GENERAL CHEMISTRY

GENERAL CHEMISTRY

Is a branch of chemistry which deals with behaviour and characteristics of electrons.

This subtopic deals with electron occupying space in an atom. The electron occurs in the orbit/ shell at the region called orbital. The orbital is the region where there is a maximum probability of locating electron. At the same time this topic deals with electron of atom which occurs in a chemical compound. The general chemistry includes the following aspects or subtopics:-

·   Atomic structure.

·   Atomic spectrum/ H – spectrum.

· Wave mechanics.

·  Chemical bonding.

1.0 ATOMIC STRUCTURE

Atomic structure deals with structure and component of an atom. The first scientist discovered that matter is made up of small particles called atoms. The term atom means indivisible particles. But later, different scientists put forward atomic models. These atomic models account for atomic structure. There are several atomic models which include the following:-

 • Dalton’s atomic theory.
 • Thompson’s atomic theory.
• Bohr’s atomic model.
• Rutherford atomic model.
• Wave particles duality nature of matter. 
• Heisenberg uncertainity principle.

DALTON’S ATOMIC THEORY

Dalton’s atomic theory includes the following main points:-

i. Matter is made up of small indivisible particles called atoms.

ii. Atom is neither created nor destroyed.

iii.Atoms of the same elements are similar especially in mass.

iv. Atoms of different elements are different especially in mass.

v. Atoms of different elements when combine they do so in small ratio whole numbers.

RECENT MODIFICATION OF DALTON’S ATOMIC THEORY

Dalton’s atomic theory was modified because all points were not valid. This resulted into discover of modern atomic theory. The following include point of modern atomic theory:-

i.  Matter is made up of small indivisible particles called atoms was not valid due to the existence of three particles in atom. Matter is made up of a small divisible particle called atoms.

Particle	Nature of change	symbol	mass	Position
Proton	+1	11P	1.00	Nucleus
Neutron	0	01n	1.00	Nucleus
Electron	-1	-10e	1/1840	Shell

ii.   Atom is neither created nor destroyed was not valid due to the existence of radioactivity therefore Atom can be created or destroyed by either nuclear fission or fusion.

iii.  Atoms of the same elements are similar especially in mass was not valid due to the existence of isotopes. Atoms of the same elements have either same or different mass.

iv.  Atoms of elements are different especially in mass was not valid. Atoms of different elements have either same or different mass.

v.  Atoms of different elements when combine they do so in small ratio of whole number was not valid because different elements combine by using variable ratio of whole number.

THOMPSON's EXPERIMENT (DISCOVERY OF ELECTRONS)

Thompson’s conducted an experiment to investigate if air conducts electricity. The following circuit was used during the experiment.

• The emission tube have electrode at each end which is connected to the external circuit. The emission tube is connected to the vacuum pump in order to maintain the low pressure in         the emission tube.      
    
The circuit is switched  on which results into the following observation:-
   
• The bulb emitted light which indicate that the gas conduct electricity.
   
• There is glowing of emission tube or emission of light.
 
• There is fluorescence of emission tube.
 
• The stream of rays running from cathode to the anode. Through investigation of properties of cathode rays by using magnetic field, electric field and gold electroscope results into discover of electron. The cathode rays were the electrons.

EXPLANATION OF THOMPSON’S EXPERIMENT IN TERMS OF ATOMIC STRUCTURE

Ground state: Is lowest energetic state of an atom. Is a state when an electron filled in the lowest energy level before filling the highest energy level available. The electron filled in atom in order of increasing energy level. This state make atom to be stable.

Excited state: Is a state of an atom when electron filled in the highest energy level before filling lowest energy level available. If the electron excited jumps to the extent that the nuclear attractive force act upon it result pulling back of electrons. When return back to the ground state release all amount of energy which was absorbed inform of radiation.

RADIATION: This energy causes glowing of emission tube. When the radiation strikes the emission tube causes florescence of emission tube.

Convergent limit: Is a state of atom when an electron is removed completely from ground state to the infinite. The convergent limit occurs if atom gain high energy which result electrons to jump to the highest energy level where the nuclear attractive force cannot act up on it. This electron cannot return back to the ground state it result the atom left to positively charged. The convergent limit is a factor which causes some electrons to move from cathode to anode. These were stream of rays called cathode rays which later was electrons.

SIGNIFICANCE OF CONVERGENT LIMIT

These include the following:-

• It resulted into discover of the ionization energy. This ionization energy used in the inorganic section.     

• It resulted into formation of ion particles. The ionic particle is more reactive when take part during chemical reaction.

• It resulted into production of rays. These rays are known as atomic spectrum.

THOMSON MODEL OF THE ATOM

After the discovery of electrons and protons, the next question was to know how these particles are arranged in an atom. The first simple model of the atom was proposed by J.J.Thomson in 1898.The Thomson atomic model is popularly known as the Thomson's "plum-pudding" model of the atom.

Thomson considered an atom to be a sphere (radius = 10^-10 m or 10^-8 cm) of uniform positive charge into which the negatively charged electrons were embedded. This model is like plum-pudding dotted with raisins

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