Chapter 3 notes
Chapter 3 notes CHEM 100 002
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This 5 page Class Notes was uploaded by Heidi Archer on Sunday February 7, 2016. The Class Notes belongs to CHEM 100 002 at Indiana State University taught by Jeeewandara in Winter 2016. Since its upload, it has received 29 views. For similar materials see Chemistry and Society in Chemistry at Indiana State University.
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Date Created: 02/07/16
Chemistry Chapter 3 Notes Atomic Theory Develops Lavoisier: Law of Conservation and Mass o Mass vs. Weight? Mass: Measure of quantity of matter within it Weight: Measure of the gravitational pull of an object o Law of conservation of Mass: Matter is neither created nor destroyed in a chemical reaction Joseph Proust (French Chemist) o All Samples of a given compound have the same proportions of their constituent elements – always fixed ratios Daltons Atomic Theory All matter is composed of particles called : Atoms Ernest Rutherford Postulated that the atom consisted of a sphere of positive charge filled with small negatively charged particles called electrons Most of an atoms mass is contained in a small space called the nucleus The nucleus is composed of positively charged protons and neutral neutrons Most of atoms volume is empty space occupied by very tiny negatively charged particles called electrons The number of negatively charged electrons outside the nucleus is the same as the number of positively charged particles in the nucleus for electrically neutral atoms Atoms Incredibly small An atom is the smallest identifiable unit of an element Similarities and differences on the atomic scale correlate with similarities and differences on the macroscopic scale Protons Determine the Element The atomic number, Z, represents the number of protons in the nucleus of an atom o So if the elements atomic number is 5, the number of protons is also 5 The charge of the proton is assigned numerical value of +1 o Nitrogen has a 7 protons . . . so you add 1 (since value is +1) making the charge of the proton 8 Protons constitute a significant part of the mass of an atom o The mass of a proton is 1.0 amu o An amu is a unit of mass equivalent to 1/12 the mass of a carbon12 nucleus and is equivalent to 1.67 × 10 g Concept Check The graphite in a pencil and the gemstone diamond are composed entirely of pure carbon atoms. Even though these substances appear and behave very differently, what about the nucleus do these carbon atoms have in common that identify them as carbon? Diamonds and graphite are composed of carbon atoms with six protons in the nucleus Chemical Symbols Symbols are an abbreviation of the chemical name can be based on: o The English name for the element : Hydrogen is H o The Greek or Latin name: Ferrum (iron) is Fe o Their place of discovery : Europium is Eu o The scientist honored by the naming: Curium is Cm Elements All naturally occurring elements have probably been discovered New elements: do not exist naturally o Have been created by accelerating protons or neutrons into the nuclei of naturally occurring elements o All known elements are listed in the periodic table in order of increasing atomic number Electrons A neutral atom has as many electrons outside its nucleus as protons within its nucleus Opposing charges of protons and electrons hold electrons within a spherical region surrounding the nucleus Atoms can lose or gain one or more electrons Cations are positively charges ions Concept Check p=protons e=electrons ch=charge Mg Mg +2 p=12 p=12 e=12 e=10 o You change the electrons to 10 so you get a positive charge (+2) for the element 2 O O p=8 p=8 e=8 e=10 ch=0 ch=2 o You change the electrons to 10 so you get a negative charge (2) for the element Determining Protons and Electrons Neutrons Neutrons are almost as massive as protons but carry no electrical charge The number of neutrons in the atoms of an element can vary resulting in isotopes o Can be naturally occurring or manmade Isotopes: Atoms with different number of neutrons o Mass change is determined by isotopes Example: C C C4 p=6 p=6 p=6 n=6 n=7 n=8 Mass number of an atom The sum of neutrons and protons in an atom is called the mass number (A) of the atom (See bottom of notes titled Periodic Table for reference) o Example: p=2 e=2 n= (Mass Number – Protons) 2 How many protons Neutrons and electrons Decoding an element symbol o Where: Z is the atomic number A is the mass number C is the charge X is the symbol of the element Mass number is the sum of protons + sum neutrons Atomic number is the sum of the protons Number of neutrons is AZ Neutral atoms have equal numbers of protons and electrons 55.85 is the average atomic mass Finding Average Atomic Mass Example : Isotope 1 : Mg 23.99 amu (1amu=1.66054 × 10 g) (amu=atomic mass unit) Periodic Table In an element from the periodic table the number at the top represents the: atomic Number# of protons o So Helium atomic number is 2 . . . so the number of protons is 2 He represents the chemical symbol for Helium o Make sure to write accordingly: Helium’s symbol is He not HE Average atomic mass is at the bottom of the element (in this case it is 4.0026)
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