1	M4 Periodic Table III: Group 1 & 2 Metals
2	Learning objectives Concepts: Group 1, alkali metal, halogen, melting point, boiling point, trend (pattern) reaction, displacement, reactivity, acidic, basic, metallic, nonmetallic Skills: Describe and explain trends for group 1 and 2 in their appearance, melting point, density, and their reaction with water Predict properties of other elements in the group given data where appropriate Identify and describe displacement reactions between metals and water Describe and explain the change in reactivity of metals in period 3 (sodium, magnesium and aluminum).
3	Group 1 Metals The elements that appear in the first column of the periodic table are referred to as Group 1 metals. They are also called Alkali metals.
4	Group 1 Metals If you remember, they all have 1 electron in the valence shell of their atoms. Because of this, they have similar physical and chemical properties. But their atoms contain different number of shells in their atoms. Therefore, they show a trend in their physical and chemical properties. In general they are soft, have low boiling point and, chemically, are very very reactive.
5	Some General Properties of Metals Physical Properties They are usually shiny. However they may look dull if they they are covered in a layer of metal oxide. All metals will conduct electricity. All metals are good conductors of heat Most metals are malleable: they can be beaten into different shapes Many metals like copper are ductile: they can be stretched into thin wires Most metals have high melting points and boiling points
6	Group 1: The Alkali metals Sodium metal is so reactive that it is stored under kerosene or medicinal oil to protect it from the oxygen in the air.
7	ALL Group 1 Alkali metals have: Similar physical properties: LOW melting points and LOW boiling points Low compared to other metals: From solid to liquid From liquid to gas Lithium 180 ⁰C 1342 ⁰C Sodium 98 ⁰C 883 ⁰C Potassium 63 ⁰C 760 ⁰C Whereas, Copper 1100 ⁰C 2567 ⁰C Iron 1500 ⁰C 2750 ⁰C
8	ALL Group 1 Alkali metals are: Soft, can be easily cut with a knife: A physical property
9	Cutting
10	Cutting But, we can apply a force to make the atoms move apart from each other.
11	Cutting What does this tell us about the forces between the atoms of Lithium (Sodium and Potassium) that holds them all together? Are the forces between the Lithium atoms WEAK or STRONG? Which metal has the stronger forces between its atoms Potassium or Copper? How would you test this – what do you predict would happen?
12	Similarities in Chemical reactivity of Group 1 Metals The reason the elements in group 1 display similar chemical properties is that they have 1 electron in their valence shell. Their chemical behavior therefore is dominated by the loss of their single outer electron: M ® M⁺ + e^- where M = an alkali metal Therefore, they show similarities in their reaction with other substances (such as air, water etc.). In other words, they form similar products. However, the speed and vigor with which they react with other substances is different. Let’s first look at their reaction with water which can be classified as a displacement reaction.
13	Displacement (reactions): An Introduction The reaction between group 1 metals and water can be classified as a displacement reaction. To displace: to kick something out and take its place.
14	Displacement The South Park Way Cartman and Stan are good friends…well most of the time…except when it comes to the question of who gets to play with piggy.
15	Displacement of Stan One fine morning, Stan is happily placing with piggy…
16	Displacement of Stan And as everyone knows, Cartman gets what he wants.
17	Displacement of Stan
18	Displacement of Stan: The equation
19	Displacement of Hydrogen Lithium + water à lithium hydroxide + hydrogen
20	Similarity & Trend Reactivity INCREASES as we move down the group. 1. ALL alkali metals react with water to form their hydroxide and hydrogen gas: 2Li₍_s₎ + 2H₂O₍_l₎ ® 2LiOH₍_aq₎ + H₂₍_g₎ 2Na₍_s₎ + 2H₂O₍_l₎ ® 2NaOH₍_aq₎ + H₂₍_g₎ 2K₍_s₎ + 2H₂O₍_l₎ ® 2KOH₍_aq₎ + H₂₍_g₎ In general: 2M₍_s₎ + 2H₂O₍_l₎ ® 2MOH₍_aq₎ + H₂₍_g₎ Where M = group 1 metal. Notice the formula of the hydroxide is similar.
21	Reaction with water The reaction is more and more violent down the group. While lithium reacts quietly with water, sodium darts about making a fizzing sound and at the end may produce a pop sound when the hydrogen catches on fire. Potassium when introduced into the water produces a burning flame (see picture). The gas produced can be identified as hydrogen by testing it with a lit splint. When a lit splint is applied to the mouth of a test tube containing hydrogen, it burns with a characteristic ‘pop’ sound.
22	Similarity & Trend 2. All alkali metals on exposure react with air to produce their corresponding oxide (combination reaction). 2Li₍_s₎ + O₂ ₍_g₎® Li₂O₍_s₎ 2Na₍_s₎ + O₂ ₍_g₎® Na₂O₍_s₎ In general 2M₍_s₎ + O₂ ₍_g₎® M₂O₍_s₎ Again, notice that the formula of the oxide is similar. 3. All alkali metals react readily with group 7 elements (halogens) to produce their corresponding halide, compound of group 7 element. 2Na₍_s₎ + Cl₂ ₍_g₎ ® 2NaCl₍_s₎ 2K₍_s₎ + Br₂ ₍_l₎ ® 2KBr₍_s₎ In general 2M₍_s₎ + X₂ ₍_{g or l or s}₎ ® 2MX₍_s₎
23	Summary So, they exhibit similar chemical properties: They all react with oxygen when exposed to air. They all react with water to produce the hydroxide and hydrogen gas. They all react with halogens to produce halides. They exhibit a trend in their reactivity: Reaction gets more vigorous going from Lithium to Francium. In other words, reactivity increases going down the group. Why? Before we answer that questions, first why it is that elements react with each other in the first place.
