Human Chemistry


Reading - Chapter 2

•Need to learn this material for rest of course

- Less interested testing than in your learning it

- importance will become apparent soon when you can apply the info.

•Begin to apply it next week --> behoove you to learn this information very well.

•Emphasize the importance of these chemicals to the human body



A few terms:

Matter - what all living things consist of

- anything that occupies space and has mass.

- solid, liquid, gas

(Mass refers to the amount of matter in an object)


energy - capacity to do work (ex. - move mass)

- chemical - Energy released or absorbedw/chemical bond formed/broken

- radiant - light

- electrical - flow of electrons

- heat - differnece in temp can be transferred (ice cubes)

- mechanical - position or movement of mass


Matter - composed of:

elements - chemical substances that cannot be broken down into simpler substances by ordinary chemical means.



• Elements - represented by either 1 or 2 letter symbols

ie - H = hydrogen, O = oxygen, and Na = sodium

• Currently recognize 109 dif elements, 96 occur naturally.

New elements are still being created in laboratories.


• About 26 elements are found in living organisms

         4 of them C, H, O, N acct for 96% of the bodys weight

         O - 65%, C - 20%, H - 10%, N - 3%


Elements - made up of units of matter called


•mostly space

•consists of two parts:

1) nucleus - •positively charged protons, •uncharged neutrons.

2) electrons - negatively charged particles, move around nucleus in a cloud

• # of electrons = # of protons

• since:        protons - positive

                          electrons - negative ---> the atom is neutrally charged.


Q: If all atoms (except H) are composed of protons, neutrons and electrons then how do we acct for their dif chemical properties?

1) # of parts

2) # electrons in outer shell (more on this later - Chemical Reactions)


•# of protons critical:

- the atomic number of an element is the number of protons in its atoms.

e.g. -       1 proton --> H

              8 --> O

(Another measure is atomic weight,= the number of protons and neutrons)


Some elements of dif #'s of neutrons-


1) all atoms of the same element - same # of protons

2) Some - dif #s of neutrons --> dif atomic weights

3) But have same chemical properties


•Some elements- >dozen dif isotopes

• others - as few as 2

Ex - C - 99% have 6 p/6 n ;

1% - 11C - 5 neutrons

      others have 7 or 8 ns - most have 6 ---> atomic weight of 12


Why talk about isotopes?

Because they have direct relevance to issues of human health


In particular:

•Some isotopes are naturally radioactive and others can be made radioactive by bombarding them with neutrons and protons in the lab.

•An element is considered radioactive when its nucleus undergoes spontaneous changes to a more stable configuration.

•radioactive decay --> nuclear particles and radiation both emitted

---> can be measured

•Many of these radioisotopes are used in medicine and biology.

One example of this type of technology which was recently been developed is the


EX - 1 - Positron Emission Tomography (PET) scan.

•Short-lived radioisotopes such as 11C, 13 N or 15O

--> produced and incorporated into a solution

--> injected into circulatory system.

isotopes circulate through the body

--> decay and emit positrons

--> positrons collide with electrons in the body

--> release gamma rays

--> measured by detectors.

computer analyzes the info

--> constructs a PET scan

--> shows where the isotopes are being used in the body.


provides unique information

(CT scan or MRI do not).

provides some idea of the functioning of organs.



•the effects of of drugs in body organs

measure blood flow through blood vessels in the brain and the heart

•diagnose coronary heart disease

•identify the extent of stroke,

•and to detect cancers


And this is only one of the many uses of radioisotopes

EX - 2 - Radiation treatment

Other isotopes (Cobalt, Phosphorus, Sodium) can be injected into cancer patients

--> kill the cancer cells.


2) Chemical Rx:Foundation for all Life processes

TO understand need to know:

Electron Shells

• electrons around nucleus distributed in layers called shells.

• Seven of these shells are known to exist

- inner shell - 2

- next two outermost shells - usually 8

• stability - atoms empty/fill outermost --->

1) give; 2) share; 3) accept electrons

• Reactivity - detd by # of electrons in outer shell

         --> these take part in chemical reactions.

Stable atoms - atom has maximum # of electrons in the outer shell

EX - (He, Ne, Ar)

Reactive atoms - atoms with incomplete outer shells - tend to gain or lose electrons

         --> this is how chemical reactions occur.


EX 1: Sodium atoms - 2 in first, 8 in second 1 in third - tends to lose its electron.

EX 2: Oxygen has 2 in first, 6 in outer --> tends to gain 2 electrons.

EX 3: Hydrogen 1 in outer --> tends to give it up.


Q: How many H atoms would it take to fill the needs of an O atom?

Right ---> now talking about more than one atom we are talking about



•Atoms - usually combined in nature --> molecules

ie.- water (H2O) or carbon dioxide (CO2)

•When atoms interact chemically --> molecules

atoms held together by chemical bonds.


3 primary types of chemical bonds:


1) Covalent - sharing of electrons (versus giving 1 up) between two atoms

• very common in body


- always shared in pairs

- bonds are very stable.

• EX - H2O, proteins, fats and carbos.