3.(a) Periodic Table, Isotope abundance

chapter 3

(b) Origin of Food

A group of elements consists of all the elements in any vertical column of periodic table.

The elements in each horizontal row of the periodic table represent a period.

The Periodic Table(see www.webelements.com)

Isolation of Elements

• He from natural gas-looming shortage (escapes from the atmosphere)

• Ne, Ar, Kr, Xe come from fractional distillation of liquid air

• Radon (Ra) comes from radioactive decay of radium

• Halogens found as ions in sea salt, ie NaCl, KI etc.

Evaporation of Sea water

• New Zealand Salt beds, sources of Cl, Br , I in salts

The atomic weight of an element is the

average of the mass of all of its isotopes, weighted for the abundance of each.

If the atomic weight of Cl = 35.5 and Cl has two isotopes :

Cl Cl1717

35 37

Approximately how much of each isotope occurs in natural abundance?

Tough Question!

• Where to start?• Any suggestions?• If 50% of each isotope, • atomic weight would be?

Isotopes of Chlorine

• Let fraction of 35Cl=x, thus fraction of 37Cl=1-x

• So x(35) + (1-x)37= 35.5• 35x +37 -37x = 35.5• -2x= -1.5• x=.75

Thus about 75 % 35Cl and 25 % 37Cl.

Life’s Good things Come from Chemistry!

C H O Co La Te

Food: The Macronutrients

• Carbohydrates (4 calories/gram)

• Protein (4 calories /gram)

• Fats (9 calories/ gram)

• >99% of calories come from these

• -------------------------------------------------

• Micronutrients; Essential, but in much smaller amounts: Vitamins, Minerals

Where does our food come from?

.. .. . .

-+.

Origin of Carbohydrates: Photosynthesis

• 6CO2 + 6H2O C6H12O6 +6 O2

• Glucose (a sugar) is formed

• Reaction catalyzed by chlorophyll and requires sunlight

• Balanced Equation: equal # of C, H, O on LHS and RHS

Biosynthesis of Carbohydrates

• Plants convert glucose to more complex sugars ie. cellulose, starch

• Plants “fix” nitrogen from soil and air (78% N2, 20% O2, all others 2%)

• Animals convert plants to protein and fats

Biosynthesis of Fatty Acids

• Complex: involve enzymes (catalysts) , ie Acetyl Coenzyme A.

• Fats are biosynthesized by sequential addition of 2C units.

• Palmitic acid –a C16 saturated fatty acid requires 8 Acetyl Co A units

• Plants make these in their seed

Biosynthesis of Fats in Plants

Rapeseed (Canola) : source of a “healthy mixture of unsaturated fatty acids

Biosynthesis of Protein

• From amino acids

• Human body can biosynthesize some proteins (for muscle, hair, hormones)