What element in the fourth period of the periodic table has 5 valence electrons? How are chemical elements diffrent from chemical compounds? What does organic chemistry study? How do elements change from left to right in the periodic tabale?
See all questions in Elements. This is a greatly oversimplified explanation of acid-base chemistry. Hydrogen was discovered by the English chemist Henry Cavendish in ; hydrogen had been observed before, but Cavendish was the first to recognize not only that it was an element, but that it burned to form water, which also provided conclusive proof that water was not itself an element.
The name "hydrogen" was derived by the French chemist Antoine Lavoisier from the Greek words hydro "water" and genes "forming". There are three isotopes of hydrogen. Hydrogen-1, or protium , contains one proton in its nucleus, and is by far the most common form of hydrogen Hydrogen-2, or deuterium , contains one proton and one neutron in its nucleus, and comprises the remaining 0.
Hydrogen-3, or tritium , contains one proton and two neutrons, and is only found in trace amounts; it is produced by the interaction of cosmic rays on gases in the upper atmosphere, and in nuclear explosions, but since it has a half life of only Heavy water is water made from two atoms of deuterium and one atom of oxygen. This form of water is literally heavier than "ordinary" water, since an atom of deuterium is twice as heavy as an atom of "regular" hydrogen. H 2 O has a molar mass of Ordinary water contains about 1 molecule of D 2 O for every molecules of H 2 O.
The electrolysis of water concentrates D 2 O in the solution, since the lighter isotope evaporates from the solution slightly faster. Successive electrolysis experiments allow pure heavy water to be produced, but it takes about , gallons of water to produce 1 gallon of heavy water by this method. Heavy water is used as a moderator in nuclear reactions: it slows down fast-moving neutrons, allowing them to be captured more easily by other nuclei.
The generation of heavy water was important during the research on nuclear fission that went into the Manhattan Project during World War II. For a typical person, a fatal dose would require drinking nothing but heavy water for 10 to 14 days, so it's pretty doubtful that heavy water poisoning will be featured on CSI anytime soon. Most hydrogen is prepared industrially be reacting coal or hydrocarbons with steam at high temperatures to produce carbon monoxide and hydrogen gas a mixture of carbon monoxide and hydrogen is called synthesis gas , and can be used in manufacturing methanol.
On smaller scales it can be produced by the reaction of active metals such as zinc, calcium, etc. Hydrogen gas is combined with nitrogen in the Haber process to synthesize ammonia NH 3 , which is widely used in fertilizers.
It is also used in the manufacture of hydrogenated vegetable oils; in this reaction, hydrogen atoms add to the carbon-carbon double bonds in the vegetable oils double-bonded carbons bond to fewer hydrogen atoms than single-bonded carbons — i.
Another use for hydrogen is in rocket fuels: the Saturn V rockets that launched the Apollo lunar missions used , gallons of kerosene and , gallons of liquid oxygen in its first stage S-IC , , gallons of liquid hydrogen and 83, gallons of liquid oxygen in its second stage S-II , and 69, gallons of liquid hydrogen and 20, gallons of liquid oxygen in its third S-IVB stage; the Space Shuttle main engines use , gallons of liquid hydrogen and , gallons of liquid oxygen.
Hydrogen is lighter than air, and was used in balloons and dirigibles also known as airships or zeppelins. Dirigibles were used in city-to-city air travel in the early s, and in trans-Atlantic crossings in the s and s. During World War I, German zeppelins were used in bombing runs over England, since they could fly higher than the British planes.
On May 6, , the German dirigible Hindenburg caught fire as it came in for a landing at Lakehurst Naval Air Station in New Jersey; 35 people out of the 97 aboard and one person on the ground were killed.
The exact cause of the fire is still the subject of speculation, but the disaster signaled the beginning of the end for airship travel. Modern "blimps" use helium to provide lift, which avoids the problem of hydrogen's flammability. Molecules which contain hydrogen bonded to nitrogen, oxygen, or fluorine can attract one another through the formation of hydrogen bonds.
