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Topic 10: Elements

Table of ContentsTable of ContentsTopic 10Topic 10

Basic Concepts

Additional Concepts


• An element’s chemical and physical properties are closely related to its position in the periodic table and that certain properties repeat periodically.

Periodic Properties of the Elements

Elements: Basic ConceptsElements: Basic ConceptsElements: Basic ConceptsElements: Basic Concepts

• Both position in the periodic table and the properties of the elements arise from the electron configurations of their atoms.

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• Understanding the relationship between electron configuration and position in the periodic table enables you to predict the properties of the elements and the outcome of many chemical reactions.

Periodic Properties of the Elements

Elements: Basic ConceptsElements: Basic ConceptsElements: Basic ConceptsElements: Basic ConceptsTopic 10Topic 10


• Elements in the same group (vertical column) of the periodic table have the same number of valence electrons, and because of this, they have similar properties.

Behavior of Main Group Elements

• But elements in a period (horizontal row) have properties different from one another.




• As a result, the character of the elements changes.

• This is because the number of valence electrons increases from one to eight as you move from left to right in any row of the periodic table except the first.




• Each period begins with two or more metallic elements, which are followed by one or two metalloids.

• The metalloids are followed by nonmetallic elements, and every period ends with a noble gas.



Trends in Metallic Properties



Patterns in Atomic Size • Recall that the size of an atom increases in

any group of elements as you go down the column because the valence electrons are found in energy levels farther and farther from the nucleus.

• But how does atomic radius change across a period from left to right?

• The lithium atom, with only three electrons, is actually larger than the fluorine atom, which has nine.



Patterns in Atomic Size • There’s a simple explanation for the trend of

decreasing atomic size across a period.

• The lithium nucleus has three protons, so there’s an attractive force of 3+ acting on the electron.

• Picture the valance electron on a lithium atom.



Patterns in Atomic Size

• Now, think about the valence electrons in a beryllium atom.

• Here, there is an attractive force of 4+ from the four protons in the beryllium nucleus.



Patterns in Atomic Size

• With each increase in nuclear charge across the period, the outer electrons are attracted more strongly toward the nucleus, resulting in smaller size.



Atomic Radii of Main Group Elements



Ionic Size

• Atomic size is an important factor in the chemical reactivity of an element.

• Ionic size is also important in determining how ions behave in solution and the structure of solid ionic compounds.



Ionic Size

• When metallic atoms lose one or more electrons to become positive ions, they acquire the configuration of the noble gas in the preceding period.

• This means that the outermost electrons of the ion are in a lower energy level than the valence electrons of the neutral atom.



Size of Atoms and Their Ions

• The electrons that are not lost by the atom experience a greater attraction to the nucleus and pull together in a tighter bundle with a smaller radius.

• The result is that all positive ions have smaller radii than their corresponding atoms.




• When an atom gains electrons to become a negative ion, the atom acquires the electron configuration of the noble gas at the end of its period.

• But the nuclear charge doesn’t increase with the number of electrons.




• In the case of fluorine, a nuclear charge of 9+ must hold ten electrons in the F– ion.

• The result is that all the electrons are held less tightly, and the radius of the ion is larger than the neutral atom.



Patterns in Ionic Radii― The Alkali Metals

• The Group 1 elements—lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr)—are called the alkali metals. The alkali elements are soft, silvery-white metals and good conductors of heat and electricity.


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Patterns in Ionic Radii― The Alkali Metals

• Their chemistry is relatively uncomplicated; they lose their s valence electron and form a 1+ ion with the stable electron configuration of the noble gas in the preceding period.



Patterns in Ionic Radii― The Alkaline Earth Metals

• The Group 2 elements—beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra)—are called the alkaline earth metals.



Patterns in Ionic Radii― The Alkaline Earth Metals

• The properties of Group 2 elements are similar to those of the Group 1 elements.

• Like the alkali metals, they are too reactive to be found as free elements in nature.

• They lose both of their s valence electrons and form 2+ ions with the stable electron configuration of the noble gas in the preceding period.



Important Properties of Magnesium

• Alloys of magnesium are used where light weight and strength are important, as in this jet engine.

• Magnesium resists corrosion because it reacts with oxygen in the air to form a coating of magnesium oxide.

• The coating of MgO protects the metal underneath from further reaction with oxygen.



Strontium Reveals Its Presence

• Strontium is a less well-known element of Group 2, but it’s important, nevertheless.

• Because of its chemical similarity to calcium, strontium can replace calcium in the hydroxyapatite of bones and form Sr5(PO4)3OH.



