viernes, 27 de febrero de 2009
lunes, 2 de febrero de 2009
PROPERTIES OF THE GROUPS OF THE PERIODIC TABLE
Alkali Metals
Properties of Element Groups
The alkali metals exhibit many of the physical properties common to metals, although their densities are lower than those of other metals. Alkali metals have one electron in their outer shell, which is loosely bound. This gives them the largest atomic radii of the elements in their respective periods. Their low ionization energies result in their metallic properties and high reactivities. An alkali metal can easily lose its valence electron to form the univalent cation. Alkali metals have low electronegativities. They react readily with nonmetals, particularly halogens.
Summary of Common Properties
· Lower densities than other metals
· One loosely bound valence electron
· Largest atomic radii in their periods
· Low ionization energies
· Low electronegativities
· Highly reactive
Metals
Properties
Metals are shiny solids are room temperature (except mercury), with characteristic high melting points and densities. Many of the properties of metals, including large atomic radius, low ionization energy, and low electronegativity, are due to the fact that the electrons in the valence shell of a metal atoms can be removed easily. One characteristic of metals is their ability to be deformed without breaking. Malleability is the ability of a metal to be hammered into shapes. Ductility is the ability of a metal to be drawn into wire. Because the valence electrons can move freely, metals are good heat conductors and electrical conductors.
Summary of Common Properties
· Shiny 'metallic' appearance
· Solids at room temperature (except mercury)
· High melting points
· High densities
· Large atomic radii
Nonmetals
Properties
Nonmetals have high ionization energies and electronegativities. They are generally poor conductors of heat and electricity. Solid nonmetals are generally brittle, with little or no metallic luster. Most nonmetals have the ability to gain electrons easily. Nonmetals display a wide range of chemical properties and reactivities.
Summary of Common Properties
· High ionization energies
· High electronegativities
· Poor thermal conductors
· Poor electrical conductors
· Brittle solids
· Little or no metallic luster
· Gain electrons easily
Metalloids or Semimetals
Properties
The electronegativities and ionization energies of the metalloids are between those of the metals and nonmetals, so the metalloids exhibit characteristics of both classes. Silicon, for example, possesses a metallic luster, yet it is an inefficient conductor and is brittle. The reactivity of the metalloids depends on the element with which they are reacting. For example, boron acts as a nonmetal when reacting with sodium yet as a metal when reacting with fluorine. The boiling points, melting points, and densities of the metalloids vary widely. The intermediate conductivity of metalloids means they tend to make good semiconductors.
Summary of Common Properties
· Electronegativities between those of metals and nonmetals
· Ionization energies between those of metals and nonmetals
· Possess some characteristics of metals/some of nonmetals
· Reactivity depends on properties of other elements in reaction
· Often make good semiconductors
Alkaline Earth Metals
The alkaline earths possess many of the characteristic properties of metals. Alkaline earths have low electron affinities and low electronegativities. As with the alkali metals, the properties depend on the ease with which electrons are lost. The alkaline earths have two electrons in the outer shell. They have smaller atomic radii than the alkali metals. The two valence electrons are not tightly bound to the nucleus, so the alkaline earths readily lose the electrons to form divalent cations.
Summary of Common Properties
· Two electrons in the outer shell
· Low electron affinities
· Low electronegativities
· Readily form divalent cations.
Transition Metals
Because they possess the properties of metals, the transition elements are also known as the transition metals. These elements are very hard, with high melting points and boiling points. Moving from left to right across the periodic table, the five d orbitals become more filled. The d electrons are loosely bound, which contributes to the high electrical conductivity and malleability of the transition elements. The transition elements have low ionization energies. They exhibit a wide range of oxidation states or positively charged forms. The positive oxidation states allow transition elements to form many different ionic and partially ionic compounds. The formation of complexes causes the d orbitals to split into two energy sublevels, which enables many of the complexes to absorb specific frequencies of light. Thus, the complexes form characteristic colored solutions and compounds. Complexation reactions sometimes enhance the relatively low solubility of some compounds.
