Download - Atoms and Isotopes the light bulb is a reminder you need to do something on your notes page
What are isotopes? Atoms of an element that have different masses
This occurs by changing the number of neutrons in the nucleus.
Carbon-12
atomic mass = 12 AMU
6 p+ and 6 n = 12 AMU
Why are all these atoms still called CARBON?
Slide 1
Key
AMU = atomic mass unit
Carbon-13
atomic mass = 13 AMU
6 p+ and 7 n = 13 AMU
Carbon-14
atomic mass = 14 AMU
6 p+ and 8 n = 14 AMU
What are isotopes?Isotopes of Hydrogen
Key
AMU = atomic mass unitHydrogen-1
atomic mass = 1 AMU
1 p+ and 0 n = 1 AMU
Hydrogen-2 (deuterium)
atomic mass = 2 AMU
1 p+ and 1 n = 2 AMU
Hydrogen-3 (tritium)
atomic mass = 3 AMU
1 p+ and 2 n = 3 AMU
H11
H1
2
H1
3
Hydrogen is the only element that has different names for its isotopes
Slide 2
Standard atomic
notation
Mass number on top
Atomic number on bottom
Periodic Table Notation
Isotopes are written using standard atomic notation. Potassium has three isotopes,
Potassium is found in nature in a certain ratio of isotopes. 93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41 Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1 AMU
1939 K, 19
40 K, 1941K
AMU = atomic mass unit
So why is the mass of K listed as 39.1 AMU?
Slide 3
What is Radioactivity?Elements that are RADIOACTIVE have nuclei that are UNSTABLE.
Why is this nucleus unstable?
Count up the number of protons and neutrons – are there more attractive or repulsive forces in this nucleus?
Slide 4
A nucleus is unstable if it has
too many particles in the nucleus.
To become STABLE, they give up
particles or energy and this is…….
Radioactivity
What is Radioactivity?
The strong nuclear force holds the protons and neutrons together but when the repulsive force of the protons gets too large then the atom undergoes radioactive decay.
Slide 5
Radioactive Decay
Parent nucleus
(unstable)Daughter nucleus
Radioactivity released
The radioactivity released can be
particles or energy
Slide 6
Radioactivity• All elements have at least one radioactive isotope.• All isotopes with atomic number greater than 83
are radioactive.
Graph of Stable and Unstable isotopes
Example: Uranium-238
Proton number = 92
Neutrons = 146
Slide 8
Uranium 238 decay (U-238)
Slide 10
Unstable parent nucleus
First decay product
Stable daughter
nucleus
Q: Why is the mass of the daughter nucleus
less than the mass of the parent nucleus?
A: The daughter nucleus has LOST neutrons
to become stable.
Q: Why is the atomic number of the daughter
nucleus less than the atomic number of the
parent nucleus?
A: The daughter nucleus has LOST protons
to become stable and has
become a different element.