24	Reaction & Energetic Stability Elements react with other elements because they are energetically unstable. Atoms of noble gases are energetically stable while the rest of the elements in the periodic table are not. Atoms of noble gases are energetically stable because their valence shells contain the maximum number of electrons that they can accommodate. So, atoms of other elements try to attain a similar electronic structure as those of noble gases and they do so by reacting with other elements. In order to achieve the same electronic structure as a noble gas, group 1 metals have two options gain 7 electrons and become like the noble gas in their own period, or lose 1 electron and become like the noble gas in the period above them.
25	Conversion of Lithium Which one do you think would be easier—gaining 7 electrons or losing 1 electron to look like a noble gas?
26	Conversion of Sodium Which one do you think would be easier—gaining 7 electrons or losing 1 electron?
27	Which one? Potassium also could either gain 7 electrons (and become like the atom of Krypton) or lose 1 electron (and become like the atom of Argon). What does happen with the atoms of the first group elements when they react with another substance is that they lose 1 electron instead of gaining 7. They lose 1 electron for the simple reason that it is easier than gaining 7. Now, what about the explanation for the increasing trend going down the group?
28	Alkali metals Trends in Reactivity Going Down Group 1 reactivity increases.
29	Reactivity Trend: Reason Therefore, going Down Group 1 EASIER to LOSE OUTER ELECTRON So MORE CHEMICALLY REACTIVE That is, it is easier for K to lose an electron than it is for Na. And it is easier for Na to lose an electron than it is for Li. K is more reactive than Na. Na is more reactive than Li. Reactivity increases going down the group of group 1 metals.
30	Summary Going Down Group 1 Bigger atoms one extra full shell of electrons for each period you go down. Therefore, Softer (easier to cut) Lower melting point Lower boiling point, because of weakening force of attraction between atoms. And more reactive Because the outer electron is more easily lost as it is farther away from the nucleus.
31	Group 2 Metals Next to the alkali metals are the alkaline earth metals. If you remember, they all have 2 electron in the valence shell of their atoms. Again, because of this, they have similar physical and chemical properties. Their atoms of course contain different number of shells in their atoms. Therefore, they also show a trend in their physical and chemical properties.
32	Group 2 Metals An Alkaline earth metal are denser and harder and has a higher melting point than the alkali metal in the same period. Alkaline earth metals are reactive, but not as reactive as the alkali metals.
33	Reaction of Group 2 Metals with Water When calcium, for instance, reacts with water, it’s not as vigorous as the reaction of group 1 metals but the products are the same. Ca (s) + H₂O (l) ® Ca(OH)₂ (aq) + H₂(g) The resulting solution is referred to as limewater, which when reacted with carbon dioxide produces a white precipitate (of calcium carbonate). Magnesium does not even react appreciably with water. It reacts with steam to produce magnesium oxide and hydrogen gas. Magnesium + steam ¾® Magnesium oxide + hydrogen Mg _(s) + H₂O _(g) ¾® MgO _(s) + H_{2 (g)}
34	Reaction of Group 2 Metals with Water Group 2 metals like magnesium and calcium react very slowly with cold water (fig.1), but quickly with steam (fig.2).
35	How do Group 2 metal atoms react? They react by donating their 2 valence electrons.
36	Reactivity of Group 2 and 3 Metals Since calcium reacts with water while magnesium requires steam, calcium is more reactive than magnesium. In other words, reactivity increases going down group 2 as well just as with group 1 metals for the same reason. Therefore, going Down Group 2 EASIER to LOSE OUTER ELECTRON So MORE CHEMICALLY REACTIVE That is, it is easier for Ba to lose two electrons than it is for Ca. And it is easier for Ca to lose two electrons than it is for Mg etc.
37	Reactivity of Group 2 and 3 Metals Ba is more reactive than Ca. Ca is more reactive than Mg. Reactivity increases going down the group of group 2 metals. Similarly, since sodium reacts with cold water but magnesium requires steam, sodium is more reactive than magnesium. In general then, going across the periodic table metals get less reactive. Potassium is more reactive than calcium for instance. Aluminum, another metal in the same period as sodium and magnesium is even less reactive than magnesium. (Can you tell why aluminum would be less reactive than magnesium?) So, going across a period, the reactivity of metals in the period decreases.
38	Summary Atoms of metals have less than four electrons in their valence shell. When they react with other elements metal atoms lose their valence electrons to attain a structure similar to that of a noble gas so that they are stable. The number of electrons metal atoms lose is equal to the group number the metal belongs to. Within metals, the reactivity increases as you go down the group as the valence electron(s) are held less and less strongly because they are found farther and farther away from the attractive influence of the nucleus. Density, melting point, and boiling point also decreases going down group 1 and group 2 metals.
39	Summary Within a period, going across from group 1 to group 3 metals, the reactivity decreases as it get harder and harder for metal atoms to lose the number of electrons they do need to lose to become stable.
40	Practice Questions 1. N04/2/1. The table below gives some information about the elements in Group I of the Periodic Table.
41	Practice Questions (a) How does the density of the Group I elements change down the Group? [2] (b) Suggest a value for the boiling point of rubidium. [1] (c) Suggest a value for the radius of a caesium atom. [1] (d) Use the information in the table to suggest how fast lithium reacts with water compared with the other Group I metals. [1] (e) State three properties shown by all metals. [3]
42	Practice Questions (f) When sodium reacts with water, hydrogen is given off. 2Na(s) + 2H₂O(l) à 2NaOH(aq) + H₂(g) (i) State the name of the other product formed in this reaction. [1] (ii) Describe a test for hydrogen. test result [2] (g) Explain the different reactivity of sodium and potassium with water. [2]