2. Look at the periodic table and use the atomic number and mass number of carbo
ID: 52394 • Letter: 2
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2. Look at the periodic table and use the atomic number and mass number of carbon and silicon to draw their atomic structure with electron distribution in the shells. What is a similarity that you notice between them? Why did nature choose carbon instead of silicon for forming the variety of chemicals used for structure and function of living organisms? Noble gases helium, argon and neon are nonreactive, whereas oxygen, hydrogen and carbon are classified as reactive elements. Explain what is responsible for this difference.Explanation / Answer
Explanation for why carbon is selected by nature instead of silicon to form livin organisms
The similarity between carbon and silicon in the atomic structure is both have 4 electrons in the outer shell Carbon -2,4 & Silicon- 2,8,4 (arrangement of electrons in the shells)
Life on Earth is carbon based. This simply means that the chemistry for life on Earth uses carbon to form complex molecules that are used for various life functions, such as information storage. We find carbon in everything from cell membranes, to hormones, to DNA. For years, scientists and science fiction writers have dreamt about the possibility of life based on something other than carbon. To replace carbon with another element, we would need to carefully choose a competitor. Carbon’s contender should be an element that is abundant since it will be a major constituent of so many vital molecules. In addition, we would need to consider elements that have the ability to bond with themselves as well as with a variety of other elements to create complex, and more importantly stable, molecules for life.
It is well known that different elements can possess similar chemical characteristics. These similarities stem from the fact that all atoms are essentially put together in the same way. The periodic table is an organized list of all the elements and is presented in such a way as to reflect patterns in the arrangement of the nuclear particles within atoms. For example, as you read the periodic table from left to right, the number of protons and electrons per atom increases. All of the elements in one column have the same number of electrons in their outer electron shells. Typically it is only the outer shell of electrons that plays a role in chemical reactions. This means that elements in the same column tend to participate in chemical reactions similarly. If
The periodic table of elements is ordered by the number of protons in the nucleus of an atom for a given element (the atomic number), yet the chart is also arranged in such a way that elements with similar characteristics are grouped together. Such is the case with Group 8, which is sometimes called Group 18, a collection of non-metals known as the noble gases. The six noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Their atomic numbers are, respectively, 2, 10, 18, 36, 54, and 86.
Several characteristics, aside from their placement on the periodic table, define the noble gases. Obviously, all are gases, meaning that they only form liquids or solids at extremely low temperatures—temperatures that, on Earth at least, are usually only achieved in a laboratory. They are colorless, odorless, and tasteless, as well as monatomic—meaning that they exist as individual atoms, rather than in molecules. (By contrast, atoms of oxygen—another gas, though not among this group—usually combine to form a molecule, O2
we look at the column that begins with carbon, we can read down the column and see that this column includes various other elements such as silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). In most of the fantasies about alien life, silicon is the candidate proposed to replace carbon since its location in the periodic table is directly beneath that of carbon. For the remainder of this discussion, we will compare silicon to carbon as the fundamental element of life.
Silicon has the same number of electrons in its outer shell, meaning that it can form four bonds just like carbon. It is also very abundant, comprising much of the rock that is beneath your feet. Silicon can bind readily to itself to make Si-Si bonds just like carbon can make C-C bonds. With just this information, one might think that we are on to something with this silicon atom. After all, C-C bonds are the basis for complex molecules on Earth. However, we are neglecting some rather important details. Although Si-Si bonds, as well as silicon-hydrogen and silicon-oxygen bonds, are easily made we have not yet considered the relative strengths of these bonds. Si-Si bonds are much weaker than C-C bonds – they are only half as strong! Si-H bonds and Si-O bonds are stronger than Si-Si bonds, whereas the carbon analogs for all three of these types of bonds are nearly equal in strength. This means that while it is very easy to create long chains and rings of carbon atoms, it is unusual to have long chains or rings of silicon atoms linked together. In fact, it is extremely rare to find any molecules that have strung together more than three silicon atoms.
Some of the more common carbon molecules that we are familiar with on Earth, such as carbon dioxide (CO2) and methane (CH4) do have silicon derivatives. Silicon is very attracted to oxygen and therefore combines readily with oxygen even at lower temperatures, forming silicon dioxide, SiO2. If silicon were to combine with the most abundant element in the universe, hydrogen, it would form silane, SiH4. However, silicon doesn’t react as easily with hydrogen as it does with oxygen. Even in the most reducing conditions and with plenty of excess hydrogen, silane won’t form below temperatures of 1000 K. And when you compare silane to methane, we notice that silane is much less stable than methane, igniting when exposed to air.
We have plenty of evidence of SiO2 formation on Earth, as it is a primary constituent of rocks. The most common form of SiO2 is quartz. Although commonly identified on Earth, SiO2 has vastly different properties than the also abundant CO2. Here on Earth, CO2 is gaseous at most temperatures, is very soluble in water (and is therefore available in aqueous solution for life), and can be broken down into carbon and oxygen. In stark contrast, SiO2 does not exist as a gas except at extremely high temperatures, well over 2000 degrees Celsius. As can probably be anticipated by the fact that it comprises many rocks on Earth, SiO2 is almost completely insoluble in everything. Finally, because silicon has a high affinity for oxygen, it is very difficult to break SiO2 into it constituent atoms. Consequently, carbon dioxide wins the competition against silicon dioxide for being most useful to life. With respect to living organisms, SiO2 can be considered a very inert molecule and therefore useless for life processes.
3.Helium, argon and neon are nonreactive because these gases form liquids and solids at extremely low temperatures - temperatures that are usually achieved only in the laboratory. They are colourless, odourless and tasteless and are monatomic-meaning that they exist as individual atoms rather than as molecules.These are called noble gases and thei lack chemical reactivity.Rather than reacting to, or bonding with, other elements, the noble gases tend to remain apart—hence the name "noble," implying someone or something that is set apart from the crowd, as it were. Due to their apparent lack of reactivity, the noble gases—also known as the rare gases—were once known as the inert gases.Nonetheless, low reactivity—instead of no reactivity, as had formerly been thought—characterizes the rare gases. One of the factors governing the reactivity of an element is its electron configuration, and the electrons of the noble gases are arranged in such a way as to discourage bonding with other elements.
Oxygen ,hydrogen and carbon are reactive elements
The stable elements(noble gases) already have 8 electrons in their valence shell, which is full, therefor, they wont react with other elements.
A reactive element needs to either gain or lose electrons to have a full valence shell. So, since the first column only needs to lose one electron, they are considered HIGHLY reactive. Also, the halogens (one column right of the noble gases) only need to gain one, so they are also highly reactive
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