Ch. 5.1 Models of the Atom

The Development of Atomic Models Rutherford’s model, with the protons and neutrons in a nucleus surrounded by electrons, couldn’t explain the chemical properties of elements. Rutherford’s model, with the protons and neutrons in a nucleus surrounded by electrons, couldn’t explain the chemical properties of elements. Niels Bohr proposed that an electron is found only in specific circular paths around the nucleus, in fixed, exact energy levels. Niels Bohr proposed that an electron is found only in specific circular paths around the nucleus, in fixed, exact energy levels. Electrons must gain or lose exact amounts of energy (quantums) to change energy levels. Electrons must gain or lose exact amounts of energy (quantums) to change energy levels.

An analogy of Bohr’s energy levels would be the rungs on a ladder, except the rungs would not be evenly spaced. The higher rungs (energy levels) would be closer together. An analogy of Bohr’s energy levels would be the rungs on a ladder, except the rungs would not be evenly spaced. The higher rungs (energy levels) would be closer together.

The Quantum Mechanical Model Experimental results were inconsistent with the idea of electrons moving like large objects in orbit. Experimental results were inconsistent with the idea of electrons moving like large objects in orbit. Schrodinger proposed the quantum mechanical model. It does not involve the exact path an electron takes around the nucleus. Schrodinger proposed the quantum mechanical model. It does not involve the exact path an electron takes around the nucleus.

The model determines the allowed energy an electron can have, and how likely it is to find the electron in various locations around the nucleus. The model determines the allowed energy an electron can have, and how likely it is to find the electron in various locations around the nucleus.

Atomic Orbitals Schroeinger’s equation gives the energy levels an electron can have, but also describes the probability of finding an electron at various locations around the nucleus, called atomic orbitals. Schroeinger’s equation gives the energy levels an electron can have, but also describes the probability of finding an electron at various locations around the nucleus, called atomic orbitals. Energy levels are labeled by principal quantum numbers (n). n = 1, 2, 3, etc. Energy levels are labeled by principal quantum numbers (n). n = 1, 2, 3, etc. Several orbitals with different shapes and energy levels (sublevels) exist within each principal energy level. Several orbitals with different shapes and energy levels (sublevels) exist within each principal energy level.

Each energy sublevel corresponds to an orbital of different shape describing where the electron is likely to be found. Each energy sublevel corresponds to an orbital of different shape describing where the electron is likely to be found. Different atomic orbitals are denoted by letters…s, p, d, f. Different atomic orbitals are denoted by letters…s, p, d, f. s orbitals are spherical; p orbitals are dumbbell-shaped. The three kinds of p orbitals have different orientations in space. s orbitals are spherical; p orbitals are dumbbell-shaped. The three kinds of p orbitals have different orientations in space.

Other orbitals have different and more complex shapes. Other orbitals have different and more complex shapes. When n = 1, it has one sublevel…1s. When n = 1, it has one sublevel…1s. n = 2 has two sublevels…2s and 2p. n = 2 has two sublevels…2s and 2p. n = 3 has three sublevels…3s, 3p, and 3d. n = 3 has three sublevels…3s, 3p, and 3d. n = 4 has four sublevels…4s, 4p, 4d, 4f. n = 4 has four sublevels…4s, 4p, 4d, 4f. The principal quantum number always equals the number of sublevels within that principal energy level. The principal quantum number always equals the number of sublevels within that principal energy level.

The maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2. The maximum number of electrons that can occupy a principal energy level is given by the formula 2n 2.