Section 7.7Group Trends for the

Active MetalsLouis WilkersonAndrew KatsmanMichael Levin

Overview• Group 1A: The Alkali Metals– Basic characteristics– Chemical Reactions Involving Alkali Metals– Interesting Facts

• Group 2A: The Alkaline Earth Metals– Basic characteristics– Chemical Reactions Involving Alkali Metals– Interesting Facts

• Outside the Class

Group 1A: The Alkali MetalsCharacteristics

• Soft metallic solids w/ silvery luster• High thermal and electrical

conductivities• Very reactive• Pattern: melting points decrease,

first ionization energies decrease, and densities increase with the increase of the atomic radius

• Exist in nature only as compounds• Combine directly with most

nonmetals – (ex: Hydrogen and Sulfur)

Melting Pt (oC) | Density (g/cm2)

181 0.53

98 0.97

63 0.86

39 1.53

28 1.88

Group 1A: The Alkali MetalsChemical Reactions

• Hydrides:– 2M (s) + H2(g) 2MH(s)

• Form hydrides In hydrides of alkali metals, hydrogen is present as H –

(hydride ion)• Sulfides

– 2m(s) + S(s) M2S(s)

• Form sulfides• Water

– 2M(s) + 2H2O(l) 2MOH(aq) + H2(g)

• Vigorous reaction, very exothermic• Heavier the metal, the more violent

the reaction

Reaction of Potassium and Water

Group 1A: The Alkali MetalsChemical Reactions

(Continued)• Oxygen (most complex)– Lithium is the exception (reacts normally with O2 –)– Sodium (Na) is the only alkali metal that forms metal

peroxides , containing the O22- ion

• Reaction: 2Na(s) + O2(g) Na2O2(s)

– Potassium (K), Rubidium(Rb), and Cesium (Cs) react with Oxygen to form metal superoxides, containing the O2

- ion

• Ex: K(s) + O2(g) KO2(s)

Group 1A: The Alkali MetalsInteresting Facts

• Alkali metals emit characteristic colors when placed in a flame– The high temperature of the flame

electronically excites valence electron– Atom emits energy in the form of visible

light as it returns to its ground state• Sodium:

– Table salt– Human Diet

• Lithium’s most-know or best purpose is a medication for people with bipolar disorder– THIS DOES NOT MEAN YOU SHOULD LICK A

LITHIUM BATTERY TO CALM YOURSELF!• People have actually tried this

Potassium

Lithium

Alkali Metal Questions

Predict the reactions of the following with oxygen

1.Lithium 2.Sodium3.Cesium

Alkali Metal Answers

1. 4Li(s) + O2(g) 2Li2O(s)

2. 2Na(s) + O2(g) Na2O2(s)

3. Cs(s) + O2(g) RbO2 (s)

Group 2A: The Alkaline Earth MetalsCharacteristics

• Have typical metallic properties • Alkaline Earth metals are harder and more dense

than the Alkali metals• Melt at higher temperatures than Alkali metals• Do not have a distinct Periodic-Table-pattern• Also, these are less reactive than the Alkali

metals– Beryllium (Be) and Magnesium (Mg) are the least

reactive of all the Alkaline Earth metals

Group 2A: The Alkaline Earth MetalsChemical Reactions

• Trend of increasing reactivity within the Alkaline Earth Metals (Beryllium and Magnesium least, Strontium and Barium most)– Shown by behavior of elements towards H2O (l and g)

• Beryllium doesn’t react with water or steam, for example• Magnesium doesn’t react with water, but does react with steam

– Mg(s) + H2O (g) MgO(s) + H2 (g)– Calcium and elements below react readily with water at room

temperature• However, more slow than alkali metals adjacent to them• Produce the metal hydroxide and H2

• Ex: Ca(s) + 2H2O(l) Ca(OH)2 (aq) + H2(g)

Group 2A: The Alkaline Earth MetalsChemical Reactions (Continued)

• In Alkaline Earth metals, it is important to note that they have the tendency to lose their two outer s sublevel electrons in order to form 2+ ions– Example:• Mg 2+(s) + Cl2

1- (g) MgCl2(s)

Group 2A: The Alkaline Earth MetalsInteresting Facts

• Like the Alkali metals, Alkaline Earth metal ions give off characteristic colors when strongly heated in a flame

• Both Magnesium and Calcium are used in:– Building and other structural applications– Dietary supplements– The metabolism of living things (including humans)

• Barium and Beryllium are very useful, for they are used in the areas of both medicine and jewelry, among other things

• Strontium’s most known or basic use is in fireworks

Strontium

Barium

Alkaline Earth Metal Questions

1. Why is calcium generally more reactive than magnesium?

2. Why is calcium generally less reactive than potassium?

Alkaline Earth Metal Answers

1. Why is calcium generally more reactive than magnesium?– As proved by the basic behaviors of alkaline earth

metals with water, magnesium will only react only with steam. Calcium, however, reacts with both steam AND water.

2. Why is calcium generally less reactive than potassium?– Potassium has less valence electrons than calcium

does. Thus, potassium is “more willing” to react than calcium. Also, alkaline earth metals are generally less reactive than their alkali metal counterparts.

Outside the Class

• Explosive Stuff (Alkali Metals):• http://video.google.com/videoplay?docid=-21

34266654801392897&ei=bfr2SsT1FoLIqQLzuLXhBg&q=alkali+metals&hl=en#

• Lithium in 7 Up…

Works Cited• “Alkali Metals.” Science Clarified. N.p., n.d. Web. 7 Nov. 2009.

<http://www.scienceclarified.com/ everyday/ Real-Life-Chemistry-Vol-1/ Alkali-Metals.html>.

• "Alkaline Earth Metals." Science Clarified. N.p., n.d. Web. 7 Nov. 2009. <http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol- 1/ Alkaline-Earth-Metals.html>.

• Brown, Theodore L., H. Eugene LeMay, Jr., and Bruce E. Bursten. “Chapter 7: Periodic Properties of the Elements.” Chemistry: The Central Science. 9th ed. Upper Saddle River, New Jersey: Prentice Hall, 2003. 236 - 273. Print.

• “Periodic Table: Alkali Metals.” ChemicalElements.com. N.p., n.d. Web. 7 Nov. 2009. <http://www.chemicalelements.com/ groups/

alkali.html>.