Answer : Banana and fruit type, the process proceeds chemically
mature naturally. Carbohydrates in the womb flesh turned into glucose, which
create a sense of sweet and tender.
The process produces Ethylene Gas. Gas is creeping from one
to another molecule to make its surroundings so well cooked. This is the basis
to give Calcium carbide (Calcium Carbide), is used to assist the process of
maturation. Calcium carbide, carbide we call it, when hit the water or moisture
will produce Asetilin Gas. This gas in its chemical structure similar to
natural Ethylene. Because this is filled with gas Asetilin, the fruit will
ripen simultaneously ferment. Yes, if less ripe fruit will not as sweet as a
ripe, because the content Carbohydrates - Starch substances is still lacking.
Gas asetilin because light will fly and mixed with air.
because the fruits
which contain ethylene gas is natural gas, which was conceived young fruits or
young. chemical structure of ethylene = acetylene gas.
on, old fruit
ethylene gas concentrations increase, in order to accelerate the ripening of
fruit ...
Fruit ripening process naturally results in some natural
gases like water vapor, CO2 and acetylene (carbide gas = C2H2).
Chemically into storage if the fruit is also added carbide
it will spur the production of acetylene from the fruit ripening process will
mean faster. Carbide (CaC2) if in the open air will react with water vapor in
the air (H2O) bit by bit to produce acetylene (C2H2).
So that makes fruit
ripe hormone called ethylene gas (carbide = a trade name). Actually plants
naturally produce this hormone is for fruit to ripen. However, the carbide
pedagan add more fruit than normal levels for fruit to mature faster.
Use of this carbide does not cause negative impacts. Levels
of vitamins and minerals do not change because the use of this carbide. This is
because the carbide is a chemical that stimulates only pembntukan ethylene gas
which stimulates the ripening process of fruit. In addition, no significant
negative impacts to the health of consumers. Why do carbon afford to form duplicate bonting 1,2,3
Answer : Carbon chainsmay be eithera
single bond, double bond, ora triple bond. Forms
ofcarbon chainsthemselves are veryvaried, there isa
straight(unbranched), there isabranching, thereareopen,andthere isa closed(circular). Variousforms ofcarbon chainspresentedin the figurebelow.Why carbon can form so many compounds, with very varied types? Why is this not
happening in the adjacent element or elements are classified with the carbon in
the periodic table? BC has the electron configuration of atoms 2 4. The four
valence electrons distributed on the four C atoms in a symmetrical position.
The carbon atom has four valence electrons with the atomic radii price the
smallest of the atomic radius of other elements in the group IVA. It
facilitates the C atom to form covalent bonds with other atoms, especially with
atomic H, O, N, and halogen atoms (F, Cl, Br, and I). Covalent bonds are formed
to meet the octet rule. The carbon atom can form up to four covalent bonds.
Covalent bond formed by atoms C is more powerful than other covalent bonds, so
that the carbon compounds are stable.
The position of carbon atoms in the periodic table in the middle so it has a
moderate electronegativity value (2.5). This trait causes the carbon atoms can
bind atoms having electronegativity greater or even smaller. The carbon atom
can have a positive oxidation state (+2, +4), negative (-2, -4), or even zero.
Petroleum is also dubbed as the black gold, is a thick liquid, dark
brown or greenish flammable, which is in the upper layers of the few
areas in the earth's crust. Petroleum consists of a complex mixture of
different hydrocarbons, the majority of the alkane series, but vary in
appearance, composition, and purity. Oil extracted from oil wells in the
oil mines. Location of the wells is obtained after going through the
process of geological studies, sediment analysis, and the structure of
the source code, and various studies lainnya.Setelah, the Earth will be
processed in oil refineries where oil and split the results based on the
boiling point to produce a wide range of fuels, from gasoline and
kerosene to asphalt and other chemical reagents needed to make plastics
and pesticides obatan.Minyak Earth used to produce a wide range of goods
and material human needs.
Petroleum Establishment
The process of petroleum formation is described by two theories, namely: Inorganic Theory
Inorganic
theory proposed by Berthelok (1866) which states that petroleum derived
and the reaction of calcium carbide, CaC2 (and the reaction between
carbonate rocks and alkali metals) and water produces acetylene which
can be turned into oil at high temperature and pressure.
