Transcript Unit VIII: Atoms and The Periodic Table

Unit II:
Atoms and The
Periodic Table
ATOMIC NUMBER, ATOMIC
MASS, AND ISOTOPES
Subatomic Particles

Particles which make up the atom
are called subatomic particles.
Atom: Nucleus
Protons
Neutrons
Atom: Nitrogen
Electrons
Energy
Levels
Ordinary
Hydrogen
Tritium
Deuterium
Isotopes

Isotopes are:

Different forms of the same element
with the SAME # of Protons but
with DIFFERENT #’s of Neutrons
Mass Number

Mass Number = Total Protons +
Neutrons in an isotope of an
element
Mass Number
P+N
1 P + 2 N’s
3H
Also called “Hydrogen – 3”
Mass Number
3H
Called Nuclear Notation
Practice Problem

To find P’s and N’s from Nuclear
Notation
Mass # = P + N
To find # of
Neutrons, put
Atomic Number
Here:
Subtract to get #
of Neutrons
41
Ca
20
21
Calcium’s atomic
Number = 20
20 Protons
So it has 21 Neutrons
Find the # of Protons and # of Neutrons in
Each of the Following Isotopes:
Find the # of Protons and # of Neutrons in
Each of the Following Isotopes:
Now Try the Other Way
Now Try the Other Way
Now Try the Other Way
Now Try the Other Way
Neutral Atom

In a Neutral Atom of an Element:

The # of Electrons(-) = The # of
Protons(+)
Ion

An ion is an atom where:


# of p’s
In a + ion (cation)


# of e-’s ¹ ≠
# of e-’s
<
# of p’s
In a - ion (anion)

# of e-’s
>
# of p’s
Example #1

The ion Ca 2+

has 20 protons (atomic #) and it has
18 e-’s (2 less –’s than +’s, hence a
2+ charge)
Example 2

The ion Se 2-has 34 protons (atomic
#) and it has 36 e-’s (2 more –’s than
+’s, hence a 2- charge)
Example 3

An atom of Bi has 83 protons (atomic
#) and it has 83 e-’s (e-’s are equal to
protons, hence, no charge (neutral))
Isotopes Continued
The isotope:
 56Fe 3+
 has 26 protons
 30 neutrons (56-26)
 23 electrons (26-3)

Isotopes Continued
The isotope:
 76As 3 has 33 protons
 43 neutrons (76-33)
 36 electrons (33 +3)

Isotopes Continued
The isotope:
 201Au+
 has 79 protons
 122 neutrons (201-79)
 78 electrons (79 - 1)

An isotope has 46 protons, 58
neutrons and 42 electrons.
Write the nuclear notation:

Answer: 104Pd 4+
An isotope has 52 protons,
79 neutrons and 54 electrons.
Write the nuclear notation:

Answer: 131Te2-
Finding (average) atomic mass
using isotope abundances

Assumption: Assume


mass of a neutron = mass of proton =
1 u (atomic mass unit)
this is not “exactly” correct
The mass of a proton = 1.007276 u
 The mass of a neutron = 1.00866 u

Example #1



Chlorine in nature is 75.77% 35Cl and 24.23% 37Cl
Using these: Find the average atomic mass of Cl
Change % to decimals