1.3 Understanding Atomic Mass. A Review: Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ nono +1.

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Presentation transcript:

1.3 Understanding Atomic Mass

A Review: Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ nono / x x

Structure of the Atom There are two regions: 1. The Nucleus: With protons and neutrons Positive charge Almost all the mass 2. Electron cloud Most of the volume of an atom The region where the electrons can be found

If the atom was the size of a stadium, the nucleus would be the size of: a marble.

Standard Atomic Notation Includes the symbol of the element, the mass number and the atomic number X Mass number Atomic number # protons + # neutrons mass number

Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number F 19 9 = 9 = 10 = 9 =

Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number Br = 35 = 45 = 35 = 80

Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number Na Sodium ion = 11 = 12 = 10 = 11 = 23

Isotopes Atoms of the same element can have different numbers of neutrons  This gives them different mass numbers.  They have the same atomic numbers.  They look, act and react the same. C-12 vs. C-14

Naming Isotopes Put the mass number after the name of the element Examples: Carbon-12 and Carbon-14 Uranium-235 and Uranium-238

Which isotopes are represented in this sketch?

Calculations of Average Atomic Mass Why is the mass number on a periodic table never a nice whole number?

Mass Number vs AverageAtomic Mass The Mass Number is specific to one isotope. The Average Atomic Mass is the calculated based on the abundance of each naturally occurring isotope of that element. The Average Atomic Mass is shown on Periodic Tables.

Average Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atoms. oxygen-16, oxygen-17 and oxygen-18 We are more concerned with average atomic mass, based on the abundance of each element in nature. We don’t use grams because the numbers would be too small. California WEB

Atomic Mass Unit (amu or u) This unit is used instead of grams. It is 1/12 of the mass of a carbon-12 atom.

Calculating averages You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? California WEB

Calculating averages Total mass = (4 x 50) + (1 x 60) = 260 g Average mass = (4 x 50) + (1 x 60) = 260 g 5 5 Average mass = 4 x x 60 = 260 g California WEB

Average mass = (4/5)50 + (1/5)60 = 52 g Average mass = (0.8)50 + (0.2)60 = 52 g 80% of the rocks weigh 50 grams 20% of the rocks weigh 60 grams We calculate atomic mass the same way.

Sample Problem Calculate the average atomic mass of copper if copper has two isotopes. 69.1% has a mass of u and the rest has a mass of u. Cu IsotopePercentAbundanceMass Cu Cu u

Radioactive Isotopes

Radioactive: –Capable of spontaneously emitting radiation in the form of particles and/or gamma rays Radioisotope: –A radioactive isotope of an element that occurs naturally or is produced artificially.

Radioisotopes Many elements have one or more isotopes that are unstable. Atoms of unstable isotopes decay, emitting radiation as their nucleus changes. The changes can happen quickly or slowly, depending on the isotope. Radiation emitted can be harmless or very dangerous to living cells.

Applications of Nuclear Science Radiology:Anthropology: Nuclear Reactors: