Download Isotopes File - Northwest ISD Moodle

An atom has 13 protons, 13
neutrons, and 13 electrons.
Another atom has 13 protons, 14
neutrons, and 13 electrons
.
Analyze and explain how these
two atoms are related.
Explain what happens to an
atom when protons are added
or removed from its nucleus.
C. Johannesson
Isotopes
• Dalton’s Atomic theory was changed.
• Atoms of the same element can be
different, called isotopes.
Student Exploration
 How can isotopes of a given element
be identified?
 What is the difference between
atomic mass and atomic number?
C. Johannesson
Let’s Discuss
 How are the atoms of the isotopes of a given element




similar?
How are the atoms of the isotopes of a given element
different?
How are the atoms of the three isotopes of hydrogen
similar?
How are the atoms of the three isotopes of hydrogen
different?
By what reasoning would you conclude that the
masses of different isotopes of the same element
would differ?
Applying Parts of the Atom
When it comes to fighting cancer, doctors face two questions.
Where has the cancer spread? And how can it be treated? In the
case of one type of cancer, the answer to both questions may
involve the isotope iodine-131. Iodine-131 is an artificial isotope of
iodine. This isotope releases radiation that can kill cancer cells,
especially those that originated in the thyroid gland. Why does
iodine-131 target these particular cells? One job of the thyroid
gland is to produce a substance that helps the body regulate some
of its activities. Molecules of this substance contain natural iodine
atoms (iodine-127) that are normally absorbed by the body from
foods. Put another way, iodine supplied by nutrients becomes
concentrated in the thyroid gland and its cells. Normally, this is a
good thing since thyroid cells need iodine to manufacture
chemicals that are vital to the body.
Isotope

An isotope is an atom with the same
number of protons and electrons, but
different numbers of neutrons.

Isotopes with more neutrons would have a
greater mass.
Isotopes
 Atoms of the same element with
different mass numbers.
 Nuclear symbol:
Mass #
Atomic #
12
6
 Hyphen notation: carbon-12
C
Isotopes
 Chlorine-37
• atomic #:
17
• mass #:
37
• # of protons:
17
• # of electrons:
17
• # of neutrons:
20
37
17
Cl
Isotopes
Isotopes are atoms of the same element having
different masses due to varying numbers of neutrons.
Isotope
Protons
Electrons
Neutrons
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
Hydrogen-3
(tritium)
1
1
2
Nucleus
Symbols
 if
an element has an atomic
number of 34 and a mass number
of 78 what is the
–number of protons
–number of neutrons
–number of electrons
–Complete symbol
Symbols
 if
an element has 91 protons and
140 neutrons what is the
–Atomic number
–Mass number
–number of electrons
–Complete symbol
Symbols
 if
an element has 78 electrons and
117 neutrons what is the
–Atomic number
–Mass number
–number of protons
–Complete symbol
Average Atomic Mass

carbon-12 standard for average atomic mass
(perfect 12 amu)

Based on abundance of each element in nature.

Mass found on the periodic table.
Average Atomic Mass
 weighted average of all isotopes
 round to 2 decimal places
Avg.
Atomic
Mass

(mass)(% ) (mass)(% )
Average Atomic Mass
 EX: Calculate the avg. atomic mass of
oxygen if its abundance in nature is 99.76%
16O, 0.04% 17O, and 0.20% 18O.
Avg. (16)(.9976 )  (17)(.0004 )  (18)(0.002 0)

16.00
Atomic
amu
Mass
Average Atomic Mass
 EX: Find chlorine’s average atomic mass if
approximately 8 of every 10 atoms are
chlorine-35 and 2 are chlorine-37.
Avg.
Atomic 
Mass
(35)(.8)  (37)(.2)
 35.40 amu
Sample Problem - Average
Atomic Mass

Naturally occurring lead is found to have
natural percentage abundances of:
1.48% 204Pb,
23.6% 206Pb,
22.6% 207Pb,
52.3% 208Pb.

Calculate the average atomic mass of lead.
Lab Activity
How can the average atomic mass for an
element be determined given the masses
of its isotopes and their relative
abundance?
Ions
 an
atom with a charge, which means
protons are not equal to the electrons.
 positive
ions are called cations In a
positive ion, the protons are greater than
the electrons.
 negative
ions are called anions. In a
negative ion, the electrons are greater
than the protons.
Ions

To determine the charge, subtract the
electrons from the protons.

Equation: Charge = protons – electrons

The charge is shown as a superscript to
the right of the symbol.
Ions
Ex: Magnesium has 12 protons and 12 electrons in the
neutral state. (How do we know this? Answer this
question.)
If Magnesium has 12 protons, but only 10 electrons
(which is usually the case when Mg forms an ion),
is Mg more negative or more positive?
Answer: More positive because Mg now has 2 more
positive protons than negative electrons and makes
the atom positively charged.
Ion is written as....
Mg 2+
IONS
Protons
Neutrons
Electrons
Atomic #
Mass #
Name