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Explain the Bohr's model?
Bohr's Model : Electrons move around the nucleus at tremendous speeds and occupy most of the space in an atom. The exact position or location of an electron at any given moment can only be predicted on the basis of probability. In a widely accepted model of the atom originally proposed by Neils Bohr, electrons move in spherical spaces called orbitals, or shells, which correspond to different energy levels. Electrons are distributed according to their energy levels, with the higher energy electrons residing in the outer shells. The innermost shell contains only 2 electrons. In common elements, the next outer shells contain 8 electrons each.
Atoms either gain, lose, or share electrons in the outer shells. Because the outer shells of many atoms are incomplete, most atoms will interact with other atoms during chemical reactions to achieve stable outer shells. The number of electrons that an atom must either gain, lose, or share to complete the outer shell is known as its valence, or oxidation number. For example, carbon has six electrons, two in its first energy level and four in the outer level. Thus, it can form a stable outer shell by gaining, losing, or sharing four electrons to complete its outer shell when it joins, or bonds, with another atom or atoms to form a compound. The following table lists the oxidation numbers of some important ions frequently used in Biology.
Depleted (Vulnerable) Species These are the species whose numbers are greatly reduced from those of the recent past, and they are continuing to decrease. It is the continued d
TRISACCHARIDES The oligosaccharides are made of three monosaccharide residues. A common trisaccharides is Raffinose which is formed by condensation of galactose-glucose-fr
• Cancer cells do not respond normally to the body's control mechanism. o They divide excessively and invade other tissues. o If left unchecked, they can kill the organism. •
Indications for Surgery: In a mixed lesion, either regurgitation or stenosis may be dominant and decision of surgery depends on the haemodynarnics. At the time of surgery on othe
Louis Pasteur (1860-1862) French): Even after the experiments of Spallanzani, the conflict of a biogenesis and biogenesis continued well into the middle of 19 th century till
Explain why the chance of fertilisation in humans is restricted to only a few days each month. Sperms can fertilise an ovum for up to about three days after entering the female
How are genetic diseases classified? The Genetic diseases classify into chromosomal abnormalities and genetic mutations. Between chromosomal abnormalities there are the aneu
Select the two correct statements out of the four (a - d) given below about lac operon. 1. Glucose or galactose may bind with the repressor and inactivate it 2. In the absenc
Why is rubella during gestation a threat to the fetus? If occurring during gestation rubella is a dangerous disease due to the virus crosses the placenta and contaminates the f
DISORDERS OF LIVER: In the foregoing sections and sub-sections we have discussed about the common disorders of upper and lower gastrointestinal tract. Now we shall discuss
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