Summary of Common Properties
· Low ionization energies
· Positive oxidation states
· Very hard
· High melting points
· High boiling points
· High electrical conductivity
· Malleable
HALOGENS
These reactive nonmetals have seven valence electrons. As a group, halogens exhibit highly variable physical properties. Halogens range from solid (I2) to liquid (Br2) to gaseous (F2 and Cl2) at room temperature. The chemical properties are more uniform. The halogens have very high electronegativities. Fluorine has the highest electronegativity of all elements. The halogens are particularly reactive with the alkali metals and alkaline earths, forming stable ionic crystals.
Summary of Common Properties
· Very high electronegativities
· Seven valence electrons (one short of a stable octet)
· Highly reactive, especially with alkali metals and alkaline earths
NOBLE GASSES
Location on the Periodic Table
The noble gases, also known as the inert gases, are located in Group VIII of the periodic table. Group VIII is sometimes called Group O.
Properties
The noble gases are relatively nonreactive. This is because they have a complete valence shell. They have little tendency to gain or lose electrons. The noble gases have high ionization energies and negligible electronegativities. The noble gases have low boiling points and are all gases at room temperature.
Summary of Common Properties
· Fairly nonreactive
· Complete valence shell
· High ionization energies
· Very low electronegativities
· Low boiling points (all gases at room temperature)
RARE EARTH
The Bottom of the Periodic Table
When you look at the Periodic Table, there is a block of two rows of elements located below the main body of the chart. These elements, plus lanthanum (element 57) and actinium (element 89), are known collectively as the rare earth elements or rare earth metals. Actually, they aren't particularly rare, but prior to 1945, long and tedious processes were required to purify the metals from their oxides. Ion-exchange and solvent extraction processes are used today to quickly produce highly pure, low-cost rare earths, but the old name is still in use. The rare earth metals are found in group 3 of the periodic table, and the 6th (5d electronic configuration) and 7th (5f electronic configuration) periods. There are some arguments for starting the 3rd and 4th transition series with lutetium and lawrencium rather than lanthanum and actinium.
There are two blocks of rare earths, the lanthanide series and the actinide series. Lanthanum and actinium are both located in group IIIB of the table. When you look at the periodic table, notice that the atomic numbers make a jump from lanthanum (57) to hafnium (72) and from actinium (89) to rutherfordium (104). If you skip down to the bottom of the table, you can follow the atomic numbers from lanthanum to cerium and from actinium to thorium, and then back up to the main body of the table. Some chemists exclude lanthanum and actinium from the rare earths, considering the lanthanides to start following lanthanum and the actinides to start following actinium. In a way, the rare earths are special transition metals, possessing many of the properties of these elements.
Common Properties of the Rare Earths
These common properties apply to both the lanthanides and actinides.
· The rare earths are silver, silvery-white, or gray metals.
· The metals have a high luster, but tarnish readily in air.
· The metals have high electrical conductivity.
· The rare earths share many common properties. This makes them difficult to separate or even distinguish from each other.
· There are very small differences in solubility and complex formation between the rare earths.
· The rare earth metals naturally occur together in minerals (e.g., monazite is a mixed rare earth phosphate).
· Rare earths are found with non-metals, usually in the 3+ oxidation state. There is little tendency to vary the valence. (Europium also has a valence of 2+ and cerium also a valence of 4+.)
LANTHANIDES
The D Block Elements
The lanthanides are located in block 5d of the periodic table. The first 5d transition element is either lanthanum or lutetium, depending on how you interpret the periodic trends of the elements. Sometimes only the lanthanides, and not the actinides, are classified as rare earths. The lanthanides are not as rare as was once thought; even the scarce rare earths (e.g., europium, lutetium) are more common than the platinum-group metals. Several of the lanthanides form during the fission of uranium and plutonium.
The lanthanides have many scientific and industrial uses. Their compounds are used as catalysts in the production of petroleum and synthetic products. Lanthanides are used in lamps, lasers, magnets, phosphors, motion picture projectors, and X-ray intensifying screens. A pyrophoric mixed rare-earth alloy called Mischmetall (50% Ce, 25% La, 25% other light lanthanides) or misch metal is combined with iron to make flints for cigarette lighters. The addition of <1% Mischmetall or lanthanide silicides improves the strength and workability of low alloy steels.
