5.1 Models of the Atom Models of the atom began with Dalton and have changed over time. As our knowledge of the atom changes so does our model of the atom.

5.1 Models of the Atom Each new model shows our greater understanding of the atom’s structure.

Think back to Rutherford’s Gold foil experiment. What did Rutherford say about the atom? –Atoms mostly empty space –Nucleus dense and positive –Electrons orbit the nucleus like planets orbit the sun Rutherford’s model did not explain chemical properties of elements –His model also did not explain why objects change color when heated 5.1 Models of the Atom What was wrong with Rutherford’s Model?

-Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus. -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 Models of the Atom Bohr’s Model Bohr Model

5.1 Models of the Atom Bohr’s 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.

5.1 Models of the Atom Current atomic model: Quantum Mechanical Model Still has the nucleus containing protons and neutrons in the center. Still has electrons outside the nucleus in a low density area 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. This model is based on equations developed by Erwin Schrodinger

5.1 Models of the Atom Current atomic model: 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 Models of the Atom Current atomic model: 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 Models of the Atom Principal Energy Levels of Electrons: Principal Energy levels and # of electrons in each: Level 1 Holds 2 Level 2 Holds 8 Level 3 Holds 18 Level 4 Holds 32

5.1 Models of the Atom Principle energy levels are broken down into sublevels called: 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. Each orbital contains up to 2 electrons Orbitals include: s, p, d, and f

Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped. The s sublevel contains 1 orbital, so up to 2 electrons The p sublevel contains 3 orbitals, so up to 6 electrons 5.1 Models of the Atom Atomic Orbitals

Four of the five d orbitals have the same shape but different orientations in space. Since there are 5 orbitals, up to 10 electrons can be found in the d sublevel. 5.1 Models of the Atom Atomic Orbitals

F orbitals. There are 7 with complex shapes. A few are shown below: Since there are 7 orbitals, up to 14 electrons can be found in the f orbitals. 5.1 Models of the Atom Atomic Orbitals

Sublevel # of Orbitals # electrons in sublevel Shape s12Sphere p36Dumbbell d510Double Dumbbell f714Complex shapes Principle Energy Level # of Sublevels Identity of Sublevels # of orbitals Max. # of electrons 11s12 22s, p1 + 3 = 48 33s, p, d1+3+5 = s, p, d, f = Models of the Atom Atomic Orbitals Summary of Sublevels & Orbitals