UNIT 2 - ATOMIC THEORY VOCABULARY: Allotrope Anion Atom Atomic Mass Atomic Mass unit (a.m.u.) Atomic number Bohr model Cation Compound Electron Electron Configuration Element Excited state Ground state Ion Isotope Kernel electron(s) Lewis Dot Diagram Mass number Neutron Nuclear Charge Nucleons Nucleus Orbital Proton Quantum Theory Valence electron(s) Wave-mechanical model OBJECTIVES: Upon completion of the unit you will be able to do the following: Understand that the modern model of the atom has evolved over a long period of time through the work of many scientists Discuss the evolution of the atomic model Relate experimental evidence to models of the atom Identify the subatomic particles of an atom (electron, proton, and neutron) Know the properties (mass, location, and charge) of subatomic particles Determine the number of protons, electrons, and neutrons in a neutral atom and an ion Calculate the mass number and average atomic weight of an atom Differentiate between an anion and a cation Identify what element the amu unit is derived from Define the term orbital Distinguish between ground and excited state Identify and define isotopes Write electron configurations Generate Bohr diagrams Differentiate between kernel and valence electrons Draw Lewis Dot Diagrams for an element or an ion 1
THE EVOLUTION OF THE ATOMIC MODEL Atom = Democritus = Dalton (1803) o o o o o o Known as the of the atomic theory Dalton invented the word as the basic unit of matter which were considered to be Dalton also claimed that all atoms of a given element are He also discovered that atoms of different elements have different Found that combining atoms of different elements formed Theory referred to as the theory (it looked like a simple sphere) *What does this name tell you about Dalton s atom? J.J. Thomson (1897) o While using a he discovered that the ray was deflected (due to a magnetic/electrical field) o From this discovery he concluded that atoms contain small negatively charges particles called o Theory famously referred to as the model because he visualized the being within the structure of the atom (just like raisin bread) o The of the rest of the atom (besides the electrons) was thought to be and 2
* Rutherford (1909) * o Experiment called the where he a thin piece of with a o Often referred to as the model o Most alpha particles went & some were o Two conclusions were therefore made: 1) most of the atom is 2) atoms have a, called the * Neils Bohr (1913) * o Proposed that the atom consists of a dense nucleus with found in o He therefore stated that each electron orbiting the nucleus must possess a to keep it in place within its orbital o Known as the model (looks much like our solar system) Wave-Mechanical/Cloud Model (Modern Present day model) o Developed after the famous discovery that energy is made up of BOTH & o Still the same dense positively charged o Electrons now have distinct amounts of energy and move in areas called or o have contributed to this theory o Different from the Bohr diagram now the location of the electron is based on within the orbital *3-dimensional model 3
Date: Scientist: Name of Model: Atomic Model Conclusion(s) Date: Scientist: Name of Model: Date: Scientist: Name of Model: 4
Date: Scientist: Name of Model: Atomic Model Conclusion(s) Date: Scientist: Name of Model: 5
VOCABULARY (of the Periodic Table) SUBATOMIC PARTICLES Subatomic Particle Charge Relative Mass Location Symbol How to Calculate Proton Neutron Electron 6
Let s Practice Calculating Subatomic Particles in Different Atoms: Symbol # Protons # Neutrons # Electrons Atomic Number Mass Number Nuclear Symbol 35 Cl 17 15 16 C-14 8 Mass number = Nuclear Charge = Nucleons = 7
ATOMS (neutral) VS. IONS (charged) Vocabulary Term Definition Example/Diagram Neutral Atom Ion Anion Cation 8
ISOTOPE = Example: Isotopes of Carbon (C-12, C-13, & C-14) 12 13 14 C C C 6 6 6 U-238 U-240 So why does Carbon have a mass of 12.011 on the Reference Table? This is carbon s ATOMIC MASS which is the average weighted mass of all naturally occurring isotopes of carbon (there exist three different isotopes of carbon in the atmosphere as seen just above) 9
Calculating Atomic Mass (for any element): Atomic Mass = the weighted average of an element s naturally occurring isotopes (abundance in decimal form) (mass of isotope 1) (abundance in decimal form) (mass of isotope 2) + (abundance in decimal form) (mass of isotope 3) Example 1 12 C = 98.89% of carbon in the atmosphere 13 C = 1.11% of carbon in the atmosphere Step 1: Multiply the mass of each separate isotope by its percent abundance (in decimal form!!!!!!!) Step 2: Add up the products of all the calculated isotopes from step 1. Example 2: The element Boron occurs in nature as two isotopes. Isotope mass percent abundance Boron 10.0130 amu 19.9% Boron 11.0093 80.1% 10
Example 3: Isotope of Hydrogen 1 H 1 2 H 1 3 H 1 Protium Deuterium Tritium Percent Abundance 99.0% 0.6% 0.4% ATOMIC MASS VS. MASS NUMBER 11
ELECTRON CONFIGURATIONS = a dashed chain of numbers found in the of an element box (see below); tells us the number of as well as the number of in each level (tells us how the electrons are arranged around the nucleus) **All electron configurations on the Periodic Table are NEUTRAL (p=e) Substance Magnesium Mg +2 Bromine Br -1 Barium *Lead Electron Configuration * shortcut allows you to cut out the first two orbitals to shorten the address Valence Electrons: electrons found in the shell or orbital; the number in the electron configuration Kernel Electrons: electrons (all non-valence electrons) Sulfur # valence e- Nitrogen # valence e- # kernel e- # kernel e- 12
