Download 01 Atomic Number Mass Isotopes

Atomic Number
Atomic Number, Mass Number,
Atomic Mass, and Isotopes
Atomic Number
 In
what way are hydrogen atoms
different from oxygen atoms?
 Elements are different because they
contain different numbers of protons
 The atomic number of an element is
the number of protons in the nucleus
of an atom of that element
Atomic Number
 The atomic number identifies the
element
 Since atoms are electrically
neutral:
#
Mass Number
total number of protons and
neutrons in an atom is known as
the atom’s mass number
 The
 mass
number = #p+ + #n0
mass number is always an
integer value
 The
protons (p+) = # electrons (e-)
Mass Number
looking up the atomic number
and the mass number on the
periodic table, you can:
 By
the number of protons,
neutrons, and electrons in every
atom
 determine
1
Calculating p+, n0, and e An
oxygen (O) atom has an:
 atomic
number of 8
 a mass number of 16
number = # p+
 Therefore, O has 8 protons
 Atomic
Calculating p+, n0, and ethat atoms are always
electrically neutral
 # e- = # p+
 Therefore, O has 8 electrons
 Recall
Calculating p+, n0, and e The mass number is equal to the
number of protons plus the
number of neutrons
 mass # = # p+ + # n0
 mass
 16
# - # p+ = # n0
–8=8
 Therefore
O has 8 neutrons
Sample Problems
Sample Problems
2
Isotopes
 Recall that there are actually 3
kinds of neon atoms. How do
these atoms differ from each
other?
 They have different numbers of
neutrons
Isotopes
 2010Ne: 10 p+, 10 e-, 10 n0
 2110Ne:
10 p+, 10 e-, 11 n0
 2210Ne:
10 p+, 10 e-, 12 n0
Isotopes
 Isotopes
are atoms that have the
same number of protons but
different numbers of neutrons
 There are 3 isotopes of hydrogen
 Each isotope has 1 proton in its
nucleus
Isotopes of Hydrogen
most common isotope of H is
called hydrogen-1 (protium). It has:
 The
1
proton
 1 electron
0
 11H
 Its
Isotopes of Hydrogen
 The second isotope of H is called
hydrogen-2 (deuterium). It has:
1
proton
 1 electron
 1 neutron
 21H
 Its
mass number = 2 (1 + 1)
neutrons
mass number = 1 (1 + 0)
Isotopes of Hydrogen
 The third isotope of H is called
hydrogen-3 (tritium). It has:
1
proton
 1 electron
 2 neutrons
 31H
 Its
mass number = 3 (1 + 2)
3