Strontium Reveals Its Presence

• This could be a problem only if the strontium atoms are the radioactive isotope strontium-90, which is hazardous if it is incorporated into a person’s bones.



Group 13 Elements

• Only boron, the first element in Group 13, is a metalloid.

• The other Group 13 elements—aluminum (Al), gallium (Ga), indium (In), and thallium (Tl)—are metals.



Group 13 Elements

• None of the metals are as active as the metals in Groups 1 and 2, but they’re good conductors of heat and electricity.



The Uses of Group 13 Elements

• Boron is a metalloid found in boric acid (H3BO3) and borax (Na2B4O7•10H2O).

• Boric acid is one of the active ingredients in eyewash or contact lens-cleaning solution.

• Borax is the abrasive in some tough cleansing powders.

• It’s also used as a water softener and is an important component in some types of glass.



Group 14 Elements

• The Group 14 elements—carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb)—exhibit a variety of properties.



Group 14 Elements

• Carbon is a nonmetal, silicon and germanium are metalloids, and tin and lead are metals.



Group 15 Elements

• The trend in metallic properties is obvious as you go from the top of Group 15 to the bottom—from nitrogen (N) to phosphorus (P) to arsenic (As) to antimony (Sb) and bismuth (Bi).

• Nitrogen and phosphorus are nonmetals.



Group 15 Elements

• They form covalent bonds to complete their outer-level configuration.

• Arsenic and antimony are metalloids and either gain or share electrons to complete their octets.

• Bismuth is more metallic and often loses electrons.



Group 16 Elements

• The Group 16 elements—oxygen (O), sulfur (S), selenium (Se), and tellurium (Te)—are nonmetals, and polonium (Po) is a metalloid.

• Their valence-electron configuration is s2p4.

• With rare exceptions, oxygen gains two electrons and forms the oxide ion (O2–) with the neon configuration.



Group 16 Elements

• Oxygen reacts with both metals and nonmetals and, among the nonmetals, is second only to fluorine in chemical reactivity.



Group 17 Elements• The halogens—fluorine (F), chlorine (Cl),

bromine (Br), idodine (I), and astatine (At)—are active nonmetals.

• Because of their chemical reactivity, they don’t exist as free elements in nature.



Group 17 Elements

• Their chemical behavior is characterized by a tendency to gain one electron to complete their s2p5 valence-electron configuration and form a 1– ion with a noble-gas configuration.



Group 18 Elements

• Helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), the noble gases, were originally called the inert gases because chemists couldn’t get them to react.



Properties of the Transition Elements• With the exception of the Group 12 elements

(zinc, cadmium, and mercury), the transition metals have higher melting points and boiling points than those of almost all of the main group elements.



Properties of the Transition Elements• Multiple oxidation states are characteristic of

the transition elements. • Many of the transition elements can have

multiple oxidation numbers ranging from 2+ to 7+.



Properties of the Transition Elements

• These oxidation numbers are due to involvement of the d electrons in chemical bonding.



Lanthanides and Actinides: The Inner Transition Elements

• In the lanthanides, electrons of highest energy are in the 4f sublevel.


• The lanthanides were once called rare earth elements because all of these elements occurred in Earth’scrust as earths, an older term for oxides, and seemed to be relatively rare.


Lanthanides and Actinides: The Inner Transition Elements

• The highest-energy electrons in the actinides are in the 5f sublevel.



Basic Assessment QuestionsBasic Assessment Questions

Explain why elements within the same group of the periodic table are similar but not identical in properties, such as ionization energy.

Question 1 Topic 10Topic 10


Elements within the same group of the periodic table have the same number of valence electrons, but different numbers of nonvalence electrons.

Answer

Basic Assessment QuestionsBasic Assessment QuestionsTopic 10Topic 10


Compare the alkali and alkaline earth metals in terms of position in the periodic table, number of valence electrons, and overall properties.

Question 2




Answer

The alkali metals have one valence electron and are in group 1A. The alkaline earth metals have two valence electrons and are in group 2A. Both types of metals are reactive, but the alkaline earth metals are less reactive. The alkali metals are softer.

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Compare the metallic character of the elements carbon, silicon, and lead. What do these elements have in common in terms of valance electrons and placement in the periodic table?

Question 3




Answer

Carbon is a nonmetal, silicon is a metalloid, and lead is a metal. All have four valence electrons and are located in group 4A.

