Name Chemistry-PAP Period. Notes: Electrons. Light travels through space as a wave. Waves have three primary characteristics:

Transcription

1 Name Chemistry-PAP Period The Wave Nature of Light Notes: Electrons Light travels through space as a wave. Waves have three primary characteristics: Wavelength (λ): the distance between 2 consecutive crests or troughs. Often measured in meters. Frequency (ν): the number of wave cycles (successive crests or troughs) that pass a given point per unit of time. Often measured in cycles per second ( s or Hertz). Speed (c): a constant for all forms of light; c =.00 x 0 8 m/s The Electromagnetic Spectrum: The speed of light, wavelength, and frequency are related by this formula: Wavelength and frequency are proportional

2 The Particle Nature of Light Not all properties of light can be explained by the wave model. Max Planck and Albert Einstein refined our understanding of light to include its particle nature. Light can be described as a stream of particles called photons. The details of the particle nature of light will not be investigated in this class. We will only highlight the relationship between the energy of light and its frequency: h = Planck s constant = x 0 4 J. s Energy and frequency are proportional. All atoms absorb and emit light when excited by electricity or heat Elements emit light in unique, distinct patterns called Spectra corresponds to the movement of electrons between Spectra are like fingerprints that can be used to an element (Flame Test Lab) The atomic orbital where the electron normally resides is known as its state. The atomic orbital that the electron moves to when it absorbs energy is known as its state. 2

3 Review of Quantum Mechanical Model (926) (currently accepted model of the atom) Mathematical model No defined path for electrons, but electrons are restricted to certain allowable energies within their atomic orbitals We can estimate the of finding an electron in a certain position The electron cloud is more where probability of finding electron is high The cloud is the most dense at the because all of the orbitals are centered on the nucleus Structure of the Electron Cloud Quantum mechanical model designates energy levels of electrons, using positive integer values (n). Energy levels are assigned values in order of increasing energy (n=, 2, ) As distance from nucleus increases, n Within each energy level, electrons occupy 4 types of sublevels exist:,,, and. Regions where electrons are likely to be found in the sublevel are called (or just orbitals ). Each orbital can hold a maximum of electrons. Number and kinds of orbitals depend on energy sublevel: s has, p has, d has, and f has orbitals Different orbitals have different (examples of s, p, and d orbitals below) s orbital makes up the s sublevel p orbitals make up the p sublevel d orbitals make up the d sublevel

4 This diagram shows how the s, 2s, and 2p, and s orbitals are arranged around the nucleus. All of the orbitals center on the nucleus and overlap there; this is why the probability of finding an electron increases, the closer you get to the nucleus. Summary of Energy Levels and Sublevels Energy Level #of Sublevels Type of sublevel # orbitals #electrons n= s n=2 2 2s 2p n= s p d n=4 4 4s 4p 4d 4f n= 4 s p d f n=6 6s 6p 6d n=7 2 7s 7p It is theoretically possible to have even more energy levels (and sublevels) than what is listed here; the table shows all that is necessary to describe the largest atoms on the periodic table. Electron Configuration An electron configuration shows the location (energy level and sublevel) for every electron in a given type of atom. Example: the electron configuration for lithium is s 2 2s. Lithium has electrons total: 2 electrons that occupy the s sublevel, and electron in the 2s sublevel. (superscripts equal the # of electrons in each sublevel) rules govern the filling of the atomic orbitals:. Aufbau Principle Electrons enter orbitals of energy first (various orbitals within a sublevel of an energy level are all considered to have equal energy) 7 7 4

5 Orbital energies sometimes deviate from the expected pattern Example: the 4s orbital has a lower energy than the d orbitals, even though they are on a higher energy level. This is due to the relative difficulty of an electron occupying a d orbital compared to an s orbital. The order can be depicted with an diagram. The arrow below labeled Increasing Energy shows the filling of the sublevels from lowest to highest energy. YOU WILL LEARN TO USE THE PERIODIC TABLE TO DERIVE THE AUFBAU ORDER. IT IS NOT TO BE MEMORIZED. 2. Pauli Exclusion Principle an orbital can only hold electrons (max) electrons in the same orbital must have spins; this decreases repulsions between electrons sharing an orbital usually shown as or. Hund s Rule when electrons fill orbitals of energy, an electron enters each orbital until all orbitals have electron. Only then are the electrons. Ex.: 4 electrons filling the three 2p orbitals would fill as follows:

6 Using the Periodic Table to derive the Aufbau order: Note the location of the s, p, d, and f sublevels, corresponding to blocks on the table. Read the table from top to bottom, left to right, going in order of atomic number. This will generate the Aufbau order for you. Careful with the f-block; remember to go in order of atomic number. (Ex. 4f fills after 6s) Practice: Electron Configurations Use the Periodic Table to write electron configs for the following atoms/ions: a) C h) Y b) Ne i) As c) Ca j) Zn d) P k) Mg 2+ e) V l) O 2- f) Br m) F g) K n) Na + Exceptions to the pattern: Cr s 2 2s 2 2p 6 s 2 p 6 4s d (same idea for other elements in group 6 -- s d ) Cu s 2 2s 2 2p 6 s 2 p 6 4s d 0 (same idea for other elements in group -- s d 0 ) these arrangements give chromium a half-filled d sublevel and copper a filled d sublevel filled energy levels are more than partially filled ones half-filled energy levels are more than partially filled as well 6

7 Noble Gas Notation (abbreviation or shortcut method) you can simplify an electron configuration by using the symbol for the in the period preceding the element to represent the configuration up to that point Ex. : Write the electron configuration for strontium using noble gas notation Ex. 2: Write the electron configuration for tin using noble gas notation Ex. : Write the electron configuration for bismuth using noble gas notation Ex. 4: Write the electron configuration for xenon using noble gas notation Note: the noble gases have completely filled outer s and p sublevels. This is what gives them their stability. More on this later! Practice. Use noble gas notation to write the e- configuration for a) cesium b) lead 2. Identify the following elements: a) [Ne]s 2 b) [Kr]s 2 4d Orbital Diagrams Orbital diagrams give a visual depiction of electron configuration They show more detail than an electron configuration, because they show the individual orbitals of each sublevel. an atomic orbital is represented by: or electrons are represented by arrows Ex : Draw the orbital diagram for the electrons in an oxygen atom: (do electron config first) Now draw orbital diagrams for: Fluorine Manganese 7

8 Valence Electrons Valence electrons are the electrons in the occupied energy level of an atom The valence electrons largely determine the properties of an element The valence electrons are involved in chemical (reactions) For our purposes, the number of valence electrons equals the number of electrons in the and sublevels of the highest energy level for that atom Ex.: Find the number of valence electrons for elements a g on p. 6 of the notes Do you notice a relationship between the valence electrons and the Roman numeral labels on the groups? (this trick works for representative elements only: s and p block elements) Electron Dot Structures electron dot structures show valence electrons as surrounding the chemical of the element dots are placed symmetrically around the element symbol, starting with one on each of the 4 sides, and if more than 4, then the dots are as needed. Ex: electron dot structure for a) calcium b) chlorine c) argon d) carbon Note: electron dot structures will be the same for every element in a. This is because all elements in a group have the same number of, leading to similar chemical properties. Connection to Ionic Compound Formation Use electron dot structures and arrows to show how the ionic compound forms between: ) Sodium and chlorine 2) Magnesium and fluorine ) Aluminum and sulfur All of this leads us to one of the basic tenets of chemistry called the rule: 8