ATOMIC STRUCTURE, FUNDAMENTAL PARTICLES, Atom is the unit of matter. Atoms consist of a number of fundamental particles

 

ATOMIC STRUCTURE

 

FUNDAMENTAL PARTICLES

Atom is the unit of matter. Atoms consist of a number of fundamental particles, the most important of which are electrons, protons and neutrons. Protons and neutrons are present in the centre of an atom which is called nucleus whereas electrons are present some distance away from the nucleus in different shells. Some particles of electron, proton and neutron are given below:

 

Particle	Relative mass	Relative charge
Electron	1/1840 (negligible)	-1 (Negative)
Proton	1	+ 1 (Positive)
Neutron	1	O (Neutral)

                       

            Atom has a whole is electrically neutral, since its contains same number of electrons and protons. The size of nucleus is very small as compared tp the size of atom.

 

BEHAVIOUR OF PROTONS, NEUTRONS AND ELECTRONS IN ELECTRIC FIELDS:

n

+

-

 

In the electric fields sub-atomic particles are deflected according to their relative charges. Electrons being negative are deflected toward positive ole whereas protons are deflected toward negative pole because protons are positively charged and neutrons remain un-deflected because they are neutral particles. It is also observed that beam of electrons is deflected mole than beam of protons because electrons are lighter particles than protons. Hence, they are deflected earlier and more in electric field.

 

           

DISTRIBUTION OF MASS AND CHARGES WITHIN AN ATOM:

 

            The mass of a proton and neutron is almost same whereas electrons are lighter particles. The mass of an electron is about 1840 times lesser than that of a proton or a neutron. Both protons and neutrons are present in the centre of an atom which is called nucleus of an atom. Thus nucleus is positively charged. Electrons are present out-side the nucleus ate some distance in different shells. Electrons are negatively charged thus positively charged nucleus is surrounded by cloud of negative charge. Atom as a whole is electrically neutral since, it contains same number of protons and electrons Mass of an atom is due to protons and neutrons since mass of electrons is negligible. Thus since of protons and neutrons in and atom is called nucleus number or mass number of an atom. It is represented by A . Overall, whole mass and positive charge is concentrated in the nucleus and its surrounded by negatively charged electrons cloud. e.g;

 

            Nucleus of sodium have 11 protons and 12 neutrons, since its mass number is 23 similarly it has 11 electrons because number of electrons must be equal to number of protons.

DEDUCTION OF NUMBERS OF PROTONS, NEUTRONS AND ELECTRONS IN THE ATOMS AND IONS FROM THE GIVEN PROTONS AMD NUCLEUS NUMBERS (AND CHARGE):-

 

            Number of protons in the nucleus of an atom or ion is called charge no or atomic number. It is represented by symbol. Whereas nucleus number  is the since of protons and neutrons present in the nucleus. It is represented by symbol A. Hence No of neutron = (A-Ƶ)

            Since atom as a whole is electrically neutral, thus no of electrons are equal to no of protons.  On the other side ions are formed due to given or lose of electrons. As negative ions are formed due to gain of electrons thus they have more no of electrons than protons. Similarly positive ions are formed due to lose of electrons, hence they have less number of electrons than protons e.g.

 

            Sodium atom, ²³Na P=11, E=11, N= (A-Z) 

= 23-11

N = 12

            Whereas sodium ion ²³Na^H 

                                                P = 11, E = 10, N = 12

            In case of nitrogen atom;

                                                N

                                               

                                                P = 7, E = 7, N = (A-Z)

                                                                     N + (14-7)

            Whereas in nitrogen ions;

                                                N3-

                                               

                                                P = 7, E = 10, N = 7