Chapter
4/Lesson 3
Elements, Isotopes, and Ions
Element
A
pure substance made from atoms that
all have the same number of protons
 All atoms of the same element have the
same number of protons
Atomic Number
 Represents
the number of protons in the
atoms nucleus
 The periodic table is arranged in
ascending order of atomic numbers
Mass Number
 The
sum of the number of protons and
neutrons an atom has in it’s nucleus
 Atomic
number + the number of
neutrons= the mass number
How to find the number of
neutrons in the nucleus
 Mass
# - Atomic # = the number of
neutrons
 Example
 C14
– 6(atomic number) = the number of
neutrons
isotopes
 Atoms
of the same element have
different numbers of neutrons in the
nucleus
 Example…C12,
 All
C13, C14
versions of carbon have the same
number of protons
Average atomic mass
 The
weighted average mass of all the
known isotopes of an element
ion
 An
atom that is no longer neutral
because it has gained or lost an electron
 Positive
ions-Losing electrons
 Negative ions-gaining electrons