Alkali → CaC2 CaCO3 + HO + HC = CH → → Petroleum
Theory of Organic Organic
theory proposed by Engker (1911) which states that petroleum is formed
from the weathering and decomposition of anaerobic micro-organisms
(microorganisms) from marine plants in porous rocks.
Composition of Petroleum The composition of petroleum are classified into four groups, namely:
Saturated hydrocarbons (alkanes)
* Known as alkanes or paraffin * The presence of straight-chain as the main component (the highest), while the less branched chain * Compounds authors include:
* Known as a series of aromatic * Its existence as a minor component / bit * Compound formulation:
1.Naftalena 2.Antrasena 3. Benzene 4. Toluene
Other Compounds
* Existence is very little * Compounds that may be present in petroleum is sulfur, nitrogen, oxygen and organo metallic (very small)
Petroleum Processing Crude
oil gained from drilling a thick black liquid that utilization should
be processed first. Petroleum drilling in Indonesia, located on the
north coast of Java (Cepu, Wonokromo, Cirebon), Sumatra (Aceh, Riau),
Kalimantan (Tarakan, Balikpapan) and Irian (Papua). Petroleum processing
via two stages, including:
First Processing, At this stage do
"distillation separates stratified petroleum fractions based on boiling
point. Components of a higher boiling point will remain a liquid and
drops down. While a lower boiling point will evaporate and rise to the
top through sangkup-sangkup called sangkup bubble.
Secondary treatment, At this stage a further process refined stratified by the following process:
1. Cracking 2. Extraction 3. Crystallization 4. cleanup of contamination
Gasoline Gasoline composition of n - heptane and iso-octane, namely:
Substance Gasoline Additive
Tetra Ethyl Leat (TEL)
* The molecular formula Pb (C2H5) 4 * The formula
Ethyl Tertiary Butyl Ether (ETBE)
* The molecular formula CH 3 OC (CH3) 3Tersier Amil Methyl Ether (TAME)
* The molecular formula CH 3 OC (CH3) 2 C2H5Metir Buthil Tertiary Ether (MTBE)
* The molecular formula CH3 O C (CH3) 3
Petrochemicals
Other than petroleum as a fuel as well as
materials for the chemical industry is important in everyday life.
Materials or products made from basic ingredients of oil and gas are
called petrochemicals. Petrochemical materials can be classified:
plastics, synthetic fibers, synthetic rubber, pesticides, detergents,
solvents, fertilizers, various types of drugs and vitamins.
Petrochemical process generally through three stages, namely:
1. Change the oil and gas into petrochemical ingredients 2. Changing the basic petrochemical materials into intermediate products, and 3. Changing the intermediate products into final products that can be utilized.
Almost all petrochemical products derived from the three basic types of materials, namely:
1. Olefin (alkene-alkene) Olefin is the most important ethene (etilina), propene (propylene), butene (butylene) and butadiene.
CH2 = CH2 CH2 = CH - CH3
Ethylene propylene
CH3 - CH = CH - CH3 CH2 = CH - CH = CH2
Butylene butadiene
2. Aromatic (benzene and its derivatives) Aromatic most important is benzene (C6H6), totuena (C6H5CH3) and xylene (C6H4 (CH3) 2
3. Synthesis Gas
Synthetic gas called syn-gas which is a mixture of carbon monoxide (CO)
and hydrogen (H2). Syn-gas made from natural gas or LPG reaction
through a process called reforming or partial oxidation stean.
Here are some of the petrochemical ethylene olefin with basic ingredients:
1. Polyethylene Polyethylene is the most widely produced plastic are used as plastic bags and plastic wrappers / trash.
2. PVC PVC is a plastic that is polivinilkiorida pipe makers (pralon).
3. Ethanol Ethanol is an everyday material we know as the alcohol used for fuel or among other products.
Alcohol is made from ethylene:
CH2 = CH2 + H2O → CH3 - CH2OH
4. Ethylene glycol or glycols Glycol is used as an antifreeze in a car radiator in cold climates.
Here are some of the petrochemical olefins with propylene base material.