Common Properties of the Lanthanides
Lanthanides share the following common properties:
· Silvery-white metals that tarnish when exposed to air, forming their oxides.
· Relatively soft metals. Hardness increases somewhat with higher atomic number.
· Moving from left to right across the period (increasing atomic number), the radius of each lanthanide 3+ ion steadily decreases. This is referred to as 'lanthanide contraction'.
· High melting points and boiling points.
· Very reactive.
· React with water to liberate hydrogen (H2), slowly in cold/quickly upon heating. Lanthanides commonly bind to water.
· React with H+ (dilute acid) to release H2 (rapidly at room temperature).
· React in an exothermic reaction with H2.
· Burn easily in air.
· They are strong reducing agents.
· Their compounds are generally ionic.
· At elevated temperatures, many rare earths ignite and burn vigorously.
· Most rare earth compounds are strongly paramagnetic.
· Many rare earth compounds fluoresce strongly under ultraviolet light.
· Lanthanide ions tend to be pale colors, resulting from weak, narrow, forbidden f x f optical transitions.
· The magnetic moments of the lanthanide and iron ions oppose each other.
· The lanthanides react readily with most nonmetals and form binaries on heating with most nonmetals.
ACTINIDES
The F Block Elements
The electronic configurations of the actinides utilize the f sublevel. Depending on your interpretation of the periodicity of the elements, the series begins with actinium, thorium, or even lawrencium. The actinides (An) are prepared by reduction of AnF3 or AnF4 with vapors of Li, Mg, Ca, or Ba at 1100 - 1400°C.
Common Properties of the Actinides
Actinides share the following common properties:
· All are radioactive.
· Actinides are highly electropositive.
· The metals tarnish readily in air.
· Actinides are very dense metals with distinctive structures. Numerous allotropes may be formed (plutonium has at least 6 allotropes!).
· They react with boiling water or dilute acid to release hydrogen gas.
· Actinides combine directly with most nonmetals.
Properties of Element Groups
The alkali metals exhibit many of the physical properties common to metals, although their densities are lower than those of other metals. Alkali metals have one electron in their outer shell, which is loosely bound. This gives them the largest atomic radii of the elements in their respective periods. Their low ionization energies result in their metallic properties and high reactivities. An alkali metal can easily lose its valence electron to form the univalent cation. Alkali metals have low electronegativities. They react readily with nonmetals, particularly halogens.
Summary of Common Properties
· Lower densities than other metals
· One loosely bound valence electron
· Largest atomic radii in their periods
· Low ionization energies
· Low electronegativities
· Highly reactive
Metals
Properties
Metals are shiny solids are room temperature (except mercury), with characteristic high melting points and densities. Many of the properties of metals, including large atomic radius, low ionization energy, and low electronegativity, are due to the fact that the electrons in the valence shell of a metal atoms can be removed easily. One characteristic of metals is their ability to be deformed without breaking. Malleability is the ability of a metal to be hammered into shapes. Ductility is the ability of a metal to be drawn into wire. Because the valence electrons can move freely, metals are good heat conductors and electrical conductors.
Summary of Common Properties
· Shiny 'metallic' appearance
· Solids at room temperature (except mercury)
· High melting points
· High densities
· Large atomic radii
Nonmetals
Properties
Nonmetals have high ionization energies and electronegativities. They are generally poor conductors of heat and electricity. Solid nonmetals are generally brittle, with little or no metallic luster. Most nonmetals have the ability to gain electrons easily. Nonmetals display a wide range of chemical properties and reactivities.
