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Understand atomic structure in physics

           ATOMIC STRUCTURE

 ATOM: Is the smallest particle of an element that can take part in a chemical reaction.

Atoms as the smallest particles have ability to exist on its own. Dalton was the first person to use the word ATOM.

DALTON ATOMIC THEORY

1. All matter are made up of tiny particles called ATOM.
2. Atoms can neither be created nor destroyed.
3. Atoms of a given element are identical. They have the same atomic mass and similar chemical properties.
4. Atoms of one elements can combine with atoms of other elements to form molecules.
5. Atoms of given element are different from those of other elements.

MODIFICATION OF DALTON ATOMIC THEORY

1. Atoms are made up of smaller particles called electrons, protons and neutrons.

2. Atom can be created or destroyed or split up by nuclear reaction/ nuclear fission.

3. Some element have atom of more than one type. They are called Isotopes.

4. Atoms of different elements combine together to form complex compound.

SUB ATOMIC PARTICLES

• Atom are made up of 3 particles these are;

- PROTON

- ELECTRON

- NEUTRON

• All atoms of an element have both 3 particles except hydrogen which has no Neutron.

A:   THE ELECTRON

• This is a negatively charged particle (-ve)
• It's mass is about;

                                 

• It's  symbol is 'e'
• It rotates around the nucleus in a particular patten called shell or energy level

B:   THE PROTON

• This is a positively charged particles (+ve)

• It has mass approximately the same as that of hydrogen atom ie atomic mass
• It is symbol is (p) or +₁¹P
• It is found in the nucleus of an atom

C:   THE NEUTRON

• This is a neutral  particle or is a particle which has .no charge
• The mass is the same as that of protons ie atomic mass unit
• It symbol is (n)

•  It is found in the nucleus of an atom
• summary

              

• ATOMIC STRUCTURE

           

Although an atom contain charge particles (protons) and electron is natural because the number of protons (+Ve) are equal to the number of electron (-Ve)

THE ARRANGEMENT OF ELECTRONS IN ATOM

ELECTRONIC CONFIGURATIONS

Electronic configuration: Is the distribution of electrons in various shell of an atom.
     The maximum number of electrons held within each energy level. It  can be determined by the formula 2n^{2
       Where n is the position of energy level from the nucleus}

• The first shell from the nucleus of an atom have ability of carrying only 2 electron. ⇒(2×1² ) = 2 electrons
• The second shell from the nucleus of an atom has ability of carrying only 8 electrons. ⇒( 2×2²) = 8 electrons
• The third shell from the nucleus of an atom have ability of carrying only 8 electronic. ⇒ (2×3²) =18 electrons
• The forth shell from the nucleus carry a maximum of 18 electrons. ⇒ (2×4²) = 32 electrons

NOTE; But the third energy level is stable with 8 electrons

   

Example of electron diagrams of an atom;
  
           1. Hydrogen, 1=1

                   
          
           2. Aluminium, 13=2:8:3

                      
   

           3. Chlorine, 17 =2:8:7
       
                     

           4. Oxygen, 8= 2:6

                    

ELECTRONS CONFIGURATIONS OF FIRST ELEMENT

Element	Symbol	Number of neutron	Atomic number/Proton and Electron	Atomic Mass	Electronic configuration (KLMN)	Number of shell
Hydrogen	H	0	1	1	1	1
Helium	He	2	2	4	2	1
Lithium	Li	4	3	7	2:1	2
Beryllium	Be	5	4	9	2:2	2
Boron	B	6	5	11	2:3	2
Carbon	C	6	6	12	2:4	2
Nitrogen	N	7	7	14	2:5	2
Oxygen	O	8	8	16	2:6	2
Florine	F	10	9	19	2:7	2
Neon	Ne	10	10	20	2:8	2
Sodium	Na	12	11	23	2:8:1	3
Magnesium	Mg	12	12	24	2:8:2	3
Aluminum	Al	14	13	27	2:8:3	3
Silicon	Si	14	14	28	2:8:4	3
Phosphorus	P	16	15	31	2:8:5	3
Sulphur	S	16	16	32	2:8:6	3
Chlorine	Cl	18	17	35	2:8:7	3
Argon	Ar	18	18	36	2:8:8	3
Potassium	K	19	19	38	2:8:8:1	4
Calcium	Ca	20	20	40	2:8:8:2	4

