Catalyst• 1. Write down Dalton’s postulate that was proven

wrong by the existence of isotopes.• 2. How does the existence of isotopes disprove this

component of Dalton’s atomic theory?

End

Marie Curie!• Marie Klodowska Curie discovered the mysterious

element radium. It opened the door to deep changes in the way scientists think about matter and energy.

• Radioactivity had nothing to do with whether the material was solid or powdered, dry or wet, pure or combined with other chemical elements. If you had a certain amount of uranium—a certain number of uranium atoms—then you got a certain intensity of radiation. Nothing else made a difference.

Women in STEM• When the Nobel Prize for Physics was awarded to Pierre and Marie

Curie in 1903, the great honor quickly changed their lives. Pierre was finally appointed to a professorship at the Sorbonne, and the university belatedly found funds for a laboratory for him. It also hired Marie—the first woman to win a Nobel Prize—as “laboratory chief.”

Module 2.3 – Marie Curied Boar Meat

Next Model in the Development of Atomic Theory: Curie

ISOTOPES AND RADIOACTIVE DECAY

Today’s Learning Targets• LT 2.3 – I can identify the number of protons as the

atomic number and calculate average atomic mass on the periodic table using relative isotope abundance data.

What are isotopes?

I. Isotopes• Isotope – Atoms of the same element have

different numbers of neutrons and thus have different atomic masses.

How are isotopes and relative abundances related?

II. Calculating Average Atomic Mass

• In nature, we have various amounts of each isotope of an element

• Therefore, we use the abundance to get a relative mass

Class Example

• Naturally occurring chlorine is 75.78% 35Cl and 24.22% 37Cl. Calculate the average atomic mass of chlorine.

Table Talk

• Three isotopes of silicon occur in nature, 92.23% is 28Si, 4.68% is 29Si, and 3.09% is 30Si. Calculate the average atomic mass of silicon.

Stop and Jot

• Only two isotopes of copper occur naturally 63Cu accounts for 69.17% and 30.83% is 65Cu. Calculate the average atomic mass of copper.

Summarize!

Use the following terms in your summary:• Isotope• Relative Abundance• Sum

Learning Target Log Assessment

• Go to letsgeddit and rate your current level of understanding for LT 2.2. Rate yourself 1 – 4.

How does this connect to radioactive boars?

Radioactive Boar Meat!• Make some radioactive boar burgers!• Good idea? Or nah?

Online Simulator• Please open the two simulators on the computer

and complete the simulator handout with a partner.

What is radioactive decay?

I. Radioactive Decay• Atoms can be unstable and breakdown• Radioactive Decay – The spontaneous breakdown

of the nucleus into a smaller nucleus, accompanied by the release of particles, radiation, or both.

What are the three types of decay?

I. Alpha (α) Decay• Alpha Decay – When an atom splits its nucleus into:

1. A smaller nucleus and 2. A Helium atom (2 protons, 2 neutrons).

• Observed often in very heavy atoms• Alpha particles on travel a few cm in air• Paper blocks alpha particles

Alpha Radiation

II. Beta (β) Decay• Some elements are unstable because their proton to

neutron ratio is too large.• Beta decay converts neutrons to protons and

releases an electron known as a beta particleneutron proton + β

• Travel a few meters in the air• Metals provide a shield against beta radiation.

Electron

Beta Radiation

III. Gamma (γ) Decay• Gamma rays are high energy waves that are

released when nucleus goes from high energy state to low energy.

• Gamma radiation is the most dangerous. It can lead to DNA mutations and cancers.

• Gamma radiation requires thick pieces of lead/concrete in order to stop.

Gamma Radiation

Radiation SummaryType of Radiation Description Blocked by?

Alpha (α)

Beta (β)

Gamma (γ)

The spitting of a nucleus into a smaller nucleus and a He atom (alpha particle

Converts a neutron to a proton and an electron

(beta particle)

High energy waves that are released by nucleus

Blocked by paper

Blocked by metals

Blocked by lead

Class Example

• Label the following decay as alpha, beta or gamma decay

4319K 43

20Ca + electron

Table Talk• Label the following decay as alpha, beta or

gamma decay210

84Po 20682Pb + 4

2He

Table Talk

• Complete the following reaction if it undergoes beta decay:

147N ______ + _______

SUMMARIZE!Use the following terms in your summary:• Alpha• Beta• Gamma• Decay• Radioactive

Work Time• Work on practice for the next 10 minutes.

Learning Target Log Assessment

• Rate your current level of understanding of LT Rate yourself 1 – 4.

Exit Slip

1. Naturally occurring chlorine is 75.78% 35Cl and 24.22% 37Cl. Calculate the average atomic mass of chlorine.

2. What is gamma decay? What will stop gamma radiation?

3. What type of decay is shown below: 231

91Pa 22789Ac + 4

2He

Learning Target Log Assessment

• Rate your current level of understanding of LT. Rate yourself 1 – 4.

Closing Time• Practice due Monday/Tuesday• Test next Tuesday/Wednesday