Principle Energy Level (n) = electron energy levels that contain a certain number of ; each sublevel contains one a set number of Maximum # of electrons in an energy level = where n = # (or period #) Principle Energy Level (n) Maximum number of electrons ( ) 1 2 3 4 Sample question: What is the maximum number of electrons that can occupy the 3 rd principal energy level in any atom? BOHR DIAGRAMS (one method for expressing electron location in an atom or ion); MUST be drawn 1. Look up electron configuration of element at hand on Periodic Table (if you are working with an ion, add/subtract the proper amount of electrons from outer shell(s) of configuration) Example: Carbon is 2. Draw nucleus (with a circle) and notate correct amount of protons and neutrons inside 3. Using rings or shells (these are your orbitals), place the proper amount of electrons in their appropriate orbital(s) there should be as many rings/shells as dashed number in electron configuration 13
Carbon Fluorine Beryllium Al Li I Na + S -2 LEWIS (ELECTRON) DOT DIAGRAMS - a shorter way of expressing electron location; an Only illustrates! 1. Write the element s symbol 2. Retrieve electron configuration from Periodic Table. The last number in the configuration is the. 3. Arrange the valence electrons (DOTS) around the symbol using the following rules: Only two electrons maximum per side of the symbol (therefore no more than 8 total surrounding symbol 8 is great!) Always pair the first two If you have more than 2 valence electrons, deal them one at a time to the other three sides until you run out 1 2 X 4 7 4. If you are working with an ion you must adjust the valence electrons (add or subtract electrons) in the configuration before constructing your Dot Diagram be sure to draw your final diagram with the initial charge on the ion 14
Draw LEWIS ELECTRON-DOT DIAGRAMS for the following: Argon Phosphorus Carbon Beryllium Oxygen Aluminum Sodium Bromine Na +1 O -2 15
Ground State vs. Excited State *Notice that one electron from the 2 nd orbital has moved to the 3 rd orbital Ground State = electrons in possible (configuration found on ); electrons as physically possible ground state electron configuration for Li is Excited State = electrons are ( configuration found on PT) excited state electron configuration for Li could be Distinguish between ground state and excited state electron configurations below: Bohr Electron Configuration 2-1 2-0-1 1-1-1 2-7-3 2-8-2 2-8-8-2 2-8-17-6 2-8-18-8 2-6-18-1 2-5-18-32 Ground (G) or Excited (E) state? 16
The greater the distance from the nucleus, the greater the energy of the electron Ground excited Ground Excited energy is absorbed energy is released (in the form of light energy) When atoms their will shift to a energy level or. This is a very condition so the electrons will state energy level (or ) When they from the excited state to the ground state they release energy in the form of. Different elements produce different colors of light or. These spectra are for each element (just like a human fingerprint is unique to each person). We therefore use spectra lines to which element we have because each element gives off a characteristic bright line spectra. 17
What to Study for the Atomic Exam (Unit 2) Structure of the atom (role/nature of the nucleus and electrons etc.) Gold Foil Experiment (know what was observed and the conclusions that were drawn from these 2 observations) Orbit vs. orbital (what is the difference?) Location, mass, charge of protons, neutrons, and electrons in an atom (see chart in notes) Isotopes (same element; different number of neutrons or masses ex: C-12 & C-14) be able to identify them Nucleons (the subatomic particles found in the nucleus) Nuclear Charge (charge inside the nucleus; always positive and directly dependent on # protons) Chemical notations: where do we find the atomic #, mass #, atomic mass etc. Determining the number of protons, neutrons, and electrons (pne) in an atom or ion (use mass # or atomic mass rounded to whole number) remember that the # protons ALWAYS tell us the symbol/element we have Atomic mass weighted average mass of an element s naturally occurring isotopes (ex: C is 12.011) Ground state vs. excited state and the energy absorbed/released during electron movement (remember: light is emitted or seen when an electron jumps from an excited state back down to ground state or a lower energy level) Principle energy levels (orbitals) and the maximum # electrons found in each use 2n 2 formula Calculating average atomic mass given isotope abundances and masses The nucleus makes up pretty much all the mass in an atom therefore (mass #) = (#protons) + (#neutrons) Who performed the cathode ray experiment? What subatomic particle was discovered in this experiment? Atom vs. Ion (what is the difference?) Electron Configuration found below the atomic number on PTable (know how to write them for an atom or ion) Drawing Bohr models show all the electrons within an atom/ion and their location (construct nucleus & use shells or circles to place electrons) Lewis Dot Diagrams write element symbol and distribute dots around (draw only the valence electrons) 18