Presentation is loading. Please wait. #  Atomic Number- the number of protons in the nucleus of an atom of that element  Ex: Hydrogen atoms have only one proton in the nucleus, so the atomic.

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 Atomic Number- the number of protons in the nucleus of an atom of that element  Ex: Hydrogen atoms have only one proton in the nucleus, so the atomic number is 1.  Atoms are neutral, so the # of protons =# of electrons.

 Total number of protons and neutrons in an atom.  Mass = # protons + # neutrons  The # of neutrons in an atom is the difference between mass # and atomic #.  # Neutrons = Mass # - Atomic #

 Atoms that have the same # of protons, but different # of neutrons.  If they have more/less neutrons, then the mass number will be different!  Have same number of protons and electrons. Only difference is # of neutrons!

 A way to measure the mass of an atom, using a standard (carbon-12).  Carbon-12 has 6 protons and 6 neutrons. It’s mass is set at 12 amu. So the mass of a single proton or neutron is about 1 amu.  Atomic Mass- weighted average mass of the atoms in a naturally occurring sample of the element.

 Ca  P -3  Al +3

1. Change abundance percents into decimals. 2. Multiply the mass of each isotope by its natural abundance. (expressed as decimal) 3. Add the products.

 Element X has two natural isotopes. The isotope with a mass of 10.012 amu has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu has a relative abundance of 80.09%. Calculate the atomic mass and identify this element.

 The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass = 62.93 amu, and 30.8% for mass = 64.93 amu. Calculate the average atomic mass of copper.

 Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).

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