5. Polypropylene Polypropylene plastic is stronger than polyethylene. Type of polypropylene plastic used for plastic bags and a plastic strap.
6. Glycerol
This substance is used as an ingredient in cosmetics (moisturizers),
the food industry and the materials to make explosives (nitroglycerine)
7. Isopropyl alcohol
This substance is used as the main material for petrochemical products
such as acetone (a solvent, for example, to dissolve Kutek)
Petrochemical manufacturing using basic materials such as butadiene
synthetic rubber is SBR (styrene-butadilena-rubber) and nylon -6.6,
while those using the basic ingredients are isobutylene MTBE (methyl
tertiary butyl ether)
Petrochemicals from Aromatic
The
basic ingredients are the most important aromatics are benzene, toluene,
and xylene (BTX). The basic ingredients are generally converted into
styrene benzene, cumene, and cyclohexane
1. Styrene is used to make rubber sinetik 2. Cumene is used to make phenol, then phenol to make the adhesive 3. Cyclohexane is used primarily for making nylon
4. Benzene is used as a raw material for making detergents. The basic
ingredients for toluene and xylene to make explosives (TNT),
terephthalic acid (fiber fabric).
Petrochemical and gas-sinetik
Sinetik gas is a mixture of carbon monoxide and hydrogen. Several petrochemical examples of syn-gas as follows:
1. Ammonia (NH3)
N2 (g) + 3H2 (g) → 2NH3 (g)
Nitrogen gas from the air and hydrogen gas from the syn-gas. Ammonia
is used to make fertilizer [CO (NH2) 2] urea, [(NH4) 2SO4]; ZA and
(NH4NO3), ammonium nitrate.
2. Urea [CO (NH2) 2]
CO2 (g) + 2NH3 (g) → NH2COH4 (S)
NH2CONH4 (S) → CO (NH2) 2 (s) + H2O (g)
3. Methanol (CH3OH)
CO (g) + 2H3 (g) → CH3OH (g)
Most of the methanol is converted to formal-dehida and some are used to make fiber and fuel mixtures.
4. Formal dehida (HCHO)
CH3OH (g) → HCHO (g) + H2 (g)
Formal dehida in water known as formalin used to preserve biological preparations.
Of
the various chemical elements that we know .... there is an element
whose scope is very broad and very deep discussion on the CARBON. Carbon has an atomic number of 6 so the number of electrons is also 6 .... with configuration 6C = 2, 4. This
can be seen from the electron configuration C atom has four valence
electrons (electrons in the outer shell) ..... To obtain 8 electrons
(octet) in the outermost shell (valence electrons) needs 4 electrons so
that each search valence electrons with the atomic electron pairs -other atom. The specificity of the carbon atom is its ability to bind to other carbon atoms forming the carbon chain. Forms of carbon rantai2 the simplest hydrocarbon. Hydrocarbons are composed of two elements, namely hydrogen and carbon. Based on the number of other C atoms bonded to one C atom in the carbon chain, the C atom is divided into: a. Primary C atom, the C atom that binds the C atom to another.b. Secondary C atom, the C atom bound to two other C atoms.c. Tertiary C atom, the C atom that binds the other three C atoms.d. Kwarterner C atoms, the atom C that bind to four other C atoms.
