaseous phase. Conceptually, ionization energy is the opposite of
electronegativity.
5.Electron affinity increases left to right: atoms become smaller as the forces of
attraction become stronger. This causes the electron to move closer to
the nucleus, thus increasing the electron affinity from left to right
across a period.
6.Metallic characteristics decrease from left to right across a period.this is due to decrease in radius.
In periodic table elements in left side are metals except Hydrogen.Metallic characters decreases towards right side, like semi metals,non metals halogens and inert gases.
Metallic characters:Generally, metals tend to lose electrons to form cations. Nonmetals tend to gain electrons to form anions. They also have a high oxidation potential therefore they are easily oxidized and are strong reducing agents. Metals also form basic oxides; the more basic the oxide, the higher the metallic character.
Top to Down
1.In periodic table atomic number increases top to down.
2.Atomic radius increases from top to down
3.Ionization energy decreases moving from top to down
4.Electron affinity decreases moving from top to down because a new electron would be further from the nucleus of a large atom.
5.Electronegativity decreases as atomic number increases, as a result of increased distance between the valence electron and nucleus
