CHEMISTRY REVIEW •List the six major elements found in the human body.

–Carbon – 19.37%–Hydrogen – 9.31%–Nitrogen – 5.14%–Oxygen – 62.81%–Phosphorus – 0.63%–Sulfur – 0.64%

Remember an element is a substance that can not be broken down into simpler substances by ordinary chemical means

The smallest part of an element that retains the elements properties is an

atom.Standard atomic notation

M = mass number

(protons + neutrons) E = element

A = atomic number

[number of protons (p+) in an atom]

Determines the identity of an atom!NOTE: Mass number – atomic number = number of neutrons (n0)

Atomic StructureOrbitals/shells contain electrons (e-) which determine the chemical reactivity of an element!

Nucleus contains protons and neutrons

(p+) (n0)

Try this…

http://www.kscience.co.uk/animations/atom.htm

Ions: changing the number of electrons in an atom (mass and atomic

number remain unchanged)• An atom that carries an electrical charge

is called an ion • If the atom loses electrons, the atom

becomes positively charged (because the number of positively charged protons will be more than the number of electrons) This positively charged ion is called a cation.

Ions continued

• If an atom gains electrons, the atom becomes negatively charged (more negative charges than positive charges)This is called an anion

Ions in biological systems

• H+ (hydrogen ions) are critical to the process of cellular respiration.

• Na+ are part of transport mechanisms that enable other molecules to enter cells

• Na+ and K+ are critical to nerve impulses• Ca2+ is critical to neurotransmitter release

or muscle functioning.

Isotopes

• Atoms with the same atomic number (p+) but different atomic masses.

• Thus they contain a different number of neutrons but the same number of protons and electrons.

(p+) (e-) (no)12

6C 6 p+ 6e- 6n0 Carbon - 12

136C 6 p+ 6 e- 7 n0 Carbon -

13

146C 6 p+ 6 e- 8 n0 Carbon –

14Unstable &radioactive

Isotopes

Half-life

• Time it takes for half of the radioactive nuclei to decay in a radioisotope.

Useful Applications of Radioisotopes

1. RADIOMETRIC DATING: radioactive isotopes decay at a predictable rate

– Living organisms have the same amount of C-12 and C-14 as in the atmosphere.

– When an organism dies C-14 starts decaying to C-12 at a constant rate.

– Scientists measure the ratio of C-12:C-14 in dead fossilized organisms to predict time of death.

Carbon dating

Useful Applications Radioisotopes continued

2. Radioactive Tracers: Radioisotopes are used to follow chemicals through chemical reactions and trace their path as they move through cells/bodies of living organisms.This has applications in biological, chemical, and medical research.

Example 1: Thyroid Gland

• The thyroid gland uses iodine to make hormones that influence growth and metabolism.– Doctors administer radioactive iodine-

131, and then use a photographic device to trace the radiation

Example 2: Using positron emission tomography (PET) to diagnose

cancer tumours• Cancerous tissues are characterized by a much

higher level of activity than healthy tissues.• Thus cancer cells take in more glucose – a

common cellular energy source – than healthy cells.

• If a patient is injected with radioactive glucose and then a PET scan can be done to determine the location of a cancerous tumour.

Questions to consider

1. What radionuclide tends to be used for PET scans in place of glucose?

2. What happens to glucose when it is taken up by a cell? What happens to the modified molecule that is taken up by the cells?

3. What is a positron?4. What other imaging techniques are often

used with PET scans?5. What is the generalized half life of the

radionuclides used in PET scans? Explain.

Assignment

• Answer questions #16 on page 10 of your textbook.