• primary C atom, C atom number 1, 7, 8, 9 and 10 (green)• secondary C atom, C atom number 2, 4 and 6 (blue)• tertiary C atom, C atom number 3 (yellow)• kwarterner C atom, C atom number 5 (red) Based on the form of carbon chain: •
Hydrocarbons aliphatic hydrocarbons with chain = straight / open
saturated (single bond / alkanes) and unsaturated (double bond / alkene
or alkyne).• Hydrocarbons = alicyclic hydrocarbons with chain circular / closed (ring).•
Aromatic Hydrocarbons = hydrocarbons with chain circular (ring) having a
single bond between atoms C and dual alternately / alternating
(conjugated) Later in this article I discuss the limit of open-chain hydrocarbons (aliphatic) only ....Based on the existing bonds in the C chain, aliphatic hydrocarbons distinguished by:1. Alkanes (CnH2n +2)2. Alkenes (CnH2n)3. Alkynes (CnH2n-2) Description: n = 1, 2, 3, 4, etc. ....... Alkanes (Paraffin) is its hydrocarbon chain C consists of only a single covalent bonds only. often referred to as saturated hydrocarbons .... as the number of hydrogen atoms in the molecule tiap2 maximum. Understanding Alkanes nomenclature is vital, as the basis for naming senyawa2 other carbon. Properties of Alkanes1. Saturated hydrocarbons (no bond C atom duplicate so its maximum number of H atoms)2. Called paraffin as affinity groups small (little affinity)3. It is difficult to react4. Form
Alkanes with a chain C1 - C4 is a gas at room temperature, C4 - C17 is a
liquid at ambient temperature and> C18 is a solid at room
temperature5. Boiling
point is higher for C elements ... and if it increases the number of C
atoms together so that branches have a lower boiling point6. Solubility properties: easily soluble in non-polar solvents7. Density rose with increasing the number of elements of C8. Is a major source of natural gas and petroleum (crude oil)General formula CnH2n +2 Homologous series alkanes Homologous
series is a group / groups of carbon compounds with the same general
formula, have similar properties and between ethnic groups have
different berturutannya CH2 or in other words an open chain with no
branches or branches with the same number of branches. The properties of the homologous series of alkanes:o Have similar chemical propertieso Has the same general formulao The difference between the two tribes Mr berturutannya at 14o The longer the carbon chain, the higher the boiling point n Formula Name 1. CH4 = methane2. C2H6 = ethane3. C3H8 = propane4. Butane C4H10 =5. C5H12 = pentane6. C6H14 = hexane7. C7H16 = heptane8. Octane C8H18 =9. C9H20 = nonana10. C10H22 = decane11. C11H24 = undekana12. C12H26 = dodecane TATA NAME alkanes 1. Alkane name is based on the longest C chain as the main chain. If there are two or more chains are longest then selected the highest number of branches2. Branch C is a chain attached to the main chain. alkananya name written in front of the number and the name of the branch. Branch name matches the name alkanes by replacing the suffix with the suffix ana il (alkyl).3. If
there are several branches of the same, then the name of the branch
that is the same amount of C mentioned once but comes with a prefix that
states the amount of the entire branch. The
atomic number C where the branch is bound to be written as an existing
branch (which is written numbers = number prefix is used), which is at
= 2, tri = 3, tetra = 4, penta = 5 and so on.4. For a number of branches of C is different sorted in alphabetical order (first from methyl ethyl).5. Branch number was calculated from the end closest to the main chain with branches. If the location of the nearest branch with both starting from the same:• Branch first alphabet sequence (first of methyl ethyl)• Branches are more numerous (two first branches of the branch) Example:What is the name idrokarbon below?
The first time we set the main chain ..... the main chain is the longest chain:
main chain is in the red box ...... Why?? you
try to look at the left side, when the main chain is straight (line
putus2) then sama2 will increase 2 atom C but will only lead to one
branch (the part you turn down) .... whereas when we steered down there
will be 2 branches (Rule No. 1). Now
you try to look to the right, the explanation is more simple .... when a
straight main chain (line putus2) only increased by one C atom whereas
when turned down it will grow 2 atom C. So
it may be a series of major chains belak-turn and not be straight
...... origin still in one continuous sequence with no branches. The remaining carbon chain of the chain is the branch .....
look there are 3 branches namely 1 and 2 methyl ethyl branches numbering ..... we select the smallest number: •
if the end of the left side of the main chain ethyl C atom is located
in the main chain and methyl number 3 is located in the main chain C
atom number 2 and 6•
if the end of the right of the main chain ethyl C atom is located in
the main chain and methyl number 6 in the main chain C atom numbers 3
and 7 conclusions about sort of the tip of the left ..... Sequence naming: branch number - nana branch - the name of the parent chain so his name: 3 ethyl dimethyl octane 2.6
ethyl branch called earlier than methyl because his first name alphabetically first (alphabet "e" from the first "m"). because there are two methyl branches then simply called once plus the prefix "in" means "two". because the main chain consists of 8 main chain atom C then named: octane. Alkanes form skeletal structures undergo condensation sometimes ..... for example:
CH3 (green) is the end of the chainCH2 (blue) is the straight-chain tenganhCH (orange color) branching threeC (red) four branching Usefulness alkanes, as: • Fuel• Solvents• Sources of hydrogen• Lubricants• The raw material for other organic compounds• Raw materials industry Alkenes (Olefins) an unsaturated hydrocarbon compound that has one double bond 2 (-C = C-) Properties of Alkenes• Hydrocarbons unsaturated double bonds• alkene called olefins (oil forming)• more active physiological properties (as sleeping pills -> 2-methyl-2-butene)• Properties with Alkanes, but more reactive• Properties: colorless gas, can be burned, peculiar smell, explosive in the air (at a concentration of 3-34%)• There is the ordinary coal gas in the process of "cracking"General formula CnH2n
NAME of alkenes almost the same as naming Alkanes with a difference:• The main chain must contain the double bond and selected the longest. Name the major chains are also similar to alkanes by replacing the suffix-ana-ene. So
the selection of the longest chain of C atoms starting from C dual to
the right and left and the right and left selected the longest.•
Numbers written bond position in front of the main chain and is
calculated from the tip to the location of the double bond C its
smallest sequence number.• Sequence number position as branch chain numbering sequence fagots main chain.Example:
calculation
of C atoms in the main chain starting from the left side of the double
bond bond .... there is only one option bond while the right there are
two options, namely the first straight and bend down .... kedua2nya
sama2 adding 4 C atoms, but when it turns produced only one first down when a straight branch while causing two branches. So his name: 3 ethyl 4 methyl 1 pentena 1 pentena can be replaced by n-pentena or special bonds at number one should not be written .... so the name quite: pentena. Branch number equal to the number sequence sorted double bond. In question at the top of the right end .... Uses Alkenes as:• Can be used as an anesthetic (mixed with O2)• To ripen fruit• industrial raw materials plastics, synthetic rubber, and alcohol
alkyne
anunsaturatedhydrocarboncompoundshavingonedouble bond3 (-C≡C-).The natureis the same asalkenesbut morereactive.
A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.[1] Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles (such as illustrated by Feynman diagrams), as well as nuclear reactions.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell.
In the late 1890s, the Scottish chemist Sir William Ramsay discovered the elements helium, neon, argon, krypton, and xenon. These elements, along with radon, were placed in group VIIIA of the periodic table and nicknamed inert (or noble) gases because of their tendency not to react with other elements (see our Periodic Table page). The tendency of the noble gases to not react with other elements has to do with their electron configurations. All of the noble gases have full valence shells; this configuration is a stable configuration and one that other elements try to achieve by reacting together. In other words, the reason atoms react with each other is to reach a state in which their valence shell is filled.
Let's look at the reaction of sodium with chlorine. In their atomic states, sodium has one valence electron and chlorine has seven.
Sodium
Chlorine
Chlorine, with seven valence electrons, needs one additional electron to complete its valence shell with eight electrons. Sodium is a little bit trickier. At first it appears that sodium needs seven additional electrons to complete its valence shell. But this would give sodium a -7 electrical charge and make it highly imbalanced in terms of the number of electrons (negative charges) relative to the number of protons (positive charges). As it turns out, it is much easier for sodium to give up its one valence electron and become a +1 ion. In doing so, the sodium atom empties its third electron shell and now the outermost shell that contains electrons, its second shell, is filled - agreeing with our earlier statement that atoms react because they are trying to fill their valence shell.
Sodium Chloride
This trait, the tendency to lose electrons when entering into chemical reactions, is common to all metals. The number of electrons metal atoms will lose (and the charge they will take on) is equal to the number of electrons in the atom's valence shell. For all of the elements in group A of the periodic table, the number of valence electrons is equal to the group number (see our Periodic Table page).
Nonmetals, by comparison, tend to gain electrons (or share them) to complete their valence shells. For all of the nonmetals, except hydrogen and helium, their valence shell is complete with eight electrons. Therefore, nonmetals gain electrons corresponding to the formula = 8 - (group #). Chlorine, in group 7, will gain 8 - 7 = 1 electron and form a -1 ion.
