5: Electrons in Atoms
- Page ID
- 52952
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- 5.4: Photoelectric Effect
- The photoelectric effect is a phenomenon that occurs when light shined onto a metal surface causes the ejection of electrons from that metal. It was observed that only certain frequencies of light are able to cause the ejection of electrons. If the frequency of the incident light is too low (red light, for example), then no electrons were ejected even if the intensity of the light was very high or it was shone onto the surface for a long time.
- 5.9: Quantum Mechanics
- Quantum mechanics is the study of the motion of objects that are atomic or subatomic in size and thus demonstrate wave-particle duality. In classical mechanics, the size and mass of the objects involved effectively obscures any quantum effects so that such objects appear to gain or lose energies in any amounts. Particles whose motion is described by quantum mechanics gain or lose energy in the small pieces called quanta.
- 5.10: Heisenberg Uncertainty Principle
- The Heisenberg Uncertainty Principle explains why we cannot simultaneously determine both the precise velocity and position of a particle. This principle is only applicable at the atomic level.
- 5.11: Quantum Mechanical Atomic Model
- The quantum mechanical model of the atom comes from the solution to Schrödinger's equation. Quantization of electron energies is a requirement in order to solve the equation. Solutions to the Schrödinger wave equation, called wave functions, give only the probability of finding an electron at a given point around the nucleus. Electrons do not travel around the nucleus in simple circular orbits.
- 5.13: Orbitals
- We can apply our knowledge of quantum numbers to describe the arrangement of electrons for a given atom. We do this with something called electron configurations. They are effectively a map of the electrons for a given atom. We look at the four quantum numbers for a given electron and then assign that electron to a specific orbital in the next Module.
- 5.14: Quantum Numbers
- We use a series of specific numbers, called quantum numbers, to describe the location of an electron in an associated atom. Quantum numbers specify the properties of the atomic orbitals and the electrons in those orbitals. An electron in an atom or ion has four quantum numbers to describe its state. Think of them as important variables in an equation which describes the three-dimensional position of electrons in a given atom.
- 5.15: Aufbau Principle
- to create ground state electron configurations for any element, it is necessary to know the way in which the atomic sublevels are organized in order of increasing energy. The Aufbau principle states that an electron occupies orbitals in order from lowest energy to highest. The Aufbau (German: "building up, construction") principle is sometimes referred to as the "building up" principle.
- 5.16: Pauli Exclusion Principle
- The Pauli exclusion principle, which states that no two electrons in an atom can have the same set of four quantum numbers. The energy of the electron is specified by the principal, angular momentum, and magnetic quantum numbers. If those three numbers are identical for two electrons, the spin numbers must be different in order for the two electrons to be differentiated from one another.
- 5.17: Hund's Rule and Orbital Filling Diagrams
- Hund's rule states that orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron and that each of the single electrons must have the same spin. An orbital filling diagram is the more visual way to represent the arrangement of all the electrons in a particular atom. In an orbital filling diagram, the individual orbitals are shown as circles (or squares) and orbitals within a sublevel are drawn next to each other horizontally.
- 5.18: Electron Configurations
- Electron configuration notation eliminates the boxes and arrows of orbital filling diagrams. Each occupied sublevel designation is written followed by a superscript that is the number of electrons in that sublevel.
- 5.19: Valence Electrons
- Valence electrons are the electrons in the highest occupied principal energy level of an atom. In the second period elements, the two electrons in the 1s sublevel are called inner-shell electrons and are not involved directly in the element's reactivity or in the formation of compounds.
- 5.20: Noble Gas Configuration
- A noble gas configuration of an atom consists of the elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons.