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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)

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matching the content to your class

Matching the Content to Your Class

(I was told there would be no math)

atoms and isotopes

Atoms and Isotopes

What are atoms, isotopes, and radioactive decay?

today s topics
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

atoms and subatomic particles
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

reading atomic notations
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

  • 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


Isotopes of the element sodium– 11 protons

Isotopes of the element oxygen–

8 protons

Atoms and Isotopes

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

Atoms and Isotopes

nuclear forces10
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

nuclear forces11
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

nuclear forces12
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

think about it
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

nuclear stability
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

nuclear stability15
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

nuclear stability16
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

nuclear stability17
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


Nuclear Binding Energy

  • The energy stored in the bonds within an atom
  • Released when an atom breaks apart
  • Represented by the equation:

Eb (MeV) = (Zmp + Nmn – MA) x 931.494 MeV/amu


      • 1 amu = 1.66 x 10-24 grams [amu = atomic mass unit]
      • Eb= 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

radioactive decay
Radioactive Decay
  • Unstable atoms will spontaneously transform until they reach a stable configuration.
  • These transformations are accompanied by releases of energy.

Atoms and Isotopes

radioactive decay20
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

radioactive decay21
Radioactive Decay
  • Main types of radioactive decay:
    • Alpha emission
    • Beta emission
    • Positron emission
    • Gamma emission

Atoms and Isotopes

radioactive decay22
Radioactive Decay

Alpha emission (α)

  • Nucleus emits an alpha particle—two protons and two neutrons
  • Equivalent to a helium nucleus (He).

Alpha Decay Animation

Atoms and Isotopes

radioactive decay23
Radioactive Decay

Beta Emission (β)

  • Nucleus emits an electron, and a neutron is converted to a proton.

Beta Decay Animations:

Atoms and Isotopes

radioactive decay24
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

radioactive decay25
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

Additional animations:

Radioactive Decay

Atoms and Isotopes

radioactive decay chains
Radioactive Decay Chains

Atoms and Isotopes

half life
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

half life28
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

half life of uranium 235
Half Life of Uranium-235

Atoms and Isotopes

words to know
Alpha decay


Beta decay

Chart of Nuclides

Coulomb’s force


Electron capture


Gamma decay




Nuclear force



Periodic Table




Radioactive Decay


Words to Know…

Atoms and Isotopes


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