Hydrogen and helium only have electrons in their first electron shell. The capacity of this shell is two. Thus helium, with two electrons, already has a full valence shell and falls into the group of elements that tend not to react with others, the noble gases. Hydrogen, with one valence electron, will gain one electron when forming a negative ion. However, hydrogen and the elements on the periodic table labeled metalloids, can actually form either positive or negative ions corresponding to the number of valence electrons they have. Thus hydrogen will form a +1 ion when it loses its one electron and a -1 ion when it gains one electron.
Reaction energy
All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. For example, sodium and chlorine react so violently that flames can be seen as the exothermic reaction gives off heat. On the other hand, some reactions need to absorb heat from their surroundings to proceed. These reactions are called endothermic. A good example of an endothermic reaction is that which takes place inside of an instant '"cold pack." Commercial cold packs usually consist of two compounds - urea and ammonium chloride in separate containers within a plastic bag. When the bag is bent and the inside containers are broken, the two compounds mix together and begin to react. Because the reaction is endothermic, it absorbs heat from the surrounding environment and the bag gets cold.
Reactions that proceed immediately when two substances are mixed together (such as the reaction of sodium with chlorine or urea with ammonium chloride) are called spontaneous reactions. Not all reactions proceed spontaneously. For example, think of a match. When you strike a match you are causing a reaction between the chemicals in the match head and oxygen in the air. The match won't light spontaneously, though. You first need to input energy, which is called the activation energy of the reaction. In the case of the match, you supply activation energy in the form of heat by striking the match on the matchbook; after the activation energy is absorbed and the reaction begins, the reaction continues until you either extinguish the flame or you run out of material to react.
We need to start with a little chemistry because living organisms are made of and use chemicals.
Individual substances are called elements, substance which cannot be broken down or subdivided by ordinary chemical means. We recognize about 105 or 106 elements. About 92 are natural and the rest are man-made. These are things like oxygen, sulfur, carbon, copper, etc. Each element has a symbol made of the first letter or two of its name. Some are from the old Latin names: sodium = natrium, iron = ferrum, potassium = kalium. Of the 92 naturally-occurring, four of these make up about 96% of all living matter. These are carbon, oxygen, hydrogen, and nitrogen, and the name COHN can help you remember these. Another 21 are needed in smaller amounts in order to live and stay healthy.
One piece, one particle of an element is an atom a unit of matter or the smallest possible amount of an element. Two or more atoms can bond together to form a molecule. Often the compound thus formed has properties quite different from the elements in it. For example, sodium (Na), an extremely reactive, nearly explosive metal, and chlorine (Cl), a toxic gas combine to form sodium chloride (NaCl), which is common table salt.
Atoms are made up of even smaller things called subatomic particles. There are three main types: proton (which has a very small positive electrical charge), neutron (which is neutral), and electron (which has a very small, negative electrical charge). You may see these referred to as p+, e–, and no. The protons and neutrons form the nucleus of the atom (not to be confused with the nucleus of a cell), while the electrons are zipping around them somewhere and are traveling at about the speed of light.
The number of protons is important: this determines what element something is. Each element has a different number of protons, and if the number of protons in an atom changes, then it what element it is. The number of protons in an atom is called its atomic number. This is written as a subscript to the left: 8O, 6C, etc.
Within limits, the number of neutrons and electrons in an atom can vary. Isotopes are atoms of the same element with different numbers of neutrons. Protons and neutrons weigh about the same as each other, but electrons are so much smaller, their weight is negligible by comparison (like carrying a feather when you weigh yourself on the bathroom scale). Thus, when we want to know how much an atom of something weighs, we can just add up the number of protons and neutrons. The number of protons plus the number of neutrons in an atom = its atomic weight. These are written as superscripts to the left: 12C, 13C. Atomic weight minus atomic number equals the number of neutrons. This means that Carbon-12 has 6 neutrons, Carbon-13 has 7, and Carbon-14 has 8. In Carbon-14, the ratio of neutrons to protons (8 to 6) is far enough off that the nucleus of the atom is not stable, but undergoes radioactive decay, in which it turns into some other chemical (beyond the scope of this course, but if you are interested, the actual radioactive reaction, called -emission, is 614C 714N + e–, and the electron that is “kicked out” is called a beta [] particle). The half life of a radioactive chemical is the amount of time it takes for half of the starting quantity to undergo radioactive decay. Thus, if you started with 1 gm of a substance with a half life of 1 year, after one year, you would have 0.5 gm left, after two years you would have only 0.25 gm, after three years, 0.125, etc.
