Instructor: Dr. Robert Powers Office Address: 722 HaH Phone: 472-3039 e-mail:[email protected] web...

Instructor: Dr. Robert Powers OfficeAddress: 722 HaHPhone: 472-3039e-mail:[email protected]

web page: http://bionmr-c1.unl.eduhttp://bionmr-c1.unl.edu

September 11, 2001

NEVER FORGET

Periodic Table Chemical Trends

Periodicity in chemical properties is the basis of the periodic table arrangement

Periodicity of electron configuration:

- Affects attraction of atom for its valence electrons

- Affects attraction of valence electrons for additional electrons

Determines chemical Determines chemical and physical properties and physical properties of the elementsof the elements

Periodic Table

Copper (solid)

Mercury (liquid)

Chemical Trends

Hydrogen (gas)

1s1

[Ar]3d104s1

[Xe]5d106s2


1.) Chemical trends based on the combination of the electron configuration, octet rule and electronegativity

2.) Electronegativitya.) tendency to attract electrons in a compoundb.) empirically based range from 0.7 to 3.98

Attracts electrons

Donate electrons



2.) ElectronegativityHigh electronegativity pulls electrons away from elements with weaker electronegativity

Low electronegativity easily loses electrons to elements with higher electronegativity



3.) The Octet Rule

The representative elements achieve a noble-gas configuration (eight valence electrons) in most of their compounds, except hydrogen, which only has two valence electrons in its corresponding noble gas structure.


4.) Chemical reactions between Group IA elements and Group VIIA elements Group IA – single valence electron easily removed noble configuration Group VIIA – easily attracts one electron noble configuration (ns2p6) Form 1:1 ionic compound where Group IA loses e- and Group VIIA gains e-

Ionic compounds are usually solids

ns1 ns2p5

low

high

Chemical Trends

5.) Electronegativity differences determine the outcome of a chemical reaction Electronegativity of Chlorine is 3.16 Electronegativity of Bromine is 2.96

Halogen ions have an octet in valence shell

No need to share e-

Periodic Table

clear pale yellow dark brown clear

2Br- has sixteen valence electrons (eight each)

Br2 has only fourteen valence electrons

Two electrons lost from two Br-

Two electrons gained by Cl2 to form 2Cl-

The greater electronegativity of chlorine captures an electron from bromide


6.) Example: electronegativity difference determines chemical productsHalides are expected to react similarly with water, but there are some important differences. Why?

Answer:electronegativities: chlorine 3.16, oxygen 3.4, fluorine 3.98

fluorine can attract e- from oxygen- HF : eight valence electrons- O2 : six valence electrons

chlorine can not attract e- from oxygen, instead attracts e- from hydrogen in water and replaces hydrogen in water

- HCl : eight valence electrons- HOCl : Cl replaces H in water

Clicker Question

Clicker Question:What is a main factor that results in an atom having an increasing What is a main factor that results in an atom having an increasing

atomic radius compared to its neighbor?atomic radius compared to its neighbor?

a) total number of electrons

b) total number of protons and neutrons

c) total number of electrons in the outer electron shell

d) total number of electron shells


7.) Size of AtomAtomic radius – radius of the sphere containing 90% of the electron density for the

free atom related to electronic configurationProgressing from period to period

the valence shell is increasing far from the nucleus increased separation of negatively charged electrons from positive

charged protons Size of the atoms and ions increase

Incr

easi

ng

Ato

mic

Rad

ius


7.) Size of AtomProgressing from group to group

the valence shell is a constant increased attraction between the negatively charged electrons from

positive charged protons all e- are drawn to the nucleus Size of the atoms and ions decrease despite adding electrons Minimal size change occurs for transition elements

- fill inner shell d-orbitals that shield outer shell s-orbitalsDecreasing Atomic Radius


7.) Size of AtomChanges in Size Affects Chemical Behavior

Decrease in RadiusIncrease in attractionbetween nucleus and

electrons

Increase in:ionization energy electron affinityelectronegativity


8.) Size of IonWhen an atom gains or loses an electron, the ion is a different size than the neutral atom

Like Charges Repel:

Remove e- remove repulsion smallerpositive charged ion (cation) is smaller

Add e- add repulsion largernegatively charged ion (anion) is larger

Size difference can be dramatic, about a factor of 2


8.) Size of IonWhen an atom gains or loses an electron, the ion is a different size than the neutral atom

Like Charges Repel:

Isoelectronic ions are bigger the greater the negative chargeAgain, greater nuclear charge can hold electrons closer than smaller nuclear charge

2s22p6: 7N3- > 8O2- > 9F- > 11Na+ > 12Mg2+ > 13Al3+

171 140 133 102 72 50 picometers (pm)


9.) Example: converting mass density to molar and atomic densityGiven a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume.

