Ch # 6Ch # 6

Electronic Structure and Electronic Structure and Chemical Periodicity.Chemical Periodicity.

The Periodic LawThe Periodic Law: :

It states that when elements are arranged in It states that when elements are arranged in increasing atomic number, the elements increasing atomic number, the elements with similar chemical behaviors occur with similar chemical behaviors occur periodically.periodically.

The Periodic tableThe Periodic table: :

It is a tabular arrangement of elements in It is a tabular arrangement of elements in order of increasing atomic number. order of increasing atomic number. Elements having the same chemical Elements having the same chemical behaviors are grouped together in a vertical behaviors are grouped together in a vertical column called a group.column called a group.

The Periodic tableThe Periodic table: :

Each element is represented in a square Each element is represented in a square box, which contains:box, which contains:

Symbol, atomic number, atomic mass Symbol, atomic number, atomic mass number of an element.number of an element.

Periods and Groups of Elements:Periods and Groups of Elements:

Period: A horizontal row of elements. Period: A horizontal row of elements. There are 7 periods.There are 7 periods. The first period contains only two elements The first period contains only two elements

H and He.H and He. Groups: A vertical column in the periodic Groups: A vertical column in the periodic

table.table. All elements in same groups have similar All elements in same groups have similar

chemical properties.chemical properties.

Periods and Groups of Elements:Periods and Groups of Elements: There are 18 groups.There are 18 groups. Group 1A= alkali metals. Except H. React Group 1A= alkali metals. Except H. React

violently with water.violently with water. Group II A= alkaline Earth metals. Do not Group II A= alkaline Earth metals. Do not

react in water.react in water. Group VII A=Halogens. Very reactive Group VII A=Halogens. Very reactive

colored gases.colored gases. Group VIII A= Noble or inert gases. Very Group VIII A= Noble or inert gases. Very

unreactiveunreactive

Periods and Groups of Elements:Periods and Groups of Elements:

B groups= Transition elements.B groups= Transition elements. Extension of period 6=Lanthanides.Extension of period 6=Lanthanides. Extension of period 7= Actinides.Extension of period 7= Actinides. The metals lie to the left of the table. The metals lie to the left of the table.

Nonmetals to the right. They are separated Nonmetals to the right. They are separated by a step up ladder.by a step up ladder.

In between this ladder are the metalloids.In between this ladder are the metalloids.

The Shape of the Periodic TableThe Shape of the Periodic Table: :

Lanthanides, Actinides. Lanthanides, Actinides.

The Energy of an electronThe Energy of an electron: :

1. subatomic particle.1. subatomic particle. 2. They have very little mass compared to 2. They have very little mass compared to

proton and Neutrons.proton and Neutrons. 3. Located outside the nucleus.3. Located outside the nucleus. 4. Move around the nucleus in a volume that 4. Move around the nucleus in a volume that

defines the Size of the atom.defines the Size of the atom.

The Energy of an electronThe Energy of an electron::

In 1926 Schrodinger showed that laws of In 1926 Schrodinger showed that laws of quantum mechanics could be used to quantum mechanics could be used to characterize the motion of electrons.characterize the motion of electrons.

A quantized property is a property that can A quantized property is a property that can have only certain values.have only certain values.

The energy of an electron is quantized, only The energy of an electron is quantized, only certain behavior patterns are allowed.certain behavior patterns are allowed.

Electron Shells Electron Shells

Electrons with higher energy have higher Electrons with higher energy have higher velocity and thus they move farther away velocity and thus they move farther away from the nucleus.from the nucleus.

Electron shellElectron shell A region in space about a nucleus that A region in space about a nucleus that

contains electrons that have approximately contains electrons that have approximately the same energy and that spend most of the same energy and that spend most of their time approximately the same distance their time approximately the same distance from the nucleus.from the nucleus.

Electron shellElectron shell ““n” is used to identify each electron shell.n” is used to identify each electron shell. Electron energy increases as its distance Electron energy increases as its distance

from nucleus increases.from nucleus increases. Shell energy capacity = 2n2, where n is Shell energy capacity = 2n2, where n is

shell number.shell number. 7 shells maximum.7 shells maximum. Shell # 1 has 2e, 2 has 8 es, 3 has 18 es, 4 Shell # 1 has 2e, 2 has 8 es, 3 has 18 es, 4

has 32 es.has 32 es.

Electron SubshellsElectron Subshells: :

A region of space within an electron shell that A region of space within an electron shell that contains electrons that have the same energy.contains electrons that have the same energy.

Number of subshells in a shell=n, n= shell number.Number of subshells in a shell=n, n= shell number. The letters s, p, d, f in order indicate energies of The letters s, p, d, f in order indicate energies of

the subshells.the subshells. S=2 es, p=6 es, d=10 es, f=14 es.S=2 es, p=6 es, d=10 es, f=14 es. Total number of electrons in shell 1=_______, Total number of electrons in shell 1=_______,

shell 2=____ shell 3=___ shell 4=___-.shell 2=____ shell 3=___ shell 4=___-.

Electron orbitalsElectron orbitals: :

A region of space within an electron A region of space within an electron subshell where an electron with a specific subshell where an electron with a specific energy is most likely to be found.energy is most likely to be found.

S subshell=1 orbital, p subshell=3 orbitals, d S subshell=1 orbital, p subshell=3 orbitals, d subshell=5 orbitals, f subshell=7 orbitals.subshell=5 orbitals, f subshell=7 orbitals.

Maximum number of electrons in a subshell Maximum number of electrons in a subshell is always 2.is always 2.

S orbital=spherical, p orbital =dumbbell S orbital=spherical, p orbital =dumbbell shaped.shaped.

Electron SpinElectron Spin

: Property of an electron associated with its : Property of an electron associated with its spinning on its own axis.spinning on its own axis.

Pauli's exclusion Principle: The maximum Pauli's exclusion Principle: The maximum number of electrons in any orbital is two and number of electrons in any orbital is two and they are spinning in the opposite directions.they are spinning in the opposite directions.

Electron ConfigurationsElectron Configurations

A statement of how many electrons an atom A statement of how many electrons an atom has in each of its subshells.has in each of its subshells.

Aufbau PrincipleAufbau Principle

: It states that electrons normally occupy : It states that electrons normally occupy electron subshells in an atom in order of electron subshells in an atom in order of increasing subshell energy.increasing subshell energy.

Subshells are filled in order of increasing Subshells are filled in order of increasing energy.energy.

Aufbau DiagramAufbau Diagram: :

Listing of electron subshells in the order in Listing of electron subshells in the order in which electrons occupy them.which electrons occupy them.

Orbital DiagramsOrbital Diagrams

Two principles to be considered are The Two principles to be considered are The Aufbau’s principle and Hund’s rule.Aufbau’s principle and Hund’s rule.

A diagram that shows how many electrons A diagram that shows how many electrons an atom has in each of its occupied electron an atom has in each of its occupied electron orbitals.orbitals.

Hund’s RuleHund’s Rule

It states that when electrons are placed in a It states that when electrons are placed in a set of orbitals of equal energy the order of set of orbitals of equal energy the order of filling the orbitals is such that each orbital filling the orbitals is such that each orbital will be occupied by one electron before any will be occupied by one electron before any orbital receives a second electron. This orbital receives a second electron. This minimizes the repulsion between the minimizes the repulsion between the electrons.electrons.

Orbital DiagramsOrbital Diagrams

Paired electronsPaired electrons: Two electrons of opposite : Two electrons of opposite spin present in the same orbital.spin present in the same orbital.

Unpaired electronUnpaired electron: A single electron in an : A single electron in an orbital.orbital.

Orbital diagramOrbital diagram

Paramagnetic atomParamagnetic atom: An atom that has an : An atom that has an electron arrangement containing one or electron arrangement containing one or more unpaired electrons.more unpaired electrons.

Diamagnetic atomDiamagnetic atom: It is an atom that has an : It is an atom that has an electron arrangement in which all electrons electron arrangement in which all electrons are paired.are paired.

Electronic configurations and The Electronic configurations and The periodic Lawperiodic Law

Chemical properties repeat themselves in a Chemical properties repeat themselves in a repeated manner because electronic repeated manner because electronic configurations repeat themselves.configurations repeat themselves.

Group number indicates the number of valence Group number indicates the number of valence electrons in atom.electrons in atom.

Valence electrons are the electrons that can loose, Valence electrons are the electrons that can loose, gain or be shared in chemical reactions.gain or be shared in chemical reactions.

Group 1=1 valence electron, group 7= 7 valence Group 1=1 valence electron, group 7= 7 valence electrons.electrons.

Electronic Configurations and The Electronic Configurations and The Periodic TablePeriodic Table

S area has 2 columns.S area has 2 columns. P area has 6 columns.P area has 6 columns. D area has 10 columns.D area has 10 columns. F area has 14 columns.F area has 14 columns.

Electronic Configurations and The Electronic Configurations and The Periodic TablePeriodic Table

Distinguishing Electron: Last electron added Distinguishing Electron: Last electron added to the element’s electronic configuration to the element’s electronic configuration when the configuration is written according when the configuration is written according to Aufbau principle.to Aufbau principle.

All elements in the first column of a specific All elements in the first column of a specific area contain 1 electron, second column area contain 1 electron, second column contains 2 electrons ------.contains 2 electrons ------.

Electronic Configurations and The Electronic Configurations and The Periodic TablePeriodic Table

Shell number=period number.Shell number=period number. For d area shell number=period number-1.For d area shell number=period number-1. For f area shell number=period number-2. For f area shell number=period number-2.

Classification Systems for the Classification Systems for the Elements:Elements:

A noble gas element: group VIII A. All A noble gas element: group VIII A. All elements are gases. Do not react.All have 8 elements are gases. Do not react.All have 8 electrons around them , other than He.electrons around them , other than He.

A representative element: Located in s area A representative element: Located in s area or first 5 columns of the p area.or first 5 columns of the p area.

Transition element: Element located in d Transition element: Element located in d areaarea

Inner transition element: Located in the f Inner transition element: Located in the f area of periodic table.area of periodic table.

Based on physical properties:Based on physical properties:

Metals: luster, thermal conductivity, Metals: luster, thermal conductivity, electrical conductivity, malleable, ductile.electrical conductivity, malleable, ductile.

All metals are solid , except Hg.All metals are solid , except Hg. High density and high melting points.High density and high melting points. Ex: Al, Fe. Cu, Zn, Ag, Au.(91 elements)Ex: Al, Fe. Cu, Zn, Ag, Au.(91 elements) Left of periodic table, zigzag lineLeft of periodic