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Elements: Additional ConceptsElements: Additional Concepts Elements: Additional ConceptsElements: Additional Concepts Topic 10Topic 10

Additional Concepts


Reactivity of the Group 1A Element, Lithium

Elements: Additional ConceptsElements: Additional Concepts Elements: Additional ConceptsElements: Additional Concepts

• Lithium is the most active metal in the second period because it can attain the noble-gas configuration of helium by losing a single electron.

• If lithium loses one electron from its 2s sublevel, its electron configuration changes from 1s22s1 to 1s2.

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• The resulting lithium ion has a 1+ charge and the same electron configuration as a helium atom.

• While this is not an octet, it is a noble-gas configuration.

• Elements tend to react in ways that allow them to achieve the configuration of the nearest noble gas.

Reactivity of the Group 1A Element, Lithium



Reactivity of the Group 2A Element, Beryllium

• Beryllium, the next element in the second period, must lose a pair of 2s electrons to acquire the helium configuration.

• It’s harder to lose two electrons than it is to lose one, so beryllium is slightly less reactive than lithium.

• Nevertheless, beryllium does react by losing both of its 2s electrons and forming a 2+ ion with the helium electron configuration.



Reactivity of the Group 3A Element, Boron

• If this pattern continued, you would expect boron to lose three electrons to attain the helium configuration.

• Sometimes, boron does react by losing electrons, but often it reacts by sharing electrons.

• Boron is the only metalloid in the period.



• That means boron sometimes behaves like a metal and loses electrons like its neighboring metals, lithium and beryllium.

• When it loses electrons, boron achieves the noble-gas configuration of helium.




• But more often, boron acts like a nonmetal and shares electrons.

• Boron is unusual because it has only three electrons to share and cannot acquire an octet of electrons by just sharing.




Reactivity of the Group 4A, 5A, 6A, and 7A Elements, C, N, O, and F

• Carbon, nitrogen, oxygen, and fluorine are nonmetals.

• Carbon, with the configuration [He]2s22p2, and nitrogen, with the configuration [He]2s22p3, share electrons to attain the noble-gas configuration of neon, [He]2s22p6.



Reactivity of the Group 4A, 5A, 6A, and 7A Elements, C, N, O, and F

• Oxygen, with the configuration [He]2s22p4, gains two electrons to form the oxide ion, O2–.

• Fluorine, with the configuration [He]2s22p5, gains one electron to become the fluoride ion, F–.



Reactivity of the Group 1A Elements:The Alkali Metals

• Because of their chemical reactivity, the alkali metals don’t exist as free elements in nature.


• Sodium, for example, is found mostly combined with chlorine in sodium chloride.

Click box to view movie clip.


Reactivity of the Group 1A Elements:The Alkali Metals

• Metallic sodium is obtained from NaCl through a process called electrolysis in which an electric current is passed through the molten salt.



Spontaneous Reactivity• Sodium and the other Group 1

elements are among the most active of all the metals.

• All Group 1 metals react vigorously with water.

• When they do, they replace hydrogen and form a hydroxide, as shown in the following equation.



Alkali Metals Form Hydroxides• So much heat is generated in the rapid reaction

of potassium and water that the hydrogen gas produced in the reaction bursts into flames.


• Potassium hydroxide (KOH) formed in the reaction makes the solution alkaline. Hydroxides are important household and industrial chemicals.


Household, Industrial, and Biological Uses

• Sodium hydroxide is used in the digestion of pulp in the process of making paper.


• It’s also used in making soap, in petroleum refining, in the reclaiming of rubber, and in the manufacture of rayon.


• Compounds of sodium and potassium are important to the human body because they supply the positive ions that play a key role in transmitting nerve impulses that control muscle functions.



• It is sodium hydroxide’s ability to convert fats to soap that makes it effective as a kitchen drain cleaner.


• It’s one of the three major components of fertilizers; the other two are also main group elements—nitrogen and phosphorus.



• Potassium is also an essential nutrient for plants.


Reactivity of the Group 2A Elements, the Alkaline Earth Metals

• The most reactive element in the alkaline earth group is the one with the largest atomic radius and, therefore, the least attraction for its two valence electrons.

• Knowing this, you can predict that radium, the largest atom in the group, is the most reactive.



Reactivity of the Group 2A Elements, the Alkaline Earth Metals

• The trend to increasing reactivity with increasing size of atom for the alkaline earth metals is illustrated by the reaction of the elements with water.



Reactions of Magnesium and Calcium• Magnesium oxide is also formed when

magnesium is heated in air.

• It burns vigorously, producing a brilliant white light and magnesium oxide.

