Chemical bonds (Ionic)

Radioisotopes

Thursday, June 11, 15

- can be stopped by a brick of lead

Radioisotopes✦ Radioisotopes - have an unstable nucleus and emit subatomic particles or energy as they decay into more stable atoms

alpha particles (α)

beta particles (β)

gamma rays (γ)

- a helium nucleus - can be stopped by a sheet of paper

What can stop them?

- high speed electrons- can be stopped by a sheet of lead- energetic electromagnetic radiation

α- paper sheet

β- lead sheet

γ- lead brick

✦ Radioactive emissions include:

Thursday, June 11, 15

C14

6

20Ca

45

19K

40

53I

131

88Ra

226

Radioisotope Uses

Trace movement of carbon through biological pathways, like respiration and photosynthesis

Measures rate of bone formation

Half-life of 1.3 billion years (decays into 40Ar)Ratio of 40K : 40Ar used to date fossils

Taken up by thyroid glandGland can be imaged to detect abnormalities

Emits radiation that can destroy living cellsUsed to treat cancer tumors

Radioisotopes

Figure 1: Scientific and medical uses for some radioisotopes

Thursday, June 11, 15

Radiation can damage cells

Extremely useful in diagnosis and treatment of diseases

Example 1: inject radioactive material into patient and trace its movement in the body

Example 2: energy emitted from radioactive decay can be directed to a tumour

Short half-life preferred 

Radioisotopes in Medicine

Thursday, June 11, 15

Tracer - radioisotope placed in body on biologically active molecule (glucose, water, or ammonia)

Give off gamma rays as they decay - easily detectable

How are TheyTraced?

PET scan of 47 y/o woman, shows leukemia present in bone marrow before treatment (left) and after chemotherapy (right)

Thursday, June 11, 15

Ionic Bonds

Covalent Bonds

Polar Covalent Bonds

Chemical Bonds

✦ Chemical bonds are formed between atoms by interaction of their respective electrons

✦Three types of intramolecular bonds (bonds that hold atoms in a molecule together):

Thursday, June 11, 15

Ionic Bonds

11p+

12no17p+

18no

Na+ Cl-

-

Electrostatic attraction

cation anion

✦ Ionic Bond - occurs when there is a transfer of one or more electrons from one atom to another

✦ Transfer leads to formation of a cation and anion ✦Resulting electrostatic attraction between these two oppositely charged ions is an ionic bond

+

Thursday, June 11, 15