General ---------Biology ------------------Online---------------------wilcox@sunline.net Ch.  2 :  The Chemical Context of Life

Hydrogen is the smallest atom:  1 proton, 0 neutrons, 1 electron.
The atomic number (of protons) of H is ____?
The atomic weight (mass of protons + neutrons) of H is also ____?
The first electron shell or "orbital" can hold up to 2 electrons, then it is full.
Atoms appear "driven" to fill their outer electron shell.  It is this tendency that explains how atoms "react" to form molecules.

Since an electron scribes a slightly different orbit each time it circles the nucleus, a better way to draw an electron orbiting is as a spherical cloud of negative charge, click here.

Fig. 2.5 and 2.8 in your text, on page 25 & 27, represent electrons as blue orbits, some spherical and some with figure eight shapes.

If an orbiting electron is given more energy, say by a ray of sunlight, it will use this energy to move to a higher orbit, further away from the + nucleus.  If the high energy electron begins to loose energy, it will fall all the way back to its original orbit, and it will give off all the extra energy it absorbed from the sunlight.  This energy given off can leave the atom as some form of radiation or light, as heat or as other forms of energy the cell can use.  Understanding this will be critical to understanding the chemistry of photosynthesis and how cells store and use energy.  Figure 2.7 on page 26 of your text, illustrates this characteristic of electrons.  Fig. 2.9.

Question:  This fundamental change in the essence of an atom, due to the addition of one proton, reminds me of:
a.  a headache 
b.  excitement boarding on euphoria
d.  emergent properties

If you were to add or remove an electron, you would still have helium, but the resulting atom would no longer have a balance of three protons (3 +'s) with with three electrons (3 -'s).  Assume you threw a neutron at a helium atom and knocked off an electron.  The resulting atom would no longer be electrically balanced or neutral; it would have one extra positive charge and would be written He⁺  and would be called a helium "ion."

• atoms are made out of protons, neutrons and electrons
• adding a proton to an atom transforms the atom into the next heaviest atom
• adding a neutron to an atom produces an isotope
• an isotope retains the characteristics of the original atom, but it's heavier
• some isotopes are "radioactive"
• electrons orbit the nucleus in electron orbits or "shells"
• the 1st electron orbital or "shell" holds up to 2 electrons
• the 2nd shell holds up to 8 electrons
• atoms appear "driven" to fill their outer shell, and will share electrons with other atoms until their outer shell is "full"
• adding or removing electrons produces ions
• ions have a + or - charge because the number of protons and electrons are not balanced
• ions are therefore attracted to opposite charged ions
• ions are important to many biochemical activities like running and thinking
• Gatorade contains sodium ions (Na+) and calcium ions (Ca+)

By continuing to add protons, neutrons and electrons, you could in theory assemble all the elements.  To see a chart listing the elements from smallest to largest, click on the link below.  Notice where H, He and Li are in the chart, and see if you understand how the periodic chart is organized.