Isotopes, Stability, and Radioactivity

How can you tell if an isotope is stable or

not?

Objectives

To predict if an isotope will be radioactive or not based on the ratio of Neutrons:ProtonsUsing a Stability Chart

To compare and contrast:Ionizing radiationNon-ionizing radiation

VocabularyNuclear Chemistry: the study of the

nucleus, and the effect if we change the number of protons and/or neutrons

Radioactivity: Happens when unstable isotopes give off atomic sub-particles and energy in order to become more stable.What are atomic sub-particles given off?Protons & Neutrons

How do we know if an isotope is radioactive?

Protons and Neutrons are in the nucleus. Protons are positively charged and should repel each other.

The nuclear force is the force that holds the nucleus together. The nuclear force is stabilized by having an appropriate number of neutrons to stop the protons from repelling each other.

When the amount of neutrons is too high or low, the nucleus becomes unstable.

Radioactive isotopes will give off protons, neutrons, and or energy until the nucleus becomes stable.

Look at its’ atomic number and calculate the ratio of neutrons:protons.

This is a rough estimate if you are not given a Stability chart.

What is stable?Atomic # 1-20 AND neutrons: protons is 1:1 Atomic # 21-83 AND neutrons:protons is 1.5 : 1

Any isotope outside of this ratio (big or small) is radioactive.

All atoms with more than 83 protons (bismuth) are radioactive no matter the ratio.

How do we know if an atom is radioactive?

Examples:1. Is Polonium-212 stable?

No, it has an atomic number greater than 832. Is potassium-42 stable?

# neutrons: 42-19 = 23# protons: 19#neutrons:protons = 23/19 =1.2 : 1For an atomic # >20, it should be 1.0 Therefore, no it is not stable.

2. Is calcium 40 stable?# neutrons: 40-20 = 20# protons: 20#neutrons:protons = 20/20 = 1.0 : 1For an atomic # >20, it should be 1.0 Therefore, yes it is stable.

Stability ChartMost accurate way to

determine if an isotope is stable or not.

Look up based on number of protons and neutrons.

If the isotope is on the band, it is stable.

If it sits on top of the band, it has too many neutrons

If it is under the band, it has too many protons

Atomic # >83 has too many neutrons & protons

Too Many Neutrons

Too Many Protons & Neutrons

Too Many Protons

Examples:1. Is Carbon-14 stable?# neutrons: 14-6=8# protons: 6No.2. Is Calcium-40 stable?# neutrons: 40-20=20#protons: 20Yes3. Is zinc-60 stable?# neutrons: 60-30=30# protons: 30No.

RadiationRadiation — the energy given off from a source

in the form of waveswaves or particles and can travel great a distance.Think about the ripples of water that radiate

outwards in a pond after a pebble is dropped into the water

Examples of sources : Light bulbsThe sunA radioA microwave

There are many different types of radiation

Main Types of Radiation

Non-ionizing Radiation – has lower levels of energy

The energy is so low, that it is not strong enough to affect the atoms it comes in contact with. Examples: visible light, radiowaves, microwaves, infrared

rays from a heat lampIonizing Radiation – has higher levels of energyThis high energy radiation will affect the atoms it

comes in contact with, including human tissue which it will pass through.Examples: x-rays, gamma rays