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The Atom Objectives Previous Unit To know the three elementary particles which compose atoms. To understand the development of the atomic model. Let’s take this one step further… Objectives Unit 4 Objective 1 - To understand the Quantum Mechanical Model of the atom as it applies to principle energy levels and sublevels. Objective 2 – Be able to apply the Aufbau Principle, the Pauli Exclusion Principle, and Hund’s Rule in writing electron configurations of elements, and understand why there are some exceptions. Objective 3 – Be able to calculate wavelength, frequency, and energy of light and understand the origin of the atomic emission spectrum of an element. Objective 4 – Describe the different groups on the periodic table and relate them to their electron configurations. Objective 5 – Interpret group and periodic trends in atomic radii, ionic radii, ionization energies, and electronegativities. The Atom Today Over time, the model of the atom evolved. Two early models we saw were: Thomson’s Plum Pudding Model Rutherford’s Nuclear Atom The Atom Today The model proposed by Niel’s Bohr was the Planetary Model The central nucleus (like the sun) surrounded by orbiting electrons (like the planets) Explained that electrons don’t fall into nucleus because they have fixed energy The Bohr model was an improvement, but was replaced by the… Quantum Mechanical Model Modern model of the atom No longer are electrons treated like they travel like “classical” particles (bowling balls) Focus is on electrons Electrons are found not in orbits but in “clouds” Based on probabilities Area where there is a 90% chance of finding an electron Electron clouds Are 3-dimensional Come in several shapes Are tied to specific energies Energy levels fill in special order Organizing Electrons Electrons in an atom are organized into different energy levels 1. Principal energy levels have sublevels 2. Sublevels take the form of atomic orbitals 3. Orbitals “contain” electrons Principal Energy Levels (n) Principal energy levels (n) are numbered Maximum number of electrons in a level is 2n2 n = 1 n = 2 n = 3 2 x 12 = 2 electrons 2 x 22 = 8 electrons Each principal level has a number of sublevels equal to the level number n = 1 n = 2 1 sublevel 2 sublevels Sublevels Each sublevel contains a certain number of atomic orbitals Orbitals are regions where it is likely an electron will be found Each orbital can hold a maximum of 2 electrons Letters are used to denote orbitals Orbitals have characteristic shapes Atomic Orbitals Orbital How many per Shape sublevel? s 1 spherical p 3 peanut d 5 4 are double-peanut 1 is a donut-ringed peanut f 7 flower Orbitals are regions in Space The energy level of an electron is the region around the nucleus where the electron is likely to be moving. S orbital is a sphere P orbitals Each P orbital can hold two electrons, but they need to have opposite spins The P sublevel holds 6 electrons D level orbitals Each The D sublevel can hold 10 electrons. Each orbital holds 2 electrons with opposite spins The F sublevel has 7 orbitals Each orbital can hold 2 electrons with opposite spin The F sublevel holds 14 electrons The F Sublevel Atomic Orbitals s p d f Electrons can change orbitals Electrons can change orbital, by absorbing energy. When an electron absorbs a quantum of energy, it moves up to a higher orbital. When the electron falls from a high orbital to a lower orbital, energy is released, and we see light. Wintergreen mint is an example We will also see this in our spectroscopy and flame test labs! Atomic Orbitals Electron configurations A series of numbers and letters to show which orbitals contain electrons for a given element Before we proceed… Aufbau Principle Electrons enter orbitals of the lowest energy first Pauli Exclusion Principle No two electrons can have the same “state” • State = electron’s orbital and its spin • Electrons in the same orbital will have opposite spin Hund’s Rule When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with spin in the same direction