Molecular weight equals the sum of the atomic weights of the atoms in the molecule. For NaCl, the atomic weight of sodium is 23, of chlorine is 35 and a molecule contains one sodium and one chlorine, so 23 + 35 = 58, the molecular weight of NaCl. The formula for glucose ( a very common sugar) is C6H12O6. The subscripts to the right mean that it contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. The atomic weight for carbon is 12, for hydrogen is 1, and for oxygen is 16, so the molecular weight of glucose can be calculated thus:
Element
Atomic
Weight
No. of
Atoms
Total
Weight
C
12
6
6
×
12
= 72
H
1
12
12
×
1
= 12
O
16
6
6
×
16
= 96
Total = Molecular Weight
180
Use the Periodic Table below to help you with this molecular weight practice problem. (You’ll get a different problem each time you click this link.)
The numbers we will see listed on the periodic table are averages, For example, for carbon the number given is an average atomic weight of all the Carbon-12, Carbon-13, and Carbon-14 in the world. For our purposes, it’s OK if you round to the nearest whole number (C = 12, O = 16).
Normally, the number of protons and electrons match so the charge is balanced out. Sometimes, however, the number of electrons can vary. Ions are atoms with electrons added or removed resulting in an overall positive or negative charge. Generally, the charge on an ion is indicated to the upper right of its symbol. For example, a calcium ion with a +2 charge would be indicated as Ca++ or Ca+2. Electrons are moving rapidly all around the atom, and can possess certain discrete quantities of energy (like making change where you might have either a penny or a nickel or a dime, but not a 3.5 ¢ coin). These quantities are referred to as energy shells or orbitals. These are not orbits like the planets around the sun, but an attempt to show the energy quantities as pictures.
Each energy quantity/level/shell can only have a certain number of electrons with that much energy, kind of like if you would go to a movie where there are 1, 5, and 10¢ seats. The first energy level can have two electrons (there are two 1¢ seats). If there are more electrons, they must have the next amount of energy (they have to buy 5¢ seats), or as a chemist would say, they’re filling the second energy shell. Eight electrons can have the second level of energy (eight 5¢ seats). If there are still more electrons in the atoms of a particular element, then they must go into the third energy shell (buy 10¢ seats) where there are another eight spots available. Beyond that, things get too complicated for biology, so we’ll leave that to the chemists.
Chemists, however, prefer not to think in terms of 1, 5, and 10¢ seats at a movie. Often, the energy orbitals/shells are pictured as circles around the center of the atom. Again, the electrons do NOT travel around these circles like planets. Rather, this is just a way of showing how much energy they have. Our movie seats would convert to “standard” orbitals something like this.
This is how a chemist would diagram the energy levels of this atom. Notice that the electrons come in pairs. That idea is important in showing how atoms bond with each other to form molecules. Thus, the first energy level can have one pair of electrons, the second level can have four pairs, etc.
As atoms of different elements gain increasing numbers of electrons, one is put into each pair in a level before the second “half” of each pair is filled. Thus, for carbon, with six protons and six electrons, two of the electrons fill the available pair in the first energy shell. The remaining four electrons distribute themselves, one in each of the four pairs in the second level.
Electrons like to have the least amount of energy possible, so these levels will fill “from the bottom up” (they all fill the cheap seats first), thus not all atoms have electrons in all shells. The number of electrons in each of the shells depends on how many total electrons they have. This number is generally the same as the number of protons because the electrical charge of an electron is equal but opposite to that of a proton. Thus, hydrogen has one electron in the first level, helium has two in the first level, lithium has two in the first and one in the second level, etc. Note the arrangement of the periodic table: elements are organized into columns by how many electrons they have in their outermost energy levels (for example, H, Li, and Na each have one electron in whichever energy level is “outermost”), and organized into rows by which energy level (1st, 2nd, etc.) they’re filling (for example, Li, C, and N all have their first energy level full and are in various stages/numbers of electrons of filling their second level).
