Atomic Structure & Nuclear Chemistry Unit 3 Notes Academic Chemistry Name 52 24 Cr Mass Number Symbol Atomic Number Unit #3 Test Date You can never learn less, you can only learn more. R. Buckminster Fuller cincochem.pbworks.com
Atomic Theory Unit 3 With scientific method, the Greek philosopher first used the term to describe the smallest, indivisible unit of matter in around 400 BCE. Almost 2000 years later 1803 John Dalton First Atomic Model Matter is made of indivisible particles called Atoms of one element are Atoms of different elements are The atom is a solid mass. 1879 J.J. Thomson Plum Pudding Model Identified the as a particle Used a Crooke s tube to examine electrons - model Atom is a clump of charged material (pudding) with electrons scattered throughout (plums) 1911 Ernest Rutherford Nuclear Model experiment Shot particles through paper thin gold foil Most passed thru (atom is mostly ) Very few deflected greatly (dense + charged ) 2 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Atomic Theory 1913 Neils Bohr BOHR Model a.k.a planetary model electrons are arranged in concentric orbits (like rings) around the sun electrons have fixed an energy level is the region around the nucleus where electrons are moving 1925 Quantum Mechanical Model currently accepted model first proposed by Werner Heisenberg Many physicists & chemists contributed to model Mathematical model derived by Max Schrödinger the is the space where probability of finding electron is high Atomic & Nuclear cincochem.pbworks.com 3
Atomic Structure Unit 3 An atom is the (smallest unique) unit of matter. There are two regions of an atom that contain particles of matter, the rest is empty space. The nucleus, at the CENTER of the atom, holds: PROTONS ( charge) and; NEUTRONS ( charge) The electron cloud is a region SURROUNDING the nucleus where ELECTRONS ( charge) are found. The Periodic Table and How Atoms Differ Label Hydrogen s entry on the Periodic Table. 1 H 1.008 Hydrogen 4 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Atomic Structure The ATOMIC NUMBER is the number of PROTONS in an atom and: o Is unique to each element o o o Is THE SAME for all atoms of an element IDENTIFIES an element. In a neutral atom (equal # of negative and positive particles), the IS EQUAL TO the # of. The MASS NUMBER is the number of PROTONS plus the number of NEUTRONS in an atom and is the same as the mass of the Q: Why don t electrons get counted in the mass of an atom? A: The mass of an electron is negligible, about times smaller, when compared to the mass of a proton or a neutron, so electron mass is not counted in the mass number. The mass of atoms is measured in, or atomic mass units. 1 amu = the mass of 1 atom of carbon (carbon with a mass # of 12) Atomic & Nuclear cincochem.pbworks.com 5
Subatomic Particles and Isotopes Unit 3 Fill in the missing information about each subatomic particle: Particle Charge Where Mass In one element, found? (amu) can the # vary? proton + electron Yes, ions! neutron 0 Yes, isotopes! Fill in the following information about the selected atoms: # of Element Symbol Atomic # Mass # protons # of neutrons # of electrons Sodium Na 11 23 11 12 11 9 19 Se 45 Chromium 28 Ga 70 6 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Shorthand Notation Shorthand notation allows us to write a single isotope simply. When shorthand notation is used, it will appear one of the following ways: Example: Bromine with a mass number of 80 amu can be written: or Bromine has an atomic number of 35. The 80, above, is the mass number of this atom of bromine. SO, we now know that this bromine isotope has 35 protons and 45 neutrons. *79.90 on the periodic table is the average mass of all known Bromine atoms. number 35 Br 79.90 Bromine Atomic number atomic 80 35 Br PERIODIC TABLE (applies to all Bromine atoms) SHORTHAND notation (applies to one Bromine isotope) Practice: Write the shorthand notation for 1) Neon 22 2) Potassium 41 3) Chlorine 36 Atomic & Nuclear cincochem.pbworks.com 7
