Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

N-shell (n=4) 8.2.3 Bohr’s model of the atom M-shell (n=3) To explain why atoms are stable, Niels Bohr L-shell (n=2) proposed a new model of the atom in 1913. K-shell (n=1) According to Bohr: Nucleus y Electrons do not move randomly around the nucleus but follow fixed circular paths called stationary states, orbits, or shells. In each shell, an electron has a definite amount of energy, so these shells are also called energy levels. Fig. 8.7: Energy levels in an y These shells are represented by the letters K, L, atom M, N, ... or by the numbers n = 1, 2, 3, 4, ... (Fig. 8.7). y Electrons can revolve only in these allowed shells, and not in between them. While moving in a fixed shell, an electron does not lose energy. Meet a Scientist y The first energy level K (n = 1) is the one closest to the nucleus (Fig. 8.7) and has the least energy. y The energy of these levels increases as we move away from the nucleus. That is, the energy of an electron in the L-shell (n = 2) is more than that of an electron in the K-shell (n = 1). The farther away a shell is from the nucleus, the higher is its energy. An electron can move to another shell by absorbing or releasing a y fixed amount of energy equal to the difference between the energies of the two levels. Niels Bohr was Each shell can hold only a certain number of electrons. a professor y of physics at You may be wondering, how does Bohr’s model explain stability? Copenhagen In Bohr’s model, electrons also move in circular paths around the University, positively charged nucleus, as in Rutherford’s model. But why don’t Denmark. He they lose energy while doing so? Bohr addressed this by introducing the was curious about how atoms concept of stationary states as a postulate. In a stationary state, the energy of an electron remains constant, even though it is in motion around the exist because nucleus. Bohr’s model could explain many experimental observations the old models and marked a major step in understanding the atomic structure. could not explain why electrons stay around the Threads of Curiosity nucleus without collapsing. His Why are Bohr’s shells called K, L, M, N... and not, A, B, C, D? explanation of the atomic structure The naming came from early X‑ray experiments by the physicist, Charles provided more Barkla, who called the first observed X-ray line K. He didn’t start naming from A to leave room for possible discovery of a series earlier than the clarity. Niels Bohr K series, although none were ever found. Bohr adopted the same notation received the Nobel for atomic shells. Prize in 1922, for his work on the structure of the Later, even Bohr’s model was found to have limitations, and yet atom. Next another model, the quantum mechanical model, was proposed. LUpel You will learn about it in higher grades. 146 Exploration|Grade 9