• In the process, magnesium loses two electrons to form the Mg2+ ion, and oxygen gains two electrons to form the O2– ion.



Reactions of Magnesium and Calcium• Together, they form the ionic compound MgO.

• The following equation shows what happens.



Reactions of Strontium

• Strontium makes its presence known by the brilliant red color of a fireworks display.

• The red color also identifies strontium in laboratory flame tests.



Reactivity of the Group 13 Elements: The Importance of Aluminum

• Because aluminum is neither as hard nor as strong as steel, it is often alloyed with other metals to make structural materials.

• Aluminum alloys are used in automobile engines, airplanes, and truck bodies where high strength and light weight are important.



Aluminum in Your Home

• At home, you may find bicycles, outdoor furniture, ladders, and pots and pans that are made of aluminum or an aluminum alloy.



Aluminum as a Conductor• Even though aluminum doesn’t conduct

electricity as well as copper, it costs less to use aluminum than copper for transmission of electricity.

• Aluminum cables are much lighter than copper cables, so fewer support towers are needed to hold the miles and miles of cable that span the country.



Gallium’s Low Melting Point• Gallium, indium, and thallium react much

like aluminum. • But gallium,

shown here, has an unusually low melting point, 29.8°C.

• The heat of a hand is sufficient to liquefy the metal. For comparison, aluminum melts at 660ºC.



Reactivity of the Group 14 Elements: Silicon

• Silicon, like boron, is a metalloid.

• It occurs in sand as silicon dioxide, SiO2—sometimes called silica.

• About 59 percent of Earth’s crust is made up of silica.

• In its elemental form, silicon is a hard, gray solid with a relatively high melting point, 1410ºC.



• Silicon is in window glass and in the chips that run computers.

• Compounds of silicon are found in lubricants, caulking, and sealants.

Reactivity of the Group 14 Elements: Silicon



Special Glasses from Silicon

• Silicon is important in semiconductors.

• It’s also important in making alloys and in ceramics, glass, and cement.

• The glass-ceramic shown here doesn’t expand when heated so it won’t break when exposed to large temperature changes.



“Tin” Cans and Alloys

• Tin (Sn) is best known for its use as a protective coating for steel cans used for food storage.

• The coating protects the steel from corrosion.



“Tin” Cans and Alloys

• Tin is also a principal component in the alloys bronze, solder, and pewter.

• Tin is a soft metal that can be rolled into thin sheets of foil.



The Lead-Acid Storage Battery• Lead (Pb) has been known and used since

ancient times. • It’s obtained from the ore galena (PbS). • Lead is alloyed with tin in solder and

cheaper grades of pewter. • The most important

use of lead is in the lead-acid storage batteries used in automobiles.



Reactivity of the Group 15 Elements

• Nitrogen, as the chemically unreactive molecule N2, makes up 78 percent by volume of Earth’s atmosphere.

• Plants and animals can’t use nitrogen in this form.

• Lichens, soil bacteria, and bacteria in the root nodules of beans, clover and other similar plants convert nitrogen to ammonia and nitrate compounds.




• Lightning also converts atmospheric nitrogen to nitrogen monoxide (NO).

• Plants use these simple nitrogen compounds to make proteins and other complex nitrogen compounds that become part of the food chain.



Ammonia, the Essential Fertilizer

• Ammonia is used as a liquid fertilizer applied directly to soil, or it can be converted to solid fertilizers such as ammonium nitrate, NH4NO3; ammonium sulfate, (NH4)2SO4; or ammonium hydrogen phosphate, (NH4)2HPO4.



Two Allotropes of Phosphorus• White and red phosphorus are two common

allotropes of phosphorus.

• Notice that the white phosphorus is photographed under a liquid because this form of phosphorus, which has the formula P4 reacts spontaneously with oxygen in the air.



Two Allotropes of Phosphorus

• Red phosphorus is used in making matches.



Gallium Arsenide Semiconductors• Arsenic is a metalloid found widely

distributed in Earth’s crust. • An increasingly important use of the element

is in the form of the binary compound gallium arsenide, GaAs.

• Because of its higher speed and performance, gallium arsenide is now replacing silicon in some of its semi-conductor applications in electronic circuitry.



Antimony

• Antimony (Sb) is used primarily in alloys with other materials, particularly lead.

• Antimony improves the hardness and corrosion resistance of the metal.




• Like oxygen, sulfur gains two electrons and forms the sulfide ion (S2–) when it reacts with metals or with hydrogen.

