Download Group 1: The Alkali Metals

1 Group 1: The Alkali Metals
Group 1: The Alkali Metals
Alkali metals are the chemical elements found in Group 1 of the periodic table. The
alkali metals include: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (RB),
Cesium (Cs), and Francium (Fr). Hydrogen, while it appears to be listed within
Group 1, is not included in the alkali metals since it rarely exhibits similar behavior.
The word "alkali" received its name from the Arabic word "al qali," meaning "from
ashes". These particular elements were given the name "Alkali" because they react
with water to form hydroxide ions, creating a basic solution (pH>7). Solutions that
have a pH greater than 7 are called alkaline solutions.
Contents
1. Properties and Facts about Alkali Metals
2. Alkali Metal Reactions
3. Trends
4. Flame Colors
5. Elements of the Alkali Metal Group
5.1. Lithium
5.2. Sodium
5.3. Potassium
5.4. Rubidium
5.5. Cesium
5.6. Francium
6. Problems
7. Answers
8. External Video Links
9. Outside Links
10. References
11. Contributors
Properties and Facts about Alkali Metals
Alkali metals are known for being some of the most reactive metals. This is due in
part to their larger atomic radii and low ionization energies. They tend to donate
their electrons in reactions and often have an oxidation state of +1. These metals
are characterized as being extremely soft and silvery in color. They also have low
boiling and melting points and are less dense than most elements. Li, Na, and K
float on water because of their low densities. All of these characteristics can be
attributed to the large atomic radii and weak metallic bonding these elements
possess. Group 1 elements have a valence electron configuration of ns1 and are
good reducing agents (meaning they are easily oxidized).
Alkali Metal Reactions
1) With Hydrogen: all alkali metals react with hydrogen to form hydrides
2K(l) + H2(g) → 2KH(s)
2 Group 1: The Alkali Metals
2) With Water: Alkali metals and water react violently to form strong bases and
hydrogen gas.
General Reaction: 2M(s) + 2H2O → MOH(aq) + H2(g)
where M=alkali metal
example: 2Na(s) + 2H2O → 2NaOH(aq) + H2(g)
note: Reactivity with water increases as you go down the group.
The explosive reaction of sodium with water. In this case, the exothermic reaction is
enough to ignite hydrogen gas.
3) With Halogens: Alkali metals and halogens combine to form ionic salts
General Reaction: M(s) + X(g)→ MX(s)
where M=alkali metal and X=halogen
example: Na+(s) + Cl-(g) → NaCl (s)
4) With Nitrogen: only Lithium reacts with Nitrogen at room temperature
6Li(s) + N2(g) → 2Li3N(s)
5) With Oxygen: Alkali metals form multiple types
of oxides, peroxides and superoxides when combined with oxygen:
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Oxide ion= O2o
compounds generally look like M2O
3 Group 1: The Alkali Metals
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 ex. Li2O
Sodium forms Peroxides
2o Peroxide Ion= O2
 compounds generally look like M2O2
 ex. Na2O2
Potassium, Cesium, and Rubidium form superoxides
o Superoxide ion=O2
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compounds generally look like MO2
 ex. KO2
Trends
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Electronegativity and Ionization energy increase from LEFT TO RIGHT and
BOTTOM TO TOP
o Alkali metals have the lowest electronegativity and ionization energy
o Francium is the least electronegative element.
Atomic radius increases from RIGHT TO LEFT and TOP TO BOTTOM
o Francium is the largest element
Boiling points and melting points increase going BOTTOM TO TOP
o Lithium has the highest boiling point and Francium has the lowest boiling
point in Group 1.
Flame Colors
All alkali metals have their own specific flame color. The colors are caused by the
difference in energy among the valence shell of s and p orbitals, which corresponds
to wavelengths of visible light. When the element is introduced into the flame, its
outer electrons are excited and jump to a higher electron orbital. The electrons then
fall and emit energy in the form of light. The different colors of light depend on how
much energy or how far the electron falls back to a lower energy level. For this
reason, they are often used in fireworks. Each alkali metal has a unique color and is
easily identifiable.
Group 1 Element
Flame Color
Lithium
Crimson
Sodium
Golden Yellow
Potassium
Red/Violet
Rubidium
Blue/Violet
Cesium
Blue/Violet
4 Group 1: The Alkali Metals
Lithium
Sodium
Potassium
Elements of the Alkali Metal Group
Lithium
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named after the Greek word for stone (lithos)
discovered in Sweden in 1817
Atomic number: 3
Atomic weight: 6.941
the lightest and least dense of all alkali metals
highly reactive
a soft metal
has a low ionization energy
Electron configuration: [He]2s1
Often used in rechargeable batteries.
o Includes those used in cell phones, camcorders, laptop computers, and
cardiac pacemakers.
