Lab Chem Notes Christopher McKay Chapter 4 Atoms Atoms 11 04 2014 Smallest unit that can exist alone or in combination with other atoms Greek word means indivisible Nucleus contains protons p Always positive and neutrons n0 Neutral Dense small Electron Cloud Contains electrons e Always negative Surrounds nucleus mostly empty space Arranged in shells or energy levels Number of p e Structure Measure is extremely tiny Ex Nucleus is a marble in a Stadium Amu Special unit for the mass of an atom Particle Proton Neutron Electron Symbol p n 0 e Charge 1 0 1 Mass Number 1 1 0 Definitions Atomic Number Number of p in the nclesu of an atom Always equal to number of e Big Blue Atomic Mass The average mass of the isotopes Little Red Mass Number Number of p and n 0 in the nucleus of an atom The Mass Number is the Atomic Mass rounded off to a whole number A Atomic Mass is the same as P Protons is the same as E Electrons Page Break M Mass minus A Atomic N Neutrons Percentage Amount of each part x 100 Amount of the total Percentage Abundance The percentage of an isotope Average The sum of a list of numbers The number of Numbers Weighted Average 1st number percentage 2nd number percentage 100 Average Weighted Mass 1st mass abundance 2nd mass abundance Isotopes Isotopes are atoms of the same element that have different masses All atoms given element contain the same number of protons they do not always contain same numbers of neutrons Isotopes of any given atom have the same number of protons but a different number of neutrons Because the mass number equals the sum of protons and neutrons in the nucleus each additional neutron increases the mass number An isotope same P same E Different n0 different mass number Normal carbon is Carbon 12 with 12 referring to the mass number of those carbon atoms Carbon 13 and Carbon 14 also exist with 13 and 14 referring t the mass numbers of those carbon atoms How many more neutrons do Carbon 13 and Carbon 14 have than Carbon 12 Writing Isotopes 2 ways 1 Nuclear Label Mass Number 12 13 14 6C 6 C 6 C 2 Text label Carbon 12 Carbon 13 Carbon 14 C 12 C 13 C 14 C 14 U 238 Electron Configurations The Quantum Mechanical Model of electrons within an atom says we cannot pinpoint where an electron is but we can get the probability of where the electron is Electron configurations Show how electrons are distributed within an atom Describes the average distance of an electron from the nucleus Energy increase as you move further from the nucleus Within each energy level electrons occupy the sublevels Sublevel Correspond to the different areas an electron can be located in an atom Represented by a letter Examples s p d f g h I etc S sublevel spherical P sublevel Dumbbell Infinity Sign D sublevel Clover F sublevel Double clover Energy Level 1 2 3 4 5 Atomic Orbital Types if Sublevels 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g Each sublevel is orientated differently in a 3 D space and each orientation is called an atomic orbital Atomic orbitals can hold only two electrons Type of Sublevel S P D F g of Atomic Orbitals 1 3 5 7 9 of Electrons in sublevel 2 6 10 14 18 Number of Electrons in Each Energy Level Energy Level 1 2 3 4 of Electrons in an Energy Level S 2 S P 2 6 8 S P D 2 6 10 18 S P D F 2 6 10 14 32 Electron Configurations Writing Configurations and Orbital Notations Recall an electron configuration is a method of indicating the arrangement of electrons in a particular element or ion Electrons fill the 1st energy level before the 2nd before the 3rd etc Within an energy level fills s p d then f Remember for a neutral atom P e atomic number Example Write the electron configuration for Hydrogen Hydrogen has 1e 1 electron It will be labeled 1s 1 Big 1 will represent the energy level n S represents the sublevel and the little 1 represents the number of electrons Example Write the electron configuration for Helium Helium has 2e 2 electrons It will be labeled 1s 2 Write the electron configuration for Lithium Lithium has 3e 3 electrons 1s 2 2s 1 Aufbau Principle The A Principle Electrons enter sublevels with the lowest energy first Example Write the electron configuration for Nitrogen Nitrogen has 7e 1s 2 2s 2 2p 3 Magnesium has 12e 1s 2 2s 2 2p 6 3s 2 For elements with more than 18 electrons sublevels are filled out of order BUT the lowest energy sublevels are still filled first See energy level diagram Potassium has 19e 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Cobalt has 27e 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 Iron has 26e Calcium 20 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Writing Orbital Notations Uses circles to represent atomic orbitals with a label underneath to indicate sublevel and energy level One electron Arrow facing up or arrow with circle around it Two electrons Going to have two arrows one facing up one facing down or circle with arrow facing up and down Circle represents an orbital Hydrogen 1S Lithium 1s 2s Nitrogen Pauli Principle Atomic orbitals can hold only 2 electrons at most and they must have opposite spins 11 04 2014 Hund s Rule In a sublevel with more than one orbital put one electron into each orbital before putting 2e into any one orbital Identifying elements from the e configurations or orbital notation Recall if an element is neutral of e of p Atomic 1s 2 2s 2 2p 6 10 e Neon Diagonal Rule 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g 6s 6p 6d 6f 6g 6h 7s 7p Go by diagonal arrows Homework Do five elements from five rows You can use Abbreviations Step 1 Find the Noble Gas before your element and write its symbol Step 2 Subtract the Noble Gas s electrons from your electrons Step 3 Fill in the many arrows Step 4 Write the results after the Noble Gas Abbreviations Examples MT 109 Rn 7s2 5s14 6d7 Examples AR 4s2 3d2 CL 17 NE 3s23p5 SR 38 KR 5s2 UUS 117 RN 7s2 5f14 6d10 7p5 Homework He 1s2 Li 1s2 2s2 Na 1s2 2s2 2p6 3s1 K 1s2 2s2 2p6 3s2 3p6 4s1 Rb 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 Valence Electron A valence electron is an OUTER electron reaches the surface of the electron cloud Only electrons interact with the outside world Other electrons don t When electrons interact with other stuff it s called a chemical reaction occurs The electrons in the highest energy level …
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