Isotopes and Radioactivity

OUTCOME QUESTION(S): C12-2-04 ENERGY AND ATOMIC MODELS Explain average atomic mass using isotopes and their relative abundance. Include: radioisotopes Describe the electromagnetic spectrum in terms of frequency, wavelength, and energy. Include: Plank’s Equation, quantum, photon Understand the historical development of the Quantum Mechanical Model of the atom. Describe how unique line spectra are created for each element. Include: Bohr model Vocabulary & Concepts Radioisotope Radioactive decay Half-life

BUT atoms can gain or lose electrons forming IONS +1 +3 -3 -2 -1 +2 +4/-4 We use the proton number (atomic number) to identify elements since protons are not gained or lost

The atomic number (Z) is the number of protons in the nucleus of an atom - identifies an element. The atomic mass (A) is the number of protons plus the number of neutrons. There are many element notations – just remember the mass is always the bigger number

Isotopes: Atoms with the but a different number of neutrons. same number of protons Hydrogen Atomic Mass = 1 Atomic Number = 1 RA: 99.985% Deuterium Atomic Mass = 2 Atomic Number = 1 RA: 0.015% Relative Abundance (RA): Percentage of that isotope that would appear in an average sample. Atomic mass on the Periodic Table is actually an average of isotopes of an element based on relative abundance in nature

Isotopes are VERY common

Mass spectrometer determines the mass of individual atoms or isotopes. Sends atoms through a magnetic field which bends their paths. The heavier the atom – the less it bends

1. 19 protons and 20 neutrons - mass number of 39 Potassium isotopes: 1. 19 protons and 20 neutrons - mass number of 39 (potassium-39 39K RA: 93.26%) 2. 19 protons and 21 neutrons - mass number of 40 (potassium-40 40K RA: 0.012%) 3. 19 protons and 22 neutrons - mass number of 41 (potassium-41 41K RA: 6.730%) Notice how the atomic mass (A) is used in the notation to show which isotope is being referred too

Convert the RA percent to a decimal Magnesium exists as three isotopes in the world: 78.99% is 24Mg (23.985 μ) 10.00% is 25Mg (24.986 μ) 11.01% is 26Mg (25.982 μ) Convert the RA percent to a decimal Calculate the average atomic mass of magnesium: (0.7899)(23.985 μ) = 18.95 μ + (0.1000)(24.986 μ) = 2.499 μ = 24.31 μ (0.1101)(25.982 μ) = 2.861 μ Sum the results

Rubidium has two common isotopes, 85Rb and 87Rb Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass? 72.2% is 85Rb (85 μ) 27.8% is 87Rb (87 μ) + (0.722)(85 μ) = 61.37 μ = 85.56 μ (0.278)(87 μ) = 24.19 μ

helium 5He 6He The nucleus of many isotopes are unstable and break apart over time - radioactivity.

Radioisotopes - unstable nuclei releasing energy and/or particles. Release of energy is called radioactive decay. Half-life - amount of time it takes for half the radioisotope to be converted into another particle. Atoms may be converted into another isotope of the same element or a completely different element

Many different types of decay exist: alpha decay, beta decay, gamma decay…

Notice many different types of decay take place. This is called a decay chain – it shows the products of the radioactive decay of an element. Notice many different types of decay take place. This is like real alchemy…

C12-2-04 ENERGY AND ATOMIC MODELS CAN YOU / HAVE YOU? C12-2-04 ENERGY AND ATOMIC MODELS Explain average atomic mass using isotopes and their relative abundance. Include: radioisotopes Describe the electromagnetic spectrum in terms of frequency, wavelength, and energy. Include: Plank’s Equation, quantum, photon Understand the historical development of the Quantum Mechanical Model of the atom. Describe how unique line spectra are created for each element. Include: Bohr model Vocabulary & Concepts Radioisotope Radioactive decay Half-life