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 Calculate the number of protons, neutrons, and electrons in an atom given its mass number and atomic number.  Define an isotope and explain why atomic.

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Presentation on theme: " Calculate the number of protons, neutrons, and electrons in an atom given its mass number and atomic number.  Define an isotope and explain why atomic."— Presentation transcript:

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2  Calculate the number of protons, neutrons, and electrons in an atom given its mass number and atomic number.  Define an isotope and explain why atomic masses are not whole numbers.  To calculate how we get atomic masses of elements with isotopes.

3 1. Find the element on the periodic table. 2. Find the Atomic Number of the element. 3. Atomic Number = # of protons in the element. * Remember the # of protons of an atom determines what element it is representing.

4  How many protons do the following elements have? 1. Oxygen 88 2. Zinc  Bismuth  83

5  Atomic Mass = protons + neutrons  If we know the # of protons from the Atomic Number, then … Atomic Mass - # of protons = # of neutrons *Remember you should take the atomic mass on the periodic table and round it first

6  Oxygen 1. Atomic Mass from the Periodic Table:  > Subtract the # of protons (Atomic Number) from the Atomic Mass  16 – 8 = 8 *There are 8 neutrons in a neutral oxygen atom.

7  In a neutral atom, there must be the same number of positive and negative charges. Therefore…  # of protons = # of electron  The # of electrons = Atomic Number.

8  Atoms that have the same number of protons but different numbers of neutrons.  They will have the same Atomic Number but different Atomic Masses.

9  In nature most elements are found as a mixture of isotopes.  No matter where a sample of an element is obtained, the relative abundance of each isotope is the constant.  Example: In a banana there is 93.25% potassium with 20 neutrons, % have 22 neutrons, and % have 21 neutrons.

10 39  Potassuim-39 or K-39 or 19 K protons-19 electrons-19 neutrons-20

11 *Both protons and neutrons are very close in mass to 1 amu. *Atomic Mass Unit = 1/12 the mass of carbon-12 Masses of subatomic Particles ParticleMass (amu Electron Proton Neutron

12  We take weighted averages of those elements based on the abundance of the isotopes.  Weighted Average = mass of isotope x percent abundance (decimal form) Then add the values that each isotope gives.

13  Element X has 2 natural isotopes. The isotopes with mass amu has a relative abundance of 19.91%. The isotope with mass amu has a relative abundance of 80.09%. What is this element? 1. Calculate the average atomic mass. 2. Compare this mass to the Periodic Table to find your element.

14 Isotope A: mass = % Isotope B: mass = % A: x.1991 = B: x.8009 = Now Add them: = 10.81amu Average Atomic Mass for Element X = amu


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