Atomic Structure Notes Subatomic Particles Subatomic Particles Atomic Number, Atomic Mass & Mass Number Atomic Number, Atomic Mass & Mass Number Symbols and Names of Elements Symbols and Names of Elements Isotopes Isotopes

Subatomic Particles Particle:SymbolChargeWherefound Relative Mass Actual Mass (g) Protonp++1nucleus 1 amu 1.67 x Neutron nonononoNeutral0nucleus1amu Electrone-outsidenucleus 1/1840 amu 9.11 x Question: What overall charge does the nucleus have? Answer: Positive!- due to the protons present Note: amu= atomic mass unit (equal to 1/12 a carbon atom) 4.2 Q. 6-8

The Basics Atomic Number (whole number) -number of protons in an atom -can equal electrons in a neutral atom -defines/identifies the atom Mass Number (whole number) -p+ plus n 0 -mass of the nucleus Atomic Mass (average-decimal) -average of all known isotope mass numbers for an element (This number will be closest to the most common isotope found in nature ) Isotope elements that have the same number of protons but different number of neutrons. 4.3 Q. 1-12

Periodic Table of Elements K 19 Potassium atomic # element symbol element name atomic mass Where is the mass number? 4.3 Q

Atomic Symbols There are two ways to represent elements: There are two ways to represent elements: Symbol: Symbol: # X # Mass Number (# of p + ) atomic # element symbol Name: Name: name of element followed by mass number. name of element followed by mass number. Ex... Ex... Carbon - 14 Carbon - 14 Aluminum - 27 Aluminum - 27 Nitrogen - 14 Nitrogen - 14 What are the Atomic Numbers for the above names? Mass Number =? _____________ # of p+ and n 0 Atomic number =13 Atomic number =7 Atomic number =6 4.3 Q

Atomic Calculations 31 31P element = _______________ element = _______________ Mass Number= ___________ atomic # = ______________ atomic # = ______________ # of p + = _______________ # of n 0 = _______________ # of e - = _______________ Phosphorus Manganese - 55 Manganese - 55 symbol = ______________ symbol = ______________ Mass Number = __________ Mass Number = __________ atomic # = ____________ atomic # = ____________ # of p + = ______________ # of n 0 = ______________ # of e - = ______________ Mn SymbolName #P+ #P+ and n Q

Isotopes - atoms of the same element with different # of n 0 !!! - atoms of the same element with different # of n 0 !!! Three isotopes of Carbon: Three isotopes of Carbon: Carbon - 14 Carbon - 14 Carbon - 12 Carbon - 12 Carbon - 13 Carbon - 13 (6p +, 6n 0 ) (6p +, 6n 0 ) (6p +, 7n 0 ) (6p +, 7n 0 ) (6p +, 8n 0 ) (6p +, 8n 0 ) element of life element of life extremely rare extremely rare radioactive…carbon dating radioactive…carbon dating Which of the following are isotopes of the same element? Which of the following are isotopes of the same element? 22 22X X X Neon - 20 Neon - 20 Neon - 22 Neon - 22 Magnesium - 22 Magnesium Compare to Atomic Mass Number: Same # of protons/atomic number 4.3 Q

Determining Average Atomic Mass The Average atomic mass (mass on the periodic table) is a weighted average of all the masses times their percentages added together. The Average atomic mass (mass on the periodic table) is a weighted average of all the masses times their percentages added together. Example Neon has 3 Isotopes (same element different mass) Example Neon has 3 Isotopes (same element different mass) Neon - 20, 90.92% of all Neon Neon - 20, 90.92% of all Neon Neon – 21, 0.257% of all Neon Neon – 21, 0.257% of all Neon Neon – 22, 8.82% of all Neon Neon – 22, 8.82% of all Neon

Determining Average Mass (Mass of Isotope A * % of A) + (Mass of Isotope B * % of B) + (Mass of Isotope C * % of C) = Average Mass (Mass of Isotope A * % of A) + (Mass of Isotope B * % of B) + (Mass of Isotope C * % of C) = Average Mass (20 *.9092) + (21 *.00257) + (22 *.0882) = = (20 *.9092) + (21 *.00257) + (22 *.0882) = = 20.18