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5.1 Models of the Atom • The scale model shown is a physical model. However, not all models are physical. In fact, several theoretical models of the atom have been developed over the last few hundred years. You will learn about the currently accepted model of how electrons behave in atoms.
5.1 The Development of Atomic Models • The Development of Atomic Models • What was inadequate about Rutherford’s atomic model?
5.1 The Development of Atomic Models • Rutherford’s atomic model could not explain the chemical properties of elements. • Rutherford’s atomic model could not explain why objects change color when heated.
Rutherford’s atom • The nucleus of the atoms contained the protons and neutrons. The electrons surrounded the nucleus. • First planetary model of the atoms
5.1 The Development of Atomic Models • The timeline shows the development of atomic models from 1803 to 1911.
5.1 The Development of Atomic Models • The timeline shows the development of atomic models from 1913 to 1932.
5.1 The Bohr Model • The Bohr Model • What was the new proposal in the Bohr model of the atom? • Bohr felt changes were needed for the Rutherford atom. Explaining how the atom changes as it absorbs and emits light.
5.1 The Bohr Model • Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
5.1 The Bohr Model • Each possible electron orbit in Bohr’s model has a fixed energy. • The fixed energies an electron can have are called energy levels. • A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.
5.1 The Bohr Model • Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced. • The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.
Bohr use his atomic model to relate the hydrogen atom’s energy states to the motion of the electrons with in the atom. • A single electron in a hydrogen atoms moves around the nucleus in only certain allowed circular orbits. The smaller the orbit , the lower the orbits energy. • He assigned n= principal energy level. • Lowest energy level is called its ground state.
Bohr continued • The Bohr model agreed with the hydrogen atom • But failed to explain the energies absorbed and emitted by atoms with more than one electron.
5.1 The Quantum Mechanical Model • The Quantum Mechanical Model • What does the quantum mechanical model determine about the electrons in an atom?
5.1 The Quantum Mechanical Model • The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.
5.1 The Quantum Mechanical Model • Austrian physicist Erwin Schrödinger (1887–1961) used new theoretical calculations and results to devise and solve a mathematical equation describing the behavior of the electron in a hydrogen atom. • The modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrödinger equation.
5.1 The Quantum Mechanical Model • The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.
5.1 The Quantum Mechanical Model • In the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high.
5.1 Atomic Orbitals • Atomic Orbitals • How do sublevels of principal energy levels differ?
5.1 Atomic Orbitals • An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron. • Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.
5.1 Atomic Orbitals • Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped.
5.1 Atomic Orbitals • Four of the five d orbitals have the same shape but different orientations in space.
F orbitals have 7 different orientations • Maxinum number of electrons 14 electrons that could be place in these orbital. F orbitals begin to fill in the 4 th energy level.
The number of the principal energy level = the number of the sublevels • 1 energy level only has one sublevel s. • 2 nd energy level has 2 sublevels: s and p • 3rd energy level has ? sublevels
Questions • What do the subscripts such as y and xz tell you about atomic orbitals? • ans: orientations
Questions • What is the probability that an electron will be found within an atomic orbital? • Ans 90%
5.1 Atomic Orbitals • The numbers and kinds of atomic orbitals depend on the energy sublevel.
5.1 Atomic Orbitals • The number of electrons allowed in each of the first four energy levels are shown here. • Formula to calculate the total total number of • electrons in an energy • level 2n2 n = principal • energy level
How many electrons are in the 6 th energy level? • 2 n2 • 2 (6)2= 72 e
5.1 Section Quiz. • 1. Rutherford's planetary model of the atom could not explain • any properties of elements. • the chemical properties of elements. • the distribution of mass in an atom. • the distribution of positive and negative charges in an atom.
5.1 Section Quiz. • 2. Bohr's model of the atom proposed that electrons are found • embedded in a sphere of positive charge. • in fixed positions surrounding the nucleus. • in circular orbits at fixed distances from the nucleus. • orbiting the nucleus in a single fixed circular path.
5.1 Section Quiz. • 3. What is the lowest-numbered principal energy level in which p orbitals are found? • 1 • 2 • 3 • 4
