PeriodicityPeriodicity

GlencoeGlencoe

Chapter 6Chapter 6

DevelopmentDevelopmentof theof the

Modern Periodic TableModern Periodic Table1790s – 23 known elements1790s – 23 known elementsBy 1870s – 70 known elementsBy 1870s – 70 known elements1864 - John Newlands proposed arrangements by mass 1864 - John Newlands proposed arrangements by mass and properties by octavesand properties by octaves1864 – Lothar Meyer proposes arrangements by mass 1864 – Lothar Meyer proposes arrangements by mass and columns of properties—but doesn’t publish!and columns of properties—but doesn’t publish!1869 – Dmitri Mendeleev also proposed arrangements 1869 – Dmitri Mendeleev also proposed arrangements by mass and columns of properties—and announces!by mass and columns of properties—and announces! 1913 – Henry Moseley proposed arrangements by 1913 – Henry Moseley proposed arrangements by atomic number. (periodic law)atomic number. (periodic law)

Newlands’ “octaves”Newlands’ “octaves”H 1 F 8 Cl 15 Co/Ni 22 Br 29 Pd 36 I  42 Pt/Ir 50

Li 2 Na 9 K 16 Cu 23 Rb 30 Ag 37 Cs 44 Tl 53

Gl 3 Mg 10 Ca 17 Zn 25 Sr 31 Cd 34 Ba/V 45 Pb 54

Bo 4 Al 11 Cr 18 Y 24 Ce/La 33 U 40 Ta 46 Th 56

C 5 Si 12 Ti 19 In 26 Zr 32 Sn 39 W 47 Hg 52

N 6 P 13 Mn 20 As 27 Di/Mo 34 Sb 41 Nb 48 Bi 55

O 7 S 14 Fe 21 Se 28 Ro/Ru 35 Te 43 Au 49 Os 51

Shortly after, his ideas were presented to the Russian Physico-chemical Society. They were read by Professor Menschutkin because Mendeleev was ill. His ideas were then published in the main German chemistry periodical of the time, Zeitschrift fϋr Chemie.

                                                                                                                                                                                                    

                                            The world’s first view of Mendeleev’s Periodic Table – an extract from Zeitschrift fϋr Chemie, 1869. Click here for a translation

Key “landmarks”Key “landmarks”of theof the

modern periodic tablemodern periodic tablePeriods (horizontal)Periods (horizontal)Groups/families (vertical)Groups/families (vertical)Representative elementsRepresentative elements s & p blocks & p block Groups 1A – 8AGroups 1A – 8A Groups 1,2,13,14,15,16,17,18Groups 1,2,13,14,15,16,17,18

Transition elementsTransition elements d block (f block = “inner transition elements”)d block (f block = “inner transition elements”) Groups 1B – 8BGroups 1B – 8B Groups 3 - 12Groups 3 - 12

Other notable classifications:Other notable classifications:

MetalsMetals Alkali (group 1)Alkali (group 1) Alkaline (group 2)Alkaline (group 2)

MetalloidsMetalloids

NonmetalsNonmetals Halogens (group 17)Halogens (group 17) Noble gases (group 18)Noble gases (group 18)

Organizing Elements by Electron Organizing Elements by Electron ConfigurationConfiguration

Valence ElectronsValence Electrons Atoms in the same group have similar chemical Atoms in the same group have similar chemical

properties b/c they have the same # if valence properties b/c they have the same # if valence electronselectrons

Valence Electrons and PeriodsValence Electrons and Periods Energy level of valence electrons indicates the Energy level of valence electrons indicates the

period on the PTperiod on the PT

Valence Electrons and Group NumberValence Electrons and Group Number Group # = # valence electronsGroup # = # valence electrons Exception: HeliumException: Helium

The s-, p-, d-, and f- block elementsThe s-, p-, d-, and f- block elements s-blocks-block p-blockp-block d-blockd-block f-blockf-block

Periodic trendsPeriodic trends

Vary systemicallyVary systemically across a period (horizontally)across a period (horizontally) along a group (vertically)along a group (vertically)

Atomic radiiAtomic radii

Based on probability of electron cloud, Based on probability of electron cloud, therefore, defined by how closely an atom therefore, defined by how closely an atom lies to a neighboring atomlies to a neighboring atom

DECREASES to the right across a periodDECREASES to the right across a period Due to larger nuclear attraction Due to larger nuclear attraction

INCREASES down a groupINCREASES down a group Due to more “layers” of electronsDue to more “layers” of electrons

Ionic RadiiIonic Radii

Ions (charged atoms) form when electrons Ions (charged atoms) form when electrons are gained or lost….(the number of are gained or lost….(the number of protons and electrons don’t match!)protons and electrons don’t match!)

DECREASES to the right across a period DECREASES to the right across a period (in two phases)(in two phases)

INCREASES down a groupINCREASES down a group

Ionization EnergyIonization Energy

Defined as “amount of energy required to remove an Defined as “amount of energy required to remove an electron from a gaseous atom”electron from a gaseous atom”

11stst ionization energy ionization energy 22ndnd ionization energy ionization energy Etc.Etc.

Think of this as the atom’s ability to hold onto its valence electron!Think of this as the atom’s ability to hold onto its valence electron!

INCREASES across a periodINCREASES across a period Harder to remove e-Harder to remove e- Positive energy means “harder”Positive energy means “harder”

DECREASES down a groupDECREASES down a group Easier to remove e-Easier to remove e- More negative energy means “easier” or “more stable”More negative energy means “easier” or “more stable”

Element I1 I2 I3 I4 I5 I6 I7

Na 490 4560          

Mg 735 1445 7730        

Al 580 1815 2740 11,600      

Si 780 1575 3220 4350 16,100    

P 1060 1890 2905 4950 6270 21,200  

Octet RuleOctet Rule

Atoms tend to gain, lose, or share Atoms tend to gain, lose, or share electrons in order to acquire a full set of electrons in order to acquire a full set of eight valence electronseight valence electrons Note chemical stability of noble gasesNote chemical stability of noble gases Predicts ionic charge of main block elementsPredicts ionic charge of main block elements

CATIONS—positively charged ions CATIONS—positively charged ions (lost e-)(lost e-)

ANIONS—negatively charged ions ANIONS—negatively charged ions (gained e-)(gained e-)

Electron AffinityElectron Affinity

Energy associated with adding an electron to an Energy associated with adding an electron to an atom’s electron cloud---atom’s electron cloud---think of the opposite of think of the opposite of Ionization Energy…but same effect!Ionization Energy…but same effect!

INCREASES (but the energy gets more negative INCREASES (but the energy gets more negative = means “more stable”) across period= means “more stable”) across periodDECREASES (but the energy value gets more DECREASES (but the energy value gets more positive = means “more difficult”) down grouppositive = means “more difficult”) down group

Therefore, a great idea!....Therefore, a great idea!....

ElectronegativityElectronegativity

IndicationIndication of the relative ability of the atom of the relative ability of the atom to attract electrons in a chemical bondto attract electrons in a chemical bond Think of this quantity as how strongly an atom Think of this quantity as how strongly an atom

might want to gain an electron.might want to gain an electron.

Arbitrary rating scaled to 4.0…..Arbitrary rating scaled to 4.0….. Most electronegative element is fluorine with Most electronegative element is fluorine with

3.983.98

INCREASES across a periodINCREASES across a periodDECREASES down a groupDECREASES down a group

Summary of TrendsSummary of Trends