NOTE

1.  In the above the element are arranged according to the increase in atomic number
2. The number of proton = number of electron = Atomic number
3. The mass number (A) is the sum of proton  (P) and neutron (N): (A = P+N)

ATOMIC NUMBER, MASS NUMBER AND ISOTOPES
ATOMIC NUMBER (Z)
   Is the number of proton in the nucleus of an atom which is equal to the number of electron in the shell.

• It's official symbol is (Z).
• Atomic number is written on left hand side below the symbol of an element.

• Therefore atomic number of the following element are written as ₆C , ₈O  _{, 17}Cl , ₂₀Ca
• Also atomic number = number of proton = number of electron

 
      2. MASS NUMBER / ATOMIC MASS (A)

• It is written on left hand side above the symbol of an element.

E.g;

              

.E.g. Carbon atomic mass is 12 written as ¹²C chlorine atomic mass is written as ³⁵Cl

• The official symbol for mass number is A.
• Combination of mass and atomic number are;

                                                                          

Therefore Atomic mass = Proton (atomic number)
Example; Atom R has mass number of 40 and an atomic number of 20. What is it’s neutron number , and what is the number of electrons in an atom R ?
           

Solution ; mass number = 40
             atomic number = 20

      (a) Neutron number = mass number − atomic number
  
                                 =    40    −    20
        ∴ Neutron number =    20

      (b) Number of electrons = number of protons =  atomic number = 20  
                   

ISOTOPES

      These are atoms of the same element which have the same atomic number but they differ in mass number.

• Isotopes have the same proton electron and atomic number.
• They have same chemical properties but have slight different physical properties.
• Isotopes has different mass number because they have different number of neutrons.
• Example of element which have the isotopes;

                                         

NOTE:

• in the above four examples, the numbers above  the  element in the isotopes are the mass numbers.
• The numbers below  the element are atomic numbers.
• From the definition of the isotopes, it is true that mass number are different and atomic number are the same.

RELATIVE ATOMIC MASS (RAM)

• The relative atomic mass of an element is the mass of an atom of carbon twelve(12) Isotopes .

         

• If an element has several Isotopes its relative atomic mass will be the mass of Isotopes on calculation. The average mass of the proportion (abundance) of each Isotope in the sample of element must be known.
• This is calculated by working out the relative abundance of each isotope

                                                  CALCULATING RELATIVE ATOMIC NUMBER

Relative atomic mass (RAM) =( Relative abundance × Atomic mass ) + ( Relative abundance × Atomic mass )
                                                                                      100

Example:  

1. A sample of chlorine gas contains 75%  and 25% of the Isotopes with it’s relative abundance of 35 and 25 respectively. What is the relative atomic mass (R.A.M) of chlorine?

RAM =( Relative abundance × Atomic mass ) + ( Relative abundance × Atomic mass)
                                                                                      100

                                                                                      

To get the answer multiply the mass number of each Isotopes with the abundance.

Solution

R.A.M of chlorine     =   35.5

• The relative atomic mass of chlorine is 35. 5. The word symbol of relative atomic mass is (RAM).

2. A sample of chlorine is a mixture of two Isotopes in the ratio of 3:1. What is the relative atomic mass of chlorine atom?

Solution

R.A.M of chlorine     =   35.5

 
3. A sample of Oxygen is mixture of 3 Isotopes in the ratio of 3:2:1. What is relative atomic mass (R.A.M).

Solution

R.A.M   of Oxygen     =   16.6

                                      REVIEW QUESTION

               1.  Define the following

                                       (i) Atomic

                                       (ii) Electronic configuration

                                       (iii) Atomic number

                                       (iv) Mass number

                                       (V) Isotope
 

            
           
        3. Copy and complete the following table of atomic / electron structure of same element
  
             (a).
                        

          

               

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