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Ch. 2 Notes - Atoms and Elements

by: N/A Notetaker

Ch. 2 Notes - Atoms and Elements CHM 2023

Marketplace > University of South Florida > Chemistry > CHM 2023 > Ch 2 Notes Atoms and Elements
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Chem for Today
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This 3 page Class Notes was uploaded by N/A Notetaker on Sunday October 18, 2015. The Class Notes belongs to CHM 2023 at University of South Florida taught by Cruz in Summer 2015. Since its upload, it has received 9 views. For similar materials see Chem for Today in Chemistry at University of South Florida.


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Date Created: 10/18/15
23 Modern Atomic Theory and Laws that lead to it Law of conservation of mass in a reaction matter cannot be created nor destroyed total mass does not change What you start with is what you end with Law of de nite proportions all samples of a compound regardless of their sourcepreparation have same proportions of their constituent elements Ex 16 g 024 g H2 164 41 ratio Ex 12 g 02 3 g H2 123 41 ratio Law of multiple proportions When two elements form two different compounds masses of one element combine with 1 g of another element can be expressed as a small who number ratio ExMassof1gCinCO24gMassof1gCinCo2g42 2 Dalton s Atomic Theory 1 Each element is composed of particles caed atoms 2 All atoms of given element have same mass and properties that make them different than atoms of another element 3 Atoms combine in simple whole number ratios to form compounds 4 Atoms of one element cannot became atoms of another element 24 The Discovery of the Electron In a cathode ray tube particle beams caed cathodes traveled from negative charged electrode cathode to positively charged called anode The particles travel in straight lines independent of material from which they originate from and carry a negative electrical charge Electrical charge property of some particles that compose atoms and result in attractive and repulsive forces between particles Where these forces exist is called electrical eld Electron negatively charged low mass particle in all atoms Mass of electron 91010quot28 kg 25 Structure of Atom Nuclear theory has three parts 1 Most of atoms mass and its positive charge is contained in small core caed nucleus 2 Most volume of atoms is empty space where negatively charged electrons oat 3 There is an equal amount of negatively charged electrons and positively charged particles called protons within nucleus so atom is neutral 26 Subatomic Particles mass of proton 16726210quot27 kg mass of neutron 16749310quot27 kg amu common unit to express mass 112 mass of carbon atom containing six protons and six neutrons amu for both proton and neutron is approx 1 amu proton and electron have electrical charge matter is usually neutral because protons and electrons are present in equal number atomic number Z number of protons in an atoms nucleus chemical symbol one or two letter abbreviation of element isotopes atoms with same number of protons but different numbers of neutrons some only have one naturally occurring isotopes Be Al some have two Ne Cl mass number number of protons and neutrons XA chemical symbol or name mass number lons atoms can lose or gain electrons and gain charged particles Cations positively charged ions Anions negatively charged ions 27 Finding Patterns Periodic law when elements are arranged in order of increasing mass certain sets of properties recur periodically Metals lower left side and middle of periodic table good conductors of heat and electricity malleable ductile shiny tend to lose electrons when undergo chemical changes ex Pb Cu Nonmetals upper right side some are solid at room temperature others liquid or gases as whole poor conductors of electricity and gain electrons during chemical changes Ex 0 C Metalloids lie along zigzag diagonal line B Si Ge As Sb Te At exhibit mixed properties and are semiconductors Each column within main group region is family or group 8A noble gases mostly unreactive 1A alkali metals reactive metals 2A alkaline earth metals fairly reactive 7A halogens very reactive nonmetals a main group metal tends to lose electrons cations with same number of electrons as nearest noble gas main group nonmetal tends to gain electrons anions with same number of electrons of nearest noble gas Ex Li metal with 3 electrons lose 1 electrons to force 1 cation same number of electrons 2 as helium 28 Atomic Mass Atomic mass average mass for each element 29 Molar Mass Mole a chemists dozen 1 mol 6022amp10quot23 particle 602210quot23 is known as avogadro s number Value of mol is equal to number of atoms in exactly 12 grams of pure carbon12 Molar mass an elements molar mass in grams per mole is numerically equal to element s atomic mass in amu


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