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.

ex-

Ne-20

10p+ 10e- 10n0

Ne-21

10p+ 10e- 11n0

Ne-22

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 abundant

-is a %

-the element that is most abundant is the one that has a mass closest to the atomic mass

ex-

Cu-63 or Cu-65

Which is most abundant?

Cu-63 b/c its mass is closer to atomic mass