Biology (chapter 2)

Dylan Roscover Biology STS 1st hour 2006 10 01 Chapter 2 1. atom – The smallest unit of matter that still retains the properties of an element. They are very small and cannot be seen through the naked eye, let alone modern microscopes. compound – A substance consisting of two or more elements combined in a fixed ratio. Table Salt is a good example of a compound. element – A substance that cannot be broken down to other substances by chemical reactions. There are 92 total elements that we know of today. Some examples include gold, copper, carbon, and oxygen. matter – Anything that takes up space and has mass, not weight. It exists in various forms, with various characteristics. Trace elements are those required by an organism in only small quantities. An examples of this would be iron. The four primary elements are essential to life, and include Nitrogen, Oxygen, Carbon and Hydrogen. There are, in total, 25 "essential to life" elements, including the four primary elements. Naturally occurring elements are those found in nature (not in the lab), and there are 92 of them in total. 3. An isotope is a certain form of a certain element. Carbon, for example, has three different isotopes. The most common is carbon-12, which has 6 neutrons. There is also carbon-13 and carbon-14, with 7 and 8 neutrons, respectively. Only the neutron number varies in an element's isotope, electrons and protons stay the same, otherwise they would be different elements. A radioactive isotope is one in which the nucleus decays spontaneously (at once... heh), giving off particles and energy (lots of). When this decay leads to a change in the number of protons, this element becomes a different one. The positive applications for this are of course for biologists to measure the dates of past life and trace atomic metabolism, though radioactivity, as we all know, does pose a grave hazard to life by damaging cellular molecules. heh 5. An atom with a completed valence shell (aka, 8 valence electrons, 0 valence) is chemically un-reactive. It will not interact readily with other atoms it encounters. Some elements, such as helium, neon, and argon, have full valence shells. They don't react. At least, not usually. Hence the term, "inert." However, other elements, like carbon and oxygen, don't have full valence shells, so they react often with other elements. Carbon and hydrogen, for example, will form compounds readily (water) because they are

reactive, and pair evenly with each other. Some elements like noble gases won't because they don't pair up with any other elements... their shells are full. 7. A covalent bond is the sharing of a pair of valence electrons by two atoms. A double covalent bond occurs molecules share two pairs of valence electrons, instead of one pair in a single covalent bond. A non-polar covalent bond occurs when two atoms are equally electronegative: the electrons are shared equally. A polar covalent bond occurs when one atom is more electronegative than the other, and thus atoms are not shared equally, hence the polarity. On a whole new matter (heh... matter), an ionic bond occurs when cations and anions attract to each other as opposites. A hydrogen bond occurs when a hydrogen atom (duh) covalently bonds to one electronegative atom, which is also attracted to another electronegative atom. A van der Waals interaction is based on ever-changing "hot spots" of positive and negative charges that enable all atoms and molecules to stick to one another. So, yeah. There you have it. As you can clearly see, each has a different mechanism by which it forms and their relative bond strengths vary significantly. The movement of electrons within the electron cloud is one of great orbiting, each electron orbiting the nucleus at a ridiculously high velocity. The actual shape of the orbit may vary, but for the most part it is circular and similar to that which we see in all the visual figures and such. Yup. That's all.