Periodic Table
For any element, the electrons in the outermost energy level/shell are the most important. These determine an element’s chemical properties – how it will react in a chemical reaction. These important electrons are known as the valence electrons. Know how many valence electrons carbon, oxygen, hydrogen, nitrogen, sodium, and chlorine have.
All elements are most stable with a full outer energy level, whatever that level is, so they will gain or give up electrons to make whatever is the outermost level be full even if it doesn’t match with the number of protons in that atom. This would be an ion, and if the atom gained electrons to form an ion (there are more electrons than protons), then its overall electrical charge would be negative by however many “extra” electrons it has. If an atom gives up electrons to form an ion (there are more protons than electrons), then its overall charge is positive.
Consider sodium and chlorine. Sodium is in column I so it has one valence electron. If it could get rid of that one, lonely electron from level 3, then its outer level would be level 2 which is nice and full. Chlorine is in column VII, so it has seven valence electrons, one short of a full outer shell. Thus, it would be more stable if it could grab an electron from somewhere to fill up that one, last spot.
Thus, when sodium and chlorine come together, in an explosive reaction, chlorine grabs sodium’s “unwanted” electron. This forms sodium ions with a +1 electrical charge (extra proton because it lost an electron) and chloride ions with a –1 charge. Chemists would write this as Na + Cl Na+ + Cl–. These positive and negative ions are still strongly attracted to each other, forming ionic bonds, bonds in which one atom grabs electrons from another. When compounds with ionic bonds are put into water, the ions come apart and dissolve in the water.
Because carbon has four valence electrons, one in each of the four pairs, it is more willing to share electrons with another atom (rather than grabbing them or giving them up). For example, methane is one atom of carbon bonded to four atoms of hydrogen. This would have the chemical formula, CH4. When atoms share electrons as they bond together, this is called a covalent bond. Many compounds with covalent (co- = with, together; valent = strength) bonds are not water soluble. Carbon can also form covalent bonds with other atoms of carbon, thus making long, stable chains possible. These are very important to living organisms.
The shape of a molecule of methane is a tetrahedron. The hydrogen nuclei (one proton each) are all “trying” to get as close as possible to all the electrons around the carbon, yet keep as far away as possible from each other (like + and – poles on a magnet). In a tetrahedron, there are four sides, all of which are triangles (in a pyramid, the bottom is square and there are five sides). The hydrogen protons are equally spaced in three dimensions around the carbon.
As a review, we have discussed the placement of four numbers around an element’s symbol (atomic number, atomic weight, charge, and number of atoms in a molecule), but all four are rarely used simultaneously. Just an an illustration, suppose a molecule of sodium carbonate is made with radioactive sodium-24 and then dissolved in water to form sodium ions (recall that sodium’s atomic number is 11). To indicate that there are two atoms of that sodium in the sodium carbonate, we would write “Na2CO3,” and if we wanted to indicate that they are sodium-24, we could rewrite this as “24Na2CO3,” or maybe even “1124Na2CO3.” Once the compound is dissolved in water, forming sodium ions, we would use “Na+” or maybe, in a rare situation, “24Na+” or “1124Na+” to indicate those ions, but since they are floating in the water and not attached to the carbonate (CO3–2) ion, now we don’t use the “2” after the “Na”. Note: if I’m using WordPerfect, I can put the superscripts and subscripts directly over/under each other (for example ), but HTML doesn’t do that.
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass ("go") between electrodes in a solution, when an electric field is applied. It is from Greek ιον, meaning "going".
Hydrogen atom (center) contains a single proton and a single electron. Removal of the electron gives a cation (left), whereas addition of an electron gives an anion (right). The hydrogen anion, with its loosely held two-electron cloud, has a larger radius than the neutral atom, which in turn is much larger than the bare proton of the cation. Hydrogen forms the only cation that has no electrons, but even cations that (unlike hydrogen) still retain one or more electrons, are still smaller than the neutral atoms or molecules from which they are derived.
-emission, is 
), but HTML doesn’t do that. 