Isotopes Unit 3 Isotopes are atoms of the same element that have different numbers of. This means isotopes have different atomic masses but the same atomic number Isotopes of an element are chemically the same (because neutrons are neutral). All elements have isotopes. Every element found in nature is a mixture of all its isotopes Example: Three isotopes of potassium Potassium 39 Potassium 40 Potassium 41 P + P + P + E E E N 0 N 0 N 0 Q: Why aren t the masses listed on the periodic table whole numbers and why don t they match the mass numbers we have been using? A: Since ALL elements exist as many different isotopes (with different mass numbers), the mass on the periodic table is the atomic mass. 8 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Average Atomic Mass Average atomic mass is a weighted average of all isotopes of an element. The percent of each isotope in an element (all known atoms) is called its PERCENT ABUNDANCE. Every isotope has its own percent abundance. Example: Nitrogen has two naturally occurring isotopes, nitrogen-14 and nitrogen-15. The average atomic mass of nitrogen is 14.007 amu. Which isotope is more abundant in nature? Calculate Average Atomic Mass in a 3 step process. Example: lithium-7 (mass = 7.016 amu, 92.41%) lithium-6 (mass = 6.015 amu, 7.59%) Step 1: Change the percent abundance for each isotope to a decimal. (Move decimal 2 places to left to convert from percent to decimal) lithium-7 = 92.41% 0.9241 lithium-6 = 07.59% 0.0759 Step 2: Multiply each abundance value by the mass of the isotope. The product is called relative mass..9241 x 7.016 = 6.483 amu.0759 x 6.015 = 0.457 amu Step 3: Add the relative masses to find average atomic mass. Units are amu. 6.483 + 0.457 = 6.940 amu Atomic & Nuclear cincochem.pbworks.com 9
Average Atomic Mass Unit 3 Example: Find the average atomic mass of boron. boron-10 (% abundance = 19.8% and mass = 10.013 amu) boron-11 (% abundance = 80.2% and mass = 11.009 amu) Example: Silver is found in nature in the following percentages: 107 47 109 47 Ag = 51.82% Ag = 48.18% Calculate the average atomic mass of Silver. Practice: Rubidium has two common isotopes, 85 Rb and 87 Rb. If the abundance of 85 Rb is 72.2% and the abundance of 87 Rb is 27.8%, what is the average atomic mass of rubidium? 10 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Nuclear Chemistry and Stability In reality, all atoms will eventually break apart, given enough time. The time required for half of a sample of one isotope to break apart (spontaneously decay) is called its half-life. Some isotopes have a half-life of seconds; others have a half-life of billions of years (longer than the age of the universe!). When a nucleus decays, energy, and often particles (protons, neutrons and/or electrons) are ejected from the nucleus. ISOTOPE STABILITY An isotope is considered if the nucleus will NOT spontaneously decay. o Elements with atomic # have at least one isotope that is very stable 1:1 ratio of proton to neutron (p + : n 0 ) Example: Carbon-12 has 6 p + and 6 n 0 o Elements with atomic # have at least one isotope that is somewhat stable (still stable!) 2:3 ratio of protons to neutrons (p + : n 0 ) Example: Mercury-200 has 80 p + and 120 n 0 o Elements with atomic # do not have a stable isotope and are unstable AND radioactive 1: >2 ratio of protons to neutrons (p + : n 0 ) Examples: Uranium (U) and Plutonium (Pu) An isotope with an unstable nucleus is called a radioisotope. Atomic & Nuclear cincochem.pbworks.com 11
Nuclear Decay / Alpha Decay Unit 3 An unstable nucleus decays because it has a number of neutrons, either too many or not enough, that makes the nucleus unstable. The decaying nucleus emits energy as particles and rays and transmutates into a more stable isotope of a different element. There are many types of decay. Alpha () Decay emission of an alpha particle, denoted by the symbol to the RIGHT because contains protons & neutrons (like a Helium nucleus). The charge is because it has protons. Alpha decay the mass number by and the atomic number by. There are NO electrons in an alpha particle All nuclear equations are balanced Example: Write the nuclear equation for the radioactive decay of polonium-210 (Po) by alpha emission. Practice: Write the balanced nuclear equation for the alpha decay of radium-226. 12 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Beta Decay Beta () Decay emission of a beta particle, a fast-moving electron given by the symbols at OR right. particles have insignificant mass, so mass # = 0 decay results from the conversion of a neutron into a proton in the nucleus. In this process, a high speed electron is ejected from the nucleus. The charge of the particle is (just like an electron) Beta decay causes change in the mass number. The atomic number by 1. Example: Write the nuclear equation for the radioactive decay of carbon-14 by beta emission. Practice: Write the balanced nuclear equation for the reaction in which zirconium-97 undergoes beta decay. Atomic & Nuclear cincochem.pbworks.com 13