33

cm/molmol/g

cm/g

massatomic

densitymassvolume/molesdensityMolar

33

116086747

545

86747

cm/mol.mol/g.

cm/g.densitymolar

mol/g.massatomic

:Ti

33

116084555

8747

84555

cm/mol.mol/g.

cm/g.densitymolar

mol/g.massatomic

:Fe

Solution:Calculate Molar

Density:



Solution:Calculate

Atomic Density:3

3cm/atoms

mol

atomsx

mol/g

cm/gmole/atoms

massatomic

densitymassvolume/atomsdensityAtomic

322233 109961002213761160 cm/atoms.mol/atomsx.cm/mol. :Ti

322233 10491810022137614100 cm/atoms.mol/atomsx.cm/mol. :Fe



Solution:Calculate Volume per Atom in

the Solid: densityatomic/solidinatomperVolume 1

atom/cm.cm/atoms. 323322 10431109961 /:Ti

atom/cm.cm/atoms. 323322 1017811049181 /:Fe

Calculate Atomic Volume:

atombyoccupiedfractionatompervolumevolumeAtomic

atom/cmx..atom/cm. 323323 1006174010431 :Ti

atom/cmx..atom/cm. 324323 10018680101781 :Fe



Solution:Calculate Atomic Radius:

34

3

volumeatomic

radiusAtomic

3

3

4rspherevolume

pmcm.cm.

: 136103614

100613 83323

Ti

pmcm.cm.

:e 124102414

100183 83324

F

200 pm

172 pm

Smaller than atomic radius because of interatomic interactions

Periodic Table Trends in Physical Properties

1.) Classification of the Elements Elements in Periodic table are classified into three broad

categories

Metals

Nonmetals

Semimetals

Metallic character associated with few valence s and p electrons and increases as those electrons are located farther from the nucleus

Increasing metal characteristics


1.) Classification of the Elements Metals

Vast majority (~75%) of the elements Left-hand of the periodic table Defined by being:

Malleable – pounded into a sheet Ductile – drawn into a wire Most are solid at room temperature Silvery shiny sheen Conduct heat and electricity well Low electronegativity values Low ionization energy

Valence electrons held looselyFacile movement of metal atoms over each other in solid


1.) Classification of the Elements Nonmetals

Right-side of the periodic table Defined by being:

Variable physical states Solids are brittle and poor conductors of heat and electricity Insulating solids high electronegativity values

Allotropes: different forms of the same elements with different properties Carbon:

- diamond: hardest material known cutting tool

- graphite: conductor, lubricant but not malleable or ductile

- “bucky balls”

Bucky ball Graphite Diamond


1.) Classification of the Elements Semimetals (metalloids)

Smallest number of elements Fall between metals and nonmetals Some properties common to metals others to nonmetals Defined by being:

Solids at room temperature Brittle Poor conductors of electricity

Semiconductors: increasing conductivity with temperature properties Metals conductivity decrease with temperature Silicon (Si) and Germanium (Ge)

Silicon wafer


2.) Physical Form of the Elements Phase of the elements at room temperature also reveals a periodic variation.

Most elements are solids, some are gases, few are liquids Except for 1st period every period begins with solid and ends with gas

Different interactions among atoms of the element

solid gas


3.) Interactions and the Three Phases of Matter Solids – holds its shape without support of a container

Interactions in solid must be strong Liquids – adopt shape of container

Atoms in liquid flow readily over one another Interactions are weaker than in a solid

Gas – expands to fill container Interactions are very weak


4.) Phase Transitions: transforming from a solid to a liquid and from a liquid to a gas

Solid Liquid Gas

Decreasing temperature Increasing temperature

Melting point

Freezing point

Boiling point

Condensation point

Increasing energyDecreasing energy

Instructor: Dr. Robert Powers Office Address: 722 HaH Phone: 472-3039 e-mail:[email protected] web...

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Transcript of Instructor: Dr. Robert Powers Office Address: 722 HaH Phone: 472-3039 e-mail:[email protected] web...