# Presentation: 392108

## Matching the Content to Your Class

- (I was told there would be *no math*)

## Atoms and Isotopes

- What are atoms, isotopes, and radioactive decay?

## Today’s Topics

- How is energy stored in an atom?
- 	Atoms and subatomic particles
- 	Elements (Periodic Table)
- 	Isotopes (Chart of Nuclides)
- 	Nuclear forces, stability, and binding energy
- 	Radioactive decay

- Atoms and Isotopes

- The Harnessed Atom

## Atoms and Subatomic Particles

- Atoms are ***the smallest unit of a chemical element that has all the chemical properties of that element*****. **
- Made up of:
- Protons– positive charge
- Neutrons—no charge
- Electrons—negative charge

- Atoms and Isotopes

- The Harnessed Atom

## The Periodic Table of the Elements

- Atoms and Isotopes

- The Harnessed Atom

## Reading Atomic Notations

- Z is the atomic (proton) number
- N is the neutron number
- A is the mass number (N+Z)
- X is the chemical element symbol

- Atoms and Isotopes

- The Harnessed Atom

## Isotopes

- Atoms of one element may have different number of neutrons: the different possible versions of each element are called isotopes.
- Isotopes of one element all have the same number of protons (atomic number, Z) but different numbers of neutrons (thus different atomic weights, A).
- Every element has several isotopes
- All isotopes are shown on the chart of the nuclides.

- Atoms and Isotopes

- The Harnessed Atom

## Isotopes of the element sodium– 11 protons

- Isotopes of the element oxygen–
- 8 protons

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Forces

- Weak Nuclear Forces
- Particles with like charges repel.
- This causes electrons to orbit around the nucleus.

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Forces

- Strong Nuclear Forces
- Particles in the nucleus actually are held together by an even stronger attractive force.
- Acts only at very short distances (about       10-15m)—beyond this distance, the strong nuclear force is negligible.

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Forces

- Two protons more than 10-15m will repel each other by their like charges.
- Inside a nucleus, the distances are small enough that the ***strong nuclear force*** overcomes the ***weak repulsive force,*** holding the protons and neutrons together.

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Forces

- Big Idea of Science:
- There are only four
- known forces in nature:
- Gravity
- Electromagnetism
- Weak Nuclear Force
- Strong Nuclear Force

- Atoms and Isotopes

- The Harnessed Atom

## Think about it...

- How might a higher number of neutrons change the balance between the repulsive and attractive forces in a nucleus?
- How might a lower number of neutrons affect this same balance?

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Stability

- The stability of an atom is the balance of the repulsive and attractive forces within the nucleus (strong and weak force in equilibrium).

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Stability

- If the attractive strong forces prevail, the nucleus is stable.
- If the repulsive weak forces outweigh the attraction of the strong forces, the nucleus is unstable.

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Stability

- For elements with low atomic numbers, atoms are stable when their neutron to proton ratio is close to one (1:1).
- As atomic number increases, stable atoms have ratios greater than one (1:1.5).
- This is because at higher atomic numbers, more neutrons are needed to counteract the repulsive forces between the protons.

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Stability

**Nuclear Stability**

**The shaded cluster is the “band of stability.” **
**The solid line represents a neutron-to-proton ratio of 1:1. **
**Nuclei to the right of the band of stability don’t have enough neutrons to remain stable.**
**Nuclei to the left of the band have too many neutrons to remain stable.**

- Atoms and Isotopes

- The Harnessed Atom

## Nuclear Binding Energy

- The energy stored in the bonds within an atom
- Released when an atom breaks apart
- Represented by the equation:
***E******b***** (MeV) = (*****Zm******p***** + *****Nm******n***** – M****A****) x 931.494 MeV/amu**
*	**Where:*
*1 amu* = 1.66 x 10-24 grams *[amu = atomic mass unit]*
*E**b**= binding energy*
*Zm= mass of the protons in amu*
*Nm= mass of neutrons*
- MA= *mass of the atom*
- MeV= millions of electron volts, a unit of measure used to represent the energy in nuclear equations

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

- Unstable atoms will spontaneously transform until they reach a stable configuration.
- These transformations are accompanied by releases of energy.

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

- This energy, given off in waves from an atom, is known as ***radiation***.
- Substances that give off radiation are called ***radioactive.***
- The process of isotopes emitting particles and energy to become more stable is called ***radioactive decay***.

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

- Main types of radioactive decay:
- Alpha emission
- Beta emission
- Positron emission
- Gamma emission

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

**Alpha emission (****α****)**
- Nucleus emits an alpha particle—two protons and two neutrons
- Equivalent to a helium nucleus (He).
- Alpha Decay Animation _[http://ie.lbl.gov/education/glossary/AnimatedDecays/AlphaDecay.html](http://ie.lbl.gov/education/glossary/AnimatedDecays/AlphaDecay.html)_

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

**Beta Emission (****β****)**
- Nucleus emits an electron, and a neutron is converted to a proton.
- Beta Decay Animations: _[http://ie.lbl.gov/education/glossary/AnimatedDecays/Beta-Decay.html](http://ie.lbl.gov/education/glossary/AnimatedDecays/Beta-Decay.html)_

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

**Positron Emission**
- Nucleus emits a positron (identical to an electron in mass, but has a positive charge)
- Positron is formed when a proton converts to a neutron.

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay

**Gamma emission (****γ****)**
- Nuclei seeking lower energy states emit electromagnetic radiation, which is in the gamma ray region of the electromagnetic spectrum.
- Rays are emitted in conjunction with another type of decay (alpha or beta).
- Gamma Decay _[http://ie.lbl.gov/education/glossary/AnimatedDecays/GammaDecay.html](http://ie.lbl.gov/education/glossary/AnimatedDecays/GammaDecay.html)_
- Additional animations: _[http://](http://ie.lbl.gov/education/glossary/Glossary.htm)__[ie.lbl.gov/education/glossary/Glossary.htm](http://ie.lbl.gov/education/glossary/Glossary.htm)_

- Atoms and Isotopes

- The Harnessed Atom

## Radioactive Decay Chains

- Atoms and Isotopes

- The Harnessed Atom

## Half Life

- The amount of time it takes for half of the atoms of a given isotope to decay to another form is known as its half-life.
- The value can be from fractions of a second to billions of years.

- Atoms and Isotopes

- The Harnessed Atom

## Half Life

- Half-life values are constant.
- There is no way to speed up or slow down this natural process.
***Cannot*** predict when a specific atom will decay.
***Can*** predict the number of atoms that will decay in a certain time period.

- Atoms and Isotopes

- The Harnessed Atom

## Half Life of Uranium-235

- Atoms and Isotopes

- The Harnessed Atom

## Words to Know...

- Alpha decay
- Atom
- Beta decay
- Chart of Nuclides
- Coulomb’s force
- Electron
- Electron capture
- Element
- Gamma decay
- Half-Life
- Isotope

- Neutron
- Nuclear force
- Nucleus
- Nuclide
- Periodic Table
- Positron
- Proton
- Radiation
- Radioactive Decay
- Stability

- Atoms and Isotopes

- The Harnessed Atom

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