Hydrogen bonds are a particularly strong form of dipole-dipole forces , which arise because of the unequal sharing of electrons in some covalent bonds. If one atom in a covalent bond is more electronegative than the other, it "pulls" harder on the electrons that the two atoms share, giving the more electronegative atom a partial negative charge, and the less electronegative atom a partial positive charge. The partially negative atom on one molecule attracts the partially positive atom on a neighboring molecule, causing the two molecules to be more attracted to each other than two nonpolar molecules which have no electronegativity differences between their bonded atoms would be.
Molecules that interact by these dipole-dipole forces tend to have higher boiling points than nonpolar molecules, because higher temperatures are necessary to overcome the attractive forces between the molecules and separate the molecules into the gas phase.
In the case of O—H, N—H, and F—H bonds, the electronegativity differences are particularly large because fluorine, oxygen, and nitrogen are the most strongly electronegative elements.
The attractive forces between molecules containing these bonds are particularly strong, and are given the name hydrogen bonds. Hydrogen bonds are not as strong as covalent bonds, but they greatly influence the physical properties of many substances.
In particular, hydrogen bonds are responsible for the fact that water is a liquid at temperatures at which molecules of similar molecular mass are gases. For instance, hydrogen sulfide, H 2 S, which weighs Ice floats on liquid water because the hydrogen bonds hold the molecules into a more open, hexagonal array, causing the solid form to be less dense than the liquid form.
In living systems, hydrogen bonding plays a crucial role in many biochemical process, from the coiling of proteins into complex three-dimensional forms to the structure of the DNA double helix, in which the two strands of DNA are held together by the hydrogen bonding between their nucleic acids components. The subgroups within the metals are based on the similar characteristics and chemical properties of these collections.
Our description of the periodic table uses commonly accepted groupings of elements, according to the Los Alamos National Laboratory. Alkali metals: The alkali metals make up most of Group 1, the table's first column. Shiny and soft enough to cut with a knife, these metals start with lithium Li and end with francium Fr.
They are also extremely reactive and will burst into flame or even explode on contact with water, so chemists store them in oils or inert gases. Hydrogen, with its single electron, also lives in Group 1, but the gas is considered a nonmetal. Alkaline-earth metals: The alkaline-earth metals make up Group 2 of the periodic table, from beryllium Be through radium Ra.
Each of these elements has two electrons in its outermost energy level, which makes the alkaline earths reactive enough that they're rarely found alone in nature. But they're not as reactive as the alkali metals. Their chemical reactions typically occur more slowly and produce less heat compared to the alkali metals. Lanthanides: The third group is much too long to fit into the third column, so it is broken out and flipped sideways to become the top row of the island that floats at the bottom of the table.
This is the lanthanides, elements 57 through 71 — lanthanum La to lutetium Lu. The elements in this group have a silvery white color and tarnish on contact with air. Some chemistry students just enjoy learning about the science, while others are intrigued by the violent reactions that sometimes can occur.
Many chemistry classes have been enlivened by the demonstration of how reactive sodium is with water. In some instances, the demonstration has gone off safely.
Unfortunately, in other situations students and instructors have incurred serious injury due to their failure to observe proper safety precautions. One value of the periodic table is the ability to make predictions about the behavior of individual elements.
By knowing which group an element is in, we can determine the number of reactive electrons and say something about how that element will behave. The periodic table is arranged on the basis of atomic numbers number of protons in the nucleus. One of the valuable consequences of this arrangement is that we can learn a lot about the electron distribution in these atoms. The colors in the table below indicate the different groupings of atoms based on the location and number of electrons in the atom.
If we look at Group I red column , we see that it is labeled alkali metals. Also note the green H above the alkali metals. All of these elements have a similar configuration of outer-shell electrons see Table 1.
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