Summary of Common Properties
· High ionization energies
· High electronegativities
· Poor thermal conductors
· Poor electrical conductors
· Brittle solids
· Little or no metallic luster
· Gain electrons easily
Metalloids or Semimetals
Properties
The electronegativities and ionization energies of the metalloids are between those of the metals and nonmetals, so the metalloids exhibit characteristics of both classes. Silicon, for example, possesses a metallic luster, yet it is an inefficient conductor and is brittle. The reactivity of the metalloids depends on the element with which they are reacting. For example, boron acts as a nonmetal when reacting with sodium yet as a metal when reacting with fluorine. The boiling points, melting points, and densities of the metalloids vary widely. The intermediate conductivity of metalloids means they tend to make good semiconductors.
Summary of Common Properties
· Electronegativities between those of metals and nonmetals
· Ionization energies between those of metals and nonmetals
· Possess some characteristics of metals/some of nonmetals
· Reactivity depends on properties of other elements in reaction
· Often make good semiconductors
Alkaline Earth Metals
The alkaline earths possess many of the characteristic properties of metals. Alkaline earths have low electron affinities and low electronegativities. As with the alkali metals, the properties depend on the ease with which electrons are lost. The alkaline earths have two electrons in the outer shell. They have smaller atomic radii than the alkali metals. The two valence electrons are not tightly bound to the nucleus, so the alkaline earths readily lose the electrons to form divalent cations.
Summary of Common Properties
· Two electrons in the outer shell
· Low electron affinities
· Low electronegativities
· Readily form divalent cations.
Transition Metals
Because they possess the properties of metals, the transition elements are also known as the transition metals. These elements are very hard, with high melting points and boiling points. Moving from left to right across the periodic table, the five d orbitals become more filled. The d electrons are loosely bound, which contributes to the high electrical conductivity and malleability of the transition elements. The transition elements have low ionization energies. They exhibit a wide range of oxidation states or positively charged forms. The positive oxidation states allow transition elements to form many different ionic and partially ionic compounds. The formation of complexes causes the d orbitals to split into two energy sublevels, which enables many of the complexes to absorb specific frequencies of light. Thus, the complexes form characteristic colored solutions and compounds. Complexation reactions sometimes enhance the relatively low solubility of some compounds.
Summary of Common Properties
· Low ionization energies
· Positive oxidation states
· Very hard
· High melting points
· High boiling points
· High electrical conductivity
· Malleable
HALOGENS
These reactive nonmetals have seven valence electrons. As a group, halogens exhibit highly variable physical properties. Halogens range from solid (I2) to liquid (Br2) to gaseous (F2 and Cl2) at room temperature. The chemical properties are more uniform. The halogens have very high electronegativities. Fluorine has the highest electronegativity of all elements. The halogens are particularly reactive with the alkali metals and alkaline earths, forming stable ionic crystals.
Summary of Common Properties
· Very high electronegativities
· Seven valence electrons (one short of a stable octet)
· Highly reactive, especially with alkali metals and alkaline earths
NOBLE GASSES
Location on the Periodic Table
The noble gases, also known as the inert gases, are located in Group VIII of the periodic table. Group VIII is sometimes called Group O.
Properties
The noble gases are relatively nonreactive. This is because they have a complete valence shell. They have little tendency to gain or lose electrons. The noble gases have high ionization energies and negligible electronegativities. The noble gases have low boiling points and are all gases at room temperature.
Summary of Common Properties
· Fairly nonreactive
· Complete valence shell
· High ionization energies
· Very low electronegativities
· Low boiling points (all gases at room temperature)
RARE EARTH
The Bottom of the Periodic Table
When you look at the Periodic Table, there is a block of two rows of elements located below the main body of the chart. These elements, plus lanthanum (element 57) and actinium (element 89), are known collectively as the rare earth elements or rare earth metals. Actually, they aren't particularly rare, but prior to 1945, long and tedious processes were required to purify the metals from their oxides. Ion-exchange and solvent extraction processes are used today to quickly produce highly pure, low-cost rare earths, but the old name is still in use. The rare earth metals are found in group 3 of the periodic table, and the 6th (5d electronic configuration) and 7th (5f electronic configuration) periods. There are some arguments for starting the 3rd and 4th transition series with lutetium and lawrencium rather than lanthanum and actinium.
