Atoms and Isotopesthe 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

What is Radioactivity?

Slide 7

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

Periodic Table

Slide 9

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.

Uranium 238 decay

The half life of U-238 is

4.5 billion years.

Slide 11

If you start with 100 g of U-238

4.5 billion years later you have

50 g of U-238

(half of parent left)

50 g of Pb-82

(new daughter element)