Chapter 5 Sections 2 and 3
Structure of an atom
nucleus- center of an atom
-discovered by Ernest Rutherford in 1911
proton (p+)
-positively charged subatomic particle
-found in the nucleus of an atom
-discovered by Eugen Goldstein in 1886
-mass= 1.67 X 10-24g
neutron (n0)
-subatomic particle with no charge
-found in the nucleus
-discovered by James Chadwick in 1932
-mass= 1.67 X 10-24g
electron (e-)
-negatively charged subatomic particle
-found surrounding the nucleus in energy
levels or electron clouds
-discovered by JJ Thomson in 1897
-mass= 9.11 X 10-28g
*atoms are electrically neutral because:
# of p+ = # of e-most of the mass is in the nucleus of that atom
atomic number- number of protons in the
nucleus of an atom
(smaller number on the periodic table)
-also = # of electrons b/c of above *
mass number- total number of protons and
neutrons in an atom
-larger number on periodic table
-must be rounded to a whole number
# of n0 = mass # - atomic #
-element can be written as He-4
isotope- atoms of the same element having the
same # of p+ and e-, but different # of n0.
10p+ 10e- 10n0
10p+ 10e- 11n0
10p+ 10e- 12n0
atomic mass- average mass of all the isotopes of
an element
-bigger number on periodic table unrounded
-units are amu (atomic mass unit)
relative abundance- which isotope is more
-is a %
-the element that is most abundant is the one that
has a mass closest to the atomic mass
exCu-63 or Cu-65
Which is most abundant?
Cu-63 b/c its mass is closer to atomic mass

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