• But in its reactions with nonmetals, sulfur can have other oxidation numbers.

• Much of the sulfur produced in the United States is taken from deposits of elemental sulfur by the Frasch process of mining.



Unstable Hydrogen Peroxide

• In your household chemical storehouse, you’ll find oxygen in solutions of hydrogen peroxide (H2O2), shown in a brown bottle.



An Application of Selenium’s Photosensitivity

• The chemistry of selenium and tellurium is similar to that of sulfur.

• Selenium has the property of increased electrical conductivity when exposed to light.

• This property has applications in security devices and mechanical opening and closing devices, where the interruption of a beam of light triggers an electrical response.



Fluorides Prevent Tooth Decay• Many towns and cities add fluorides to their

water supply, and sodium fluoride (NaF) or tin(II) fluoride (SnF2) is often added to toothpastes to prevent tooth decay.



Silver Bromide Coats Photographic Film

• The compound of the halogens are more important than the free elements.

• Compounds of chlorine with carbon, such as carbon tetrachloride and chloroform, are important solvents.

• Silver bromide (AgBr) is important in the light-sensitive coating on film.



Reactivity of Group 18 Elements, Noble Gases

• The lack of reactivity of noble gases is understandable; all the noble gases have a full complement of valence electrons and of noble gasses, therefore, no tendency to gain or lose electrons.



Reactivity of the Group 3-12 Elements, Transition Elements: Iron

• Besides its importance as a structural metal, iron is an essential element in biological systems.

• It is the iron ion at the center of the heme molecule that binds oxygen.



Chromium• When chromium is alloyed with iron, tough,

hard steels or steels that are corrosion-resistant are formed.

• Chromium is also alloyed with other transition metals to produce structural alloys for use in jet engines that must withstand high temperatures.

• A self-protective metal, chromium is often plated onto other materials to protect them from corrosion.



Zinc

• Like chromium, zinc is a corrosion-resistant metal.

• One of its principal uses is as a coating on iron and steel surfaces to prevent rusting.

• In the process called galvanizing, a surface coating of zinc is applied to iron by dipping the iron into molten zinc.



Zinc

• Zinc is also important when alloyed with other metals.

• The most important of these alloys is the combination of zinc with copper in brass.



Reactivity of Lanthanides and Actinides: Cerium

• Misch metal is 50 percent cerium combined with lanthanum, neodymium, and a small amount of iron.

• Cerium is the principal metal in the alloy called misch metal.



Other Lanthanides

• Neodymium (Nd) is used not only to decolorize glass but to add color to glass.

• Other lanthanides are used in the glass industry.

• When added to the glass used for welders’ goggles, neodymium and praseodymium (Pr) absorb the eye-damaging radiation from welding.



Radioactivity and the Actinides

• Uranium (U) is a naturally occurring, radioactive element used as a source of nuclear fuel and other radioactive elements.

• Plutonium (Pu) is one of the elements obtained from the use of uranium as a nuclear fuel.



Radioactivity and the Actinides

• Some actinides have medical applications: for example, radioactive californium-252 (Cf) is used in cancer therapy.

• Better results in killing cancer cells have been achieved using this isotope of californium than by sing the more traditional X-ray radiation.



Additional Assessment QuestionsAdditional Assessment Questions

Name the elements in the following pair. Compare them in terms of group number, number of valence electrons, and metallic character.

Question 1

As and Bi

Topic 10Topic 10


As: arsenic; 5A; 3; metalloid

Answers

Bi: bismuth; 5A; 5; metal

Additional Assessment QuestionsAdditional Assessment QuestionsTopic 10Topic 10


State a use for each element.

Question 2

A. Se and Cl

B. I and H

C. S and F



AnswersA. Se: used in solar panels and photcopiers Cl: used as a bleach and disinfectant and to make certain plastics

B. I: silver compound used to coat photographic film He: used in balloons and by divers

C. S: used to make sulfuric acid F: used in toothpaste to protect tooth enamel



An element is metallic and radioactive. It has six valence electrons. Identify the element’s group number and name the element.

Question 3



Answer

Group 6A, polonium



Compare the period-2 elements that are in groups 5A, 6A, 7A, and 8A in terms of number of valence electrons and reactivity.

Question 4



Nitrogen (group 5A) has five valence electrons and is relatively unreactive.

Answers

Neon (group 8A) has eight valence electrons and is extremely unreactive.

Fluorine (group 7A) has seven valence electrons and is extremely reactive.

Oxygen (group 6A) has six valence electrons and is reactive.



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