Repaso biolgia

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  • Publicado : 30 de noviembre de 2011
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2.1 Start With atoms

* Each elements unique properties start with the number of protons in its atoms.
* An element is a fundamental substance made of only one kind of atom.
* Atoms are built from three different kinds of subatomic particles: protons, neutrons and electrons.
* Each proton carries a positive charge, which is a defined amount of electricity. You can symbolize aproton as p +.
* An atom’s nucleus or core region, holds one or more protons. Except for the hydrogen atom, it also holds neutrons which carry no charge.
* Moving around the atomic nucleus are one or more electrons, which carry a negative charge .
* The positive charge of an proton and the negative charge of one electron balance each other. Therefore, an atom that has the same numberof electrons and protons has no net electrical charge.
* Each element requires a unique atomic number, which is the number of protons in the nucleus of its atoms.
* A hydrogen atom has one proton, so the atomic number is 1. For carbon, is six protons, it is 6.
* Protons and neutrons contribute to an atom’s mass.
* We can assign each element a mass number, or the total of protonsand neutrons in the atomic nucleus.
* For carbon, with six protons and six neutrons, the mass number is 12.
* Why bother with the number of electrons, protons and neutrons?
* Knowing them can help you predict how each kind of element will behave under a variety of conditions inside and outside the body.
* Elements where being classified in terms of chemical similaritieslong before their subatomic particles were discovered.
* In 1869, Dmitry Mendeleev, arranged the known elements in a repeating pattern, based on their chemical properties.
* By using gaps in this periodic table of elements, Mendeleev correctly predicted the existence of many elements that has not yet been discovered.
* Elements fall into order in the table according to their atomicnumber.
* All elements in each vertical column would have the same number of electrons that are avaible for interaction with other atoms.
* They behave in similar ways.
* For example, helium, neon, radon, and other gases in the farthest right column of the periodic table are inert elements.
* Not one of their electrons in their atoms is available for chemical reactions. They occurmostly as solitary atoms.
* Those after atomic number 92 are extremely unstable. Some have been formed in exceedingly small qualities in laboratories.
* Atom= Smallest unit that retains an element’s properties.

2.2 Putting Radioisotopes to Use
* All elements are defined by the number of protons in their atoms, but an element’s atoms can differ in their number of neutrons.
* Wecall such atoms isotopes of the same element. Some are radioactive.
* Uranium has fifteen isotopes.
* Most naturally occurring substances do. Carbon has three isotopes and nitrogen has two.
* A subscript number to the left of an element’s symbol is the isotope’s mass number.
* For instance carbon’s three natural isotopes are 12c( carbon 12 the most common form, with six protons, sixneutrons), 13c( with six protons and seven neutrons), and 14c( six protons and eight neutrons.)
* Some isotopes are unstable or radioactive.
* A radioisotope spontaneously emits energy in the from of subatomic particles and x-rays when its nucleus disintegrates. This process is called radioactive decay, and transforms one element into another.
* Researchers use radioactive decay toestimate the age of biological rocs and biological remains.
* The different isotopes of an element are still the same element. For the most part, carbon is carbon, regardless of how many neutrons it has.
* Living systems use 12c the same as 14c.
* Knowing this researchers or clinicians who want to track a particular substance construct a tracer.
* Tracers are molecules in which...
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