The Atom

Objectives Previous Unit Let’s take this one step further… To know the three elementary particles which compose atoms. To understand the development of the atomic model. Let’s take this one step further…

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 Show video (3:36)

The Atom Today The model proposed by Niels 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 Show video (4:17)

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 2 x 12 = 2 electrons n = 2 2 x 22 = 8 electrons n = 3 Each principal level has a number of sublevels equal to the level number n = 1 1 sublevel n = 2 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 sublevel? Shape s 1 spherical p 3 peanut d 5 4 are double-peanut 1 is a donut-ringed peanut f 7 flower Show balloons

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

Constant Electron-Density Surfaces of the 3d Orbitals D level orbitals Each The D sublevel can hold 10 electrons. Each orbital holds 2 electrons with opposite spins                                                  

The F Sublevel The F sublevel has 7 orbitals Each orbital can hold 2 electrons with opposite spin The F sublevel holds 14 electrons

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 Before we proceed… 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

Aufbau Diagram

Orbital Diagrams A box stands for one orbital An arrow stands for one electron Each box (orbital) can only hold 2 arrows (electrons) or to show direction of spin *Note: There is some overlap of energy levels, so sublevels do not fill in exact numerical order.

Orbital Diagrams

Orbital Diagram for A Nitrogen Atom 1s 2s 2p 3s     

Orbital Diagram for A Fluorine Atom 1s 2s 2p 3s     

Orbital Diagram for A Magnesium Atom Mg 1s 2s 2p 3s      

Learning Check O1 Write the orbital diagram for the electrons in an oxygen atom.

Solution O1 Write the orbital diagram for the electrons in an oxygen atom. 1s 2s 2p 3s     

Learning Check O2 Write the orbital diagram for the electrons in an iron atom.

Solution O2 Write the orbital diagram for the electrons in an iron atom. 1s 2s 2p 3s 3p 3d              

Electron Configuration Once electrons have been placed in boxes, the electron configuration is written. Write the energy level and letter for every sublevel that holds electrons Use a superscript to indicate the number of electrons in each sublevel Example: for Mg – 1s2 2s2 2p6 3s2 Mg 1s 2s 2p 3s      

Exceptional Electron Configurations Filled energy levels are the most stable Half filled energy levels are the second most stable Copper, Chromium and Silver are very important examples of how “exceptions” to filling the Aufbaum diagram leads to understanding the charge of transition metals

Examples Write electron configurations for: P, Cr, Sn Now write the electron configuration without the boxes: Mg, Ni What element has the following electronic configuration: 1s2 2s2 2p6 3s2 3p1 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2 For fun at home: http://www.lon-capa.org/~mmp/period/electron.htm