Periodic Trends Section 7.7-7.8
A Different Type of Grouping
• Broader way of classifying elements:• Metals
• Nonmetals
• Metalloids or Semi-metals.
Metals, Nonmetals, Metalloids
• There is a zig-zag or staircase line that divides the table.
• Metals are on the left of the line, in blue.
• Nonmetals are on the right of the line, in orange.
Metals, Nonmetals, Metalloids
• Elements that border the stair case, shown in purple are the metalloids or semi-metals.
• Aluminum is more metallic than not.
Metallic Character
• Degree to which an element exhibits the physical and chemical properties of a metal.
Metals
• Metals are lustrous (shiny), malleable, ductile, and are good conductors of heat and electricity.
• They are mostly solids at room temp.
• What is one exception?
Nonmetals
• They are dull, brittle, nonconductors (insulators).
• Some are solid, but most are gases
• One is liquid…which is it?
Ionic Compounds
• Form between metal and nonmetal
• Metal oxides are bases• React with acids to form salt and water
Metals lose e-s Nonmetals gain e-
s
A common feature of transition metals is that they often form cations of several different charges. Cr, for example, can be found as Cr2+ , Cr3+ or Cr6+ . Ag and Zn are exceptions to this observation. Ag forms Ag+ ions only, Zn forms Zn2+ ions only
Molecular Compound
• Nonmetals combine with each other to form molecular compounds.
• Nonmetallic oxides, like CO2 or SO2 are acidic in aqueous solution.
Metalloids
• Characteristics of both metals and nonmetals.
• They are shiny but brittle
• Semiconductors
Overall Reactivity
• The most reactive metals are the largest since they are the best electron givers.
• The most reactive nonmetals are the smallest ones, the best electron takers.
Group Trends: Alkali Metals• Alkali Metals: ns1
• Soft metallic solids
• Na and K most abundant in Earth’s crust and biological systems
• Physical properties on Table 7.4 on pg. 281
Group Trends: Alkali Metals
• Very reactive
• Exist in nature only as compounds
• React with hydrogen to form hydrides• H- is a hydride ion
• And with sulfur to form sulfides
Group Trends: Active Metals
• React vigorously with H2O• 2Na(s) + 2H2O(l) ---> H2(g) +2NaOH(aq)
• Very exothermic
• Reacts with oxygen • 4Li + O2 (g) 2Li2O (s)
• Metal oxide (only Li with O2-)
• 2Na + O2 (g) 2Na2O2 (s)• Metal peroxides (all other alkali with O2
2- )
• K(s) + O2 (g) KO2 (s)• K, Rb, Cs form superoxides with O2
- ion
The Alkaline Earth Metals
• Solid at room temperature
• ns2
• Table 7.5 on page 285
• Harder and more dense than alkali
• Less reactive than alkali• Be and Mg are the least reactive
The Alkaline Earth Metals
• Be does not react with water or steam
• Mg does not react with water, but will with steam• Mg(s) + H2O (g) MgO(s) + H2 (g)
• All others react with water• Ca(s) + 2H2O (l) Ca(OH)2 (aq) + H2(g)
The Alkaline Earth Metals
• Heavier alkaline earth ions give off characteristic colors when strongly heated in a flame• Ca = brick red
• Sr = crimson red
• Ba = green
• Mg and Ca are essential to the growth and maintenance of the human body• 99% of Ca in body is in skeletal system
The Alkaline Earth Metals
Hydrogen 1s1
• is a nonmetallic element in a class by itself- but is metallic inside the stars & Jovian planets
• the most abundant element in the universe.
• forms explosive mixtures with oxygen and halogens.
• Can react with metals to form hydrides.
• Can lose it’s e- in H2O to
• form H+ ions.
Group 16 ns2,np4
• Oxygen group• O, S, and Se are
nonmetallic• Te is a metalloid• Po is a radioactive, rare
metal• Two allotropes of Oxygen• Oxygen is a great oxidizer• Sulfur has many allotropes
• S8 is the most common
• Sulfur reacts with almost every metal to form sulfides.
Group 17 ns2,np5
• Nonmetallic• Halogens = salt formers• As is rare and radioactive• They are all very reactive
and not found in their free form.
• Cl has the most industrial use
• Reactivity: F2 > Cl2 > Br2 > I2
• The smaller the atomic size the more reactive the nonmetallic atom
Group 18 ns2,np6
• Noble Gases. • Each of these elements has a full
component of “p” electrons (except He).
• They are all unreactive• Used to be called the inert gases
• He is commercially available, but is very expensive.
• Ar is more common as less than 1% of the air