Sodium
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named after the Latin word for soda, Natria
discovered in 1807
Atomic number: 11
Atomic weight: 22.9897
soft silvery metal.
extremely reactive metal
Electron configuration: [Ne]3s1
used in nuclear reactors because of its low boiling point.
Sodium is reacted with chlorine to produce the ionic halide, NaCl
o Sodium chloride is an important part of human diet
 It is used during winter months to control the ice on the road.
5 Group 1: The Alkali Metals
Potassium
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named after the word Potash
o Potash: means that Potassium is an element contained in the compound
discovered in 1807
Atomic number: 19
Atomic Weight: 39.0983
one of the most abundant elements in the earth's crust
oxidizes easily
lavender flame color
Electron configuration: [Ar]4s1
used mostly to produce chemicals, such as fertilizers for use in agriculture.
o Potassium is an important nutrient needed for plant growth.
Rubidium
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named after the Latin word for red, rubidius
Atomic number: 37
soft metal
reddish flame color
Electron configuration: [Kr] 5s1.
discovered in 1861
known to have about 26 isotopes
very large half life at an estimated 49 billion years
Cesium
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Atomic number: 55
forms a strong base with water
Atomic Weight: 132.91
discovered in 1860
often used as a catalyst in various hydrogenation organic reactions
low melting point
Electron configuration: [Xe]6s1.
Francium
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discovered in 1939
very radioactive
hardly any Francium occurring naturally in the earth's crust
Atomic number: 87
Electron configuration: [Rn]6s1
heaviest and most electropositive metal
has the lowest boiling point
o Melts at low temperatures.
most reactive of the alkali metals group
6 Group 1: The Alkali Metals
Problems
1. Which alkali metal has a higher melting point, Sodium (Na) or Francium (Fr)?
Explain.
2. True or False. NH3 is an ionic hydride.
3. What is the electron configuration of Rubidium?
4. Which alkali metals form superoxides?
5. Complete and balance the following equation: Li2O2 + H2O → ?
6. Which element is the most electronegative: Francium, Potassium, or Lithium?
7. True or False: Rubidium has a very short half-life and decays quickly.
8. True or False: All alkali metals react with Nitrogen.
9. Balance the following equation: Li(s)+N2(g)→ ?
10. Compounds that generally look like M2O2 are formed with a metal and what kind
of oxygen ion?.
Answers
1. Sodium has a higher boiling point because it has a larger atomic radius that
Francium. Greater atomic radius means a bigger molecule thus having a higher
boiling point.
2. False. Group 1 and 2 form ionic hydrides. P block forms molecular hydride and
Nitrogen is in P block.
3. [Kr] 5s1
4. K, Rb and Cs.
5. Li2O2 + H2O 2LiOH + H2O2
6. Lithium
7. False
8. False, only Lithium reacts with Nitrogen
9. 6Li(s)+N2(g)→2Li3N(s)
10. Peroxide Ion= O22-
External Video Links
The following website shows the explosive reaction of alkali metals and water. It's
cool stuff! Check it out!
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http://video.google.com/videosearch?hl=en&q=alkali+metals&um=1&ie=UTF8&sa=X&oi=video_result_group&resnum=4&ct=title
http://video.google.com/videoplay?do...66654801392897
Outside Links
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Alexander, M. Dale. "Reactions of the alkali metals with water: A novel
demonstration (TD)." J. Chem. Educ. 1992, 69, 418.
Birmingham, J. F., Jr.; Wood, W. H. "Apparatus for making spectral flames of the
alkali and alkaline earth metals." J. Chem. Educ. 1936, 13, 240.
7 Group 1: The Alkali Metals
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Ciparick, Joseph D.; Jones, Richard F. "A variation on the demonstration of the
properties of the alkali metals (TD)." J. Chem. Educ. 1989,66, 438.
Dye, James L. "Alkali metal anions. An unusual oxidation state." J. Chem.
Educ. 1977, 54, 332.
Nelson, Arthur F. "Potassium soap-soft or hard?" J. Chem. Educ. 1948, 25, 379.
References
1. Fresenius, C. Remigius. Manual Qualitative Chemical Analysis. J. Wiley & Sons,
1897. Page 430
2. Massey, A. G. Main Group Chemistry. London: Ellis Horwodd, 1990. Print.
3. Petrucci et al., General Chemistry, Principles & Modern Applications, by
Macmillan Publishing Company,Ninth Edition,Page 877.
Contributors
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Kellie Berman, Nilshita Devi