Alkali metals how many valence electrons

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. In this technique, a sample is placed in a powerful magnetic field usually produced by a superconducting magnet — see the section on Helium , which causes the hydrogen atoms in the sample to resonate between two different magnetic energy levels; pulsing the sample with a burst of radiofrequency radiation typically between to MHz causes the hydrogen atoms to absorb some of this radiation, producing a readout called an "NMR spectrum" which can be used to deduce a great deal of structural information about organic molecules.

Since almost all organic molecules contain hydrogen atoms, this technique is widely used by organic chemists to probe molecular structure; it can also be used to determine a great deal of information about extremely complex molecules such as proteins and DNA.

The technique is nondestructive, and only requires small amounts of sample. NMR spectroscopy can also be performed with the carbon isotope, and several other isotopes of other elements. This technology is also used in an important medical imaging technique called Magnetic Resonance Imaging MRI ; the water molecules in different environments in the body respond to very slightly different magnetic field strengths, allowing images of tissues and organs to be obtained.

This technique can be used in diagnosing cancers and creating images of tumors and other diseased tissues. MRI is also used to study how the brain works by looking at what areas of the brain "light up" under different stimuli.

The term "nuclear" is avoided in the medical application because of its unpleasant associations, even though the only radiation involved is similar to that of an FM radio transmitter. Lithium is a soft, silvery metal, with a very low density, which reacts vigorously with water, and quickly tarnishes in air. The name of the element is derived from the Greek word for stone, lithos.

It is found in the Earth's crust at a concentration of 20 ppm, making it the 31st most abundant element. Lithium also presents some exceptions to the "typical" Group 1A behaviors. The lithium ion has a very high charge density because of its small size; thus, many lithium salts have significant covalent-bonding character, instead of being purely ionic.

Take the number of the group up and down the alkali metal is in. That is the number of the valence electrons. I know this is a bit late but if it isn't an ion then it will have 1 valence electron, witch is what makes it so reactive. Answer Question. Connect Connect Connect. They also have low boiling points, explaining why they are gases at room temperature. Radon, at the bottom of the group, is radioactive, so it constantly decays to other elements. For an excellent overview of the noble gases, watch the video at this URL:.

Q: Based on their position in the periodic table Figure above , how many valence electrons do you think noble gases have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period row of the periodic table for groups 1—2 and 13— Therefore, noble gases have eight valence electrons.

Noble gases are the least reactive of all known elements. The only exception is helium, which has just two electrons. But helium also has a full outer energy level , because its only energy level energy level 1 can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons.

Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements. Noble Gases and the Octet Rule. Because the noble gases are the least reactive of all elements, their eight valence electrons are used as the standard for nonreactivity and to explain how other elements interact.

According to this rule, atoms react to form compounds that allow them to have a group of eight valence electrons like the noble gases. For example, sodium with one valence electron reacts with chlorine with seven valence electrons to form the stable compound sodium chloride table salt. In this reaction, sodium donates an electron and chlorine accepts it, giving each element an octet of valence electrons.

Did you ever get helium balloons like those in the opening picture? A: Helium atoms have just two protons , two neutrons , and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down.

The filaments quickly burned out. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass. Filling a light bulb with argon gas prevents these problems. This protects the filament and keeps the glass blub free of deposits. Noble gases are also used to fill the glass tubes of lighted signs like the one in the Figure below. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them.

When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Krypton gives off violet light and xenon gives off blue light. This is the most stable arrangement of electrons, so noble gases rarely react with other elements and form compounds. Compare and contrast the reactivity of the elements helium, neon, argon, krypton, and xenon.

Compare the density of these noble gases to the density of air. Describe how the mass of noble gases changes from the top to the bottom of group In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of two; and in hydrogen chloride, chlorine has a valence of 1.

Chlorine, as it has a valence of one, can be substituted for hydrogen, so phosphorus has a valence of 5 in phosphorus pentachloride, PCl 5.

Valence diagrams of a compound represent the connectivity of the elements, lines between two elements, sometimes called bonds, represented a saturated valency for each element. Valence only describes connectivity, it does not describe the geometry of molecular compounds, or what are now known to be ionic compounds or giant covalent structures. The line between atoms does not represent a pair of electrons as it does in Lewis diagrams.

Valence Electrons.