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The Atom
Unit III
Picture it….
Draw a picture of a Helium particle and a Xenon particle.
Similarities: Both are atoms.Difference? Mass
He: 4.0 g/moleXe: 131 g/mole
Why???
Xenon has more stuff in it. So, what’s in an atom?Protons = positive charge =p+
Electrons = negative charge = e-
Neutrons = neutral charge = n0
Now, draw a picture of the Helium atom, show how the subatomic particles are arranged.
The Helium Atom
= proton
= neutron
= electron
Atomic Number (Z):Identifies the element.Number of protons. Whole number (Blue) on periodic table.For a neutral atom the # of protons is equal to the number of electrons.
ISOTOPES: Atoms that have the same number of protons but different number of neutrons.Mass Number (A):
Unique for each isotope. Number of p+ + number of no
Not found on periodic table.C-12 vs. C-14
Identify the # of subatomic particlesElement #
protons# electrons
Mass # Atomic # #neutrons
Li 7
Ca 20
46 62
15 31
Atomic Mass:Also called atomic weight or molar mass.Weighted average mass for one mole of all isotopes.Decimal number found on P.T.
Atomic Mass = (mass1)(relative abundance1) + (mass2)(relative abundance2) +………..
Example: Calculate the atomic mass of chlorine. The two isotopes have atomic masses and relative abundance of 34.97 amu (75.77%) and 36.97 amu (24.23%).
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