Gamma Radiation & Uses of Radioisotopes Unit 3 Gamma (γ) Emission high-energy ELECTROMAGNETIC RADIATION denoted by the symbol at right. No particles included, only energy, so no change in contents of nucleus. Charge is. effect on mass number or atomic number, so not included in nuclear reactions. Gamma rays always accompany alpha and beta radiation. Uses of Radioactive Isotopes All three types of radiation are used beneficially in the following ways: Medical imaging, treatment, research and diagnostics Food irradiation to kill harmful bacteria Smoke detectors Biological research and studies Insecticides Energy Production Numerous Industrial Applications transmutation the conversion of an atom of one element to an atom of another element (radioactive decay is one way that this occurs!) 14 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Properties of Particles and Radiation Properties of Particles and Radiation Alpha () Beta () Gamma () Composition Helium nucleus 2p +, 2n o High energy electron High-energy electromagnetic radiation Charge + 0 Change in Mass Number Change in Atomic Number Decrease by no change no change Decrease by Increase by no change Mass (amu) 4 0 Tissue Penetrating power (depth of travel) Low (0.05 mm) Moderate (4 mm) Very High (penetrates entire body easily) Shielding (to stop progress of radiation) Sheet of paper Wood Metal foil Lead Concrete Atomic & Nuclear cincochem.pbworks.com 15
Types of Nuclear Reactions Unit 3 In a NUCLEAR reaction, the following will occur isotopes of one element are CHANGED into isotopes of another element ( ) contents of the nucleus change amounts of energy are released There are FOUR types of nuclear reactions. 1. Radioactive Decay alpha decay, beta decay, and gamma electromagnetic radiation 2. FISSION a nucleus a. A very nucleus is split into two large fragments by a fast moving neutron. 9 U + neutron Kr + 6Ba + neutrons + energy 6 9 44 b. The reaction releases lots of and many which split more nuclei 16 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Types of Nuclear Reactions Above: Fission of Uranium 235 c. If controlled, energy is released like in a nuclear reactor, and can be turned into electricity. d. If not controlled or control is lost, a nuclear explosion or reactor meltdown can occur e. 1 st controlled nuclear reaction 1942 (Chicago Pile-1 created by Enrico Fermi) f. 1 st atomic bomb explosion 1945 (Trinity Bomb Test in White Sands, NM) 3. FUSION of nuclei two nuclei combine to form single larger nucleus 4 H + H He + neutron + energy Atomic & Nuclear cincochem.pbworks.com 17
Types of Nuclear Reactions Unit 3 Does NOT occur under standard conditions, positively charged Hydrogen atoms each other. advantages (compared to fission) - inexpensive, no radioactive waste disadvantages - requires amounts of energy to start reaction and is difficult to control examples energy output of stars, modern thermonuclear weapons (hydrogen bombs), future nuclear reactors Above: Fusion of Deuterium and Tritium 4. Nuclear Disintegration Emission of a or a. Occurs when very small particles hit a nucleus with enough energy to remove particles. 18 cincochem.pbworks.com Atomic & Nuclear
Unit 3 Terms Atomic number number of protons in an atom or element. In a neutral atom equals the number of electrons Mass number the total number of protons and neutrons in the nucleus of a single atom of one element. Atomic mass the mass of one isotope of an element. Numerically will always be the same as mass number. Average atomic mass the average mass of all isotopes of an element in earth s crust and atmosphere. This number is listed on the periodic table and YOU know how to calculate it! Atomic & Nuclear cincochem.pbworks.com 19
PTable Unit 3 20 cincochem.pbworks.com Atomic & Nuclear