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

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?

Metals

• LOW Ionization energy form positive ions easily

• cations

Nonmetals

• They are dull, brittle, nonconductors (insulators).

• Some are solid, but most are gases

• One is liquid…which is it?

Nonmetals

• HIGH electron affinities gain electrons and become negative ions

• anions

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.

Overall Reactivity

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

Homework

• 7.54 through 7.60 on page 294• Black problems only

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

• Tendency to lose two outer 2s electrons

• Form 2+ cation

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

Group Trends

Selected Nonmetals

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

Homework

• 7.66-7.78 on page 295

• Black problems only