Discrete Energy and Radioactivity

Unit 7.1

Disclaimer:

• “We return to this for HL students in Topic 12, but for now it is maybe better to accept that is how nature operates.”

Chemistry Review

• Atom – protons, neutrons and electrons– Number of protons determines the element– More or less neutrons = isotope– More or less electrons = ion (+ or – charge)

Nuclide Notation

Isotopes

• Number of protons is always the same!

Where are the electrons?

• Can be located in different energy levels

Movement Between Levels

• When excited electrons move faster and are in a higher energy level.

• Ground State – standard level of energy of an electron– n = 1

Moving Levels

• To move energy levels electrons must be given an exact amount of energy

• Hydrogen:

Practice

• Calculate the energy needed for an electron to move energy levels in lithium:

Photons

• Photons – light energy absorbed or emitted– Energy carried based on frequency– Like a “zap” of energy

Remember This?

Wavelength and Frequency

• We can find the wavelength and frequency of photons absorbed or emitted:

Equations

• We can use previous equations to derive wavelength of the photon:

Lyman Series

Balmer Series

Pashen Series

Emission/absorption Spectrum of Hydrogen

Emission Spectra

• Spectrometer – used to pass a voltage through a gas to show emission

• Hydrogen:– Lyman Series – ultraviolet and n=1– Balmer Series – visible light and n=2– Pashen Series – Infrared and n=3

Absorption Spectra• Light is passed through solid, liquid or dense

gas and light shows through while dark lines are formed at the same point of the emission spectrum– Every element has a unique spectra, like it’s own

fingerprint

Radioactive Decay

• Naturally occurring process in which the nucleus of an unstable atom will spontaneously change into a different nuclear configuration by the emission of alpha or beta particles and gamma radiation

• Overview Video

Unstable Nuclei• An unstable nuclei emits a particle to become

more stable, this is decay• The decay of an unstable nucleus is random.

We know it’s going to happen, but we can’t say when! It is spontaneous. It cannot be affected by temperature/pressure etc.

4 Types of Decay

• Alpha Decay• Negative Beta Decay• Positron Beta Decay• Gamma Radiation

Alpha Decay (α)

• An unstable nuclide emits a particle of the same configuration as helium

Negative Beta Decay (β¯)

• An unstable nuclide emits an electron and a neutron is converted to a proton

• Also emits an antineutrino (don’t ask, just accept it for now)

Negative Beta Decay (β¯)

• Example:

Positron Beta Decay (β+)

• An unstable nuclide emits a positron and a proton is converted to a neutron– Positron = antiparticle of an electron

• Also emits a neutrino (Again, don’t ask, just accept that is how nature operates)

Positron Beta Decay (β+)

• Example:

Gamma Ray Emission (ϒ)

• Gamma rays are high-energy photons and accompanies other decay mechanisms

• Daughter nucleus is left in an excited state, gamma rays “release” the extra energy to make the electrons less excited

Gamma Ray Emission (ϒ)

• Example:

Radioactive Decay

Overall what you need to know:

Half-Life

• Because your lives are not horrible enough…

Excel Spreadsheet for modeling!!