Development of thePeriodic Table

John Newlands - Law of Octaves

1864

When arranged in order of atomic mass, every eighth element had similar properties.

Dimitri Mendeleev / Lothar Meyer

1869

organized elements arranged according to atomic mass.

Mendeleev showed how useful the table could be in predicting the existence and properties of yet unknown elements

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Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.

Modern Periodic Table - Henry Mosley

20th Century

Organized according to atomic number.

an elements position on the periodic table gives indications

of its various physical and chemical properties

Metals, Nonmetals and Metalloids

Metals Nonmetals

In chemical reactions metals tend to lose electrons to nonmetals

Metalloids

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Properties of Metal, Nonmetals,and Metalloids

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Metals versus Nonmetals• Metals tend to form cations.• Nonmetals tend to form anions.

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Metals

Metals tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.

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Metals• Compounds formed between metals and

nonmetals tend to be ionic.• Metal oxides tend to be basic.

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Nonmetals

• Nonmetals are dull, brittle substances that are poor conductors of heat and electricity.

• They tend to gain electrons in reactions with metals to acquire a noble-gas configuration.

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Nonmetals

• Substances containing only nonmetals are molecular compounds.

• Most nonmetal oxides are acidic.

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Metalloids

• Metalloids have some characteristics of metals and some of nonmetals.

• For instance, silicon looks shiny, but is brittle and a fairly poor conductor.

metalsgood conductors of heat and electricity

malleable

ductile

lustrous

tend to lose electrons in chemical reactions

nonmetalspoor conductors

brittle

tend to gain electrons in chemical reactions

Specific Groups

Main groupsgroup numbers identified by suffix A

Main group metalsAlkali metals Alkaline earth metals

NonmetalsHalogens Noble gases

transition metalsLanthanidesActinides

Periodic Classification ofthe Elements

Valence Electrons

The outer electrons of an atom, which arethose involved in chemical bonding, are often called the valence electrons.

Elements in the same group of the periodictable have analogous valence-electron figurations.

Group 8A

1

2

3

4

6

5

He

Ne

Ar

Kr

Rn

Xe

1s2

[He]2s22p6

[Ne]3s23p6

[Ar]3d104s24p6

[Xe]5d104f146s26p6

[Kr]4d105s25p6

noble gases

Group 1A

1234

65

7

HLiNaK

CsRb

Fr

1s1

[He]2s1

[Ne]3s1

[Ar]4s1

[Xe]6s1

[Kr]5s1

[Rn]7s1

alkali metals

Group 2A

234

65

7

BeMgCa

BaSr

Ra

[He]2s2

[Ne]3s2

[Ar]4s2

[Xe]6s2

[Kr]5s2

[Rn]7s2

Alkaline earth metals

Group 7A

234

65

FClBr

AtI

2s2 2p5

3s2 3p5

4s2 4p5

6s2 6p5

5s2 5p5

halogens

Ions

When electrons are removed from or added to a neutral atom or molecule, a

charged particle called an ion is formed.

Ions

Positively charged ions are calledcations

Negatively charged ions are calledanions

Ions

positively charged: cations

negatively charged: anions

most common type is metal cationNa+, Ca2+, Al3+, Fe2+, Fe3+

most common type is nonmetal anionCl–, O2–

the chemical behavior of an atom

depends on how hard an atom holds on to its electrons

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Effective Nuclear Charge

• In a many-electron atom, electrons are both attracted to the nucleus and repelled by other electrons.

• The nuclear charge that an electron experiences depends on both factors.

Metals Nonmetals

In chemical reactions metals tend to lose electrons to nonmetals

Na: 11 protons; 11 electrons

Atoms vs Ions

Cl: 17 protons; 17 electrons

Electron Configurations of Cations and Anions

Element AtomSodium Na [Ne]3s1

Magnesium Mg [Ne]3s2

Aluminum Al [Ne]3s23p1

IonNa+ [Ne]Mg2+ [Ne]Al3+ [Ne]

Isoelectronic species have the same number of electrons.

Electron Configurations of Cations and AnionsElement AtomHydrogen H 1s1 H–

Fluorine F 1s2 2s2 2p5 F–

Oxygen O 1s2 2s2 2p4 O2–

Ion 1s2

1s22s22p6

1s22s22p6

1s22s22p6Nitrogen N 1s2 2s2 2p3 N3–

Isoelectronic species have the same number of electrons.

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Alkali Metals

• Alkali metals are soft, metallic solids.

• The name comes from the Arabic word for ashes.

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Alkali Metals• They are found only in compounds in nature,

not in their elemental forms.• They have low densities and melting points.• They also have low ionization energies.

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Alkali Metals

Their reactions with water are famously exothermic.

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Alkali Metals• Alkali metals (except Li) react with oxygen to form

peroxides.• K, Rb, and Cs also form superoxides:

K + O2 ⎯⎯→ KO2

• They produce bright colors when placed in a flame.

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Alkaline Earth Metals

• Alkaline earth metals have higher densities and melting points than alkali metals.

• Their ionization energies are low, but not as low as those of alkali metals.

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Alkaline Earth Metals

• Beryllium does not react with water, and magnesium reacts only with steam, but the other alkaline earth metals react readily with water.

• Reactivity tends to increase as you go down the group.

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Group 6A

• Oxygen, sulfur, and selenium are nonmetals.• Tellurium is a metalloid.• The radioactive polonium is a metal.

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Sulfur

• Sulfur is a weaker oxidizer than oxygen.

• The most stable allotrope is S8, a ringed molecule.

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Group VIIA: Halogens

• The halogens are prototypical nonmetals.• The name comes from the Greek words halos

and gennao: “salt formers.”

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Group VIIA: Halogens

• They have large, negative electron affinities.– Therefore, they tend to oxidize

other elements easily.• They react directly with

metals to form metal halides.• Chlorine is added to water

supplies to serve as a disinfectant.

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Group VIIIA: Noble Gases

• The noble gases have astronomical ionization energies.

• Their electron affinities are positive.– Therefore, they are relatively unreactive.

• They are found as monatomic gases.