Electrons In Atoms Chapter 5

Atomic Models Plum Pudding Model Nuclear Model Developed by JJ Thomson Atom is made of positive material with electrons sitting in this positive material Nuclear Model Developed by Ernest Rutherford Atom has a positive nucleus with electrons moving around it --- rest of the atom is empty space Could not explain why metals or compounds of metals give off characteristic colors when heated in a flame Could not explain the chemical properties of elements

Bohr Model Developed by Niels Bohr Considered the simplest atom (hydrogen)—has one electron Electron is found only in specific circular paths, or orbits, around the nucleus Each electron orbit has a fixed energy These fixed energies are called energy levels An electron can jump from one energy level to another Must gain or lose the right amount of energy Amount of energy required to move an electron from one energy level to another energy level is known as a quantum of energy Electrons cannot be between energy levels The higher an electron is on the energy level, the farther it is from the nucleus

The energy levels are not equally spaced Higher energy levels are closer together The higher the energy level the less energy it takes to move from that energy level to another energy level Problem with Bohr Model: It failed in many ways to explain the energies absorbed and emitted by atoms with more than one electron

Quantum Mechanical Model Developed by Erwin Schrödinger Modern description of electrons in atoms that comes from the mathematical solutions to the Schrödinger equation restricts the energy of the electrons, but the electrons do not have an exact path around the nucleus Determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus The probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud Cloud is more dense in areas where the probability of finding the electron is high

Atomic Orbitals A region of space in which there is a high probability of finding an electron Electrons can exist in several discrete principal energy levels Each is designated by the principal quantum number(n) that are integers (1, 2, 3, 4, etc) Each principal energy level consists of energy sublevels that have slightly different energy values Designated by the letters s, p, d, and f The principal quantum number will tell you the number of sublevels in that particular energy level Ex: n=1 1st energy level has 1 sublevel

All orbitals in the same sublevel have equal energy Each sublevel contains one or more orbitals, each of which can hold two electrons s sublevel has one orbital p sublevel has 3 orbitals d sublevel has 5 orbitals f sublevel has 7 orbitals All orbitals in the same sublevel have equal energy Each orbital also has a specific shape s orbital is spherical

p orbitals have this shape d orbitals have this shape

f orbitals have this shape

To determine how many orbitals each energy level contains use the equation n2 Remember: n = energy level To determine how many electrons each energy level will hold use the equation 2n2