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# Basic particle descriptions - PowerPoint PPT Presentation

Basic particle descriptions. atom – the fundamental unit of which elements are composed (neutral: p + = e - ; n 0 varies) ion – atom that has lost or gained electrons and carries a charge ( p + ≠ e - ; n 0 same)

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Presentation Transcript

• atom – the fundamental unit of which elements are composed (neutral: p+ = e-; n0 varies)

• ion – atom that has lost or gained electrons and carries a charge (p+ ≠ e-; n0 same)

• isotope – atoms of the same element that have different numbers of neutrons (protons equal, but neutrons unequal)

• An isotope refers to a group of atoms within each element with a specific mass number.

• Every atom is an isotope.

• Isotopes are referred to by their mass number; eg. carbon-12 or uranium-238

Diagram

Instrument

amu – atomic mass unit

• 1 amu = 1/12 of a carbon-12 atom

• Approximately = 1 proton or neutron

• Approximately = 1.66 x 10-27 kg

• amu is useful on an atomic scale, but we will use units in class that are equivalent and more meaningful to the sizes we handle: grams/mol (g/mol)

Calculating atomic mass(weighted average)

• Turn each percentage into a decimal number.

• Multiply each mass by its matching decimal number.

Bromine has two isotopes with the first having a mass of 78.91 amu and occupying 50.69% and the second isotope having a mass of 80.91 amu and occupying 49.31%. What is the average atomic mass of bromine?

0.5069(78.91 amu) + 0.4931(80.91 amu) =

79.90 amu = 79.90 g/mol

Verify the atomic mass of chlorine using this data for its two isotopes:

chlorine-35 = 34.96 amu;

percent abundance = 75.77%

chlorine-37 = 36.96 amu

percent abundance = 24.23%

0.7577(34.96 amu) + 0.2423(36.96 amu) =

35.44 amu = 35.44 g/mol