There are two blocks of rare earths, the lanthanide series and the actinide series. Lanthanum and actinium are both located in group IIIB of the table. When you look at the periodic table, notice that the atomic numbers make a jump from lanthanum (57) to hafnium (72) and from actinium (89) to rutherfordium (104). If you skip down to the bottom of the table, you can follow the atomic numbers from lanthanum to cerium and from actinium to thorium, and then back up to the main body of the table. Some chemists exclude lanthanum and actinium from the rare earths, considering the lanthanides to start following lanthanum and the actinides to start following actinium. In a way, the rare earths are special transition metals, possessing many of the properties of these elements.
Common Properties of the Rare Earths
These common properties apply to both the lanthanides and actinides.
· The rare earths are silver, silvery-white, or gray metals.
· The metals have a high luster, but tarnish readily in air.
· The metals have high electrical conductivity.
· The rare earths share many common properties. This makes them difficult to separate or even distinguish from each other.
· There are very small differences in solubility and complex formation between the rare earths.
· The rare earth metals naturally occur together in minerals (e.g., monazite is a mixed rare earth phosphate).
· Rare earths are found with non-metals, usually in the 3+ oxidation state. There is little tendency to vary the valence. (Europium also has a valence of 2+ and cerium also a valence of 4+.)
LANTHANIDES
The D Block Elements
The lanthanides are located in block 5d of the periodic table. The first 5d transition element is either lanthanum or lutetium, depending on how you interpret the periodic trends of the elements. Sometimes only the lanthanides, and not the actinides, are classified as rare earths. The lanthanides are not as rare as was once thought; even the scarce rare earths (e.g., europium, lutetium) are more common than the platinum-group metals. Several of the lanthanides form during the fission of uranium and plutonium.
The lanthanides have many scientific and industrial uses. Their compounds are used as catalysts in the production of petroleum and synthetic products. Lanthanides are used in lamps, lasers, magnets, phosphors, motion picture projectors, and X-ray intensifying screens. A pyrophoric mixed rare-earth alloy called Mischmetall (50% Ce, 25% La, 25% other light lanthanides) or misch metal is combined with iron to make flints for cigarette lighters. The addition of <1% Mischmetall or lanthanide silicides improves the strength and workability of low alloy steels.
Common Properties of the Lanthanides
Lanthanides share the following common properties:
· Silvery-white metals that tarnish when exposed to air, forming their oxides.
· Relatively soft metals. Hardness increases somewhat with higher atomic number.
· Moving from left to right across the period (increasing atomic number), the radius of each lanthanide 3+ ion steadily decreases. This is referred to as 'lanthanide contraction'.
· High melting points and boiling points.
· Very reactive.
· React with water to liberate hydrogen (H2), slowly in cold/quickly upon heating. Lanthanides commonly bind to water.
· React with H+ (dilute acid) to release H2 (rapidly at room temperature).
· React in an exothermic reaction with H2.
· Burn easily in air.
· They are strong reducing agents.
· Their compounds are generally ionic.
· At elevated temperatures, many rare earths ignite and burn vigorously.
· Most rare earth compounds are strongly paramagnetic.
· Many rare earth compounds fluoresce strongly under ultraviolet light.
· Lanthanide ions tend to be pale colors, resulting from weak, narrow, forbidden f x f optical transitions.
· The magnetic moments of the lanthanide and iron ions oppose each other.
· The lanthanides react readily with most nonmetals and form binaries on heating with most nonmetals.
ACTINIDES
The F Block Elements
The electronic configurations of the actinides utilize the f sublevel. Depending on your interpretation of the periodicity of the elements, the series begins with actinium, thorium, or even lawrencium. The actinides (An) are prepared by reduction of AnF3 or AnF4 with vapors of Li, Mg, Ca, or Ba at 1100 - 1400°C.
Common Properties of the Actinides
Actinides share the following common properties:
· All are radioactive.
· Actinides are highly electropositive.
· The metals tarnish readily in air.
· Actinides are very dense metals with distinctive structures. Numerous allotropes may be formed (plutonium has at least 6 allotropes!).
· They react with boiling water or dilute acid to release hydrogen gas.
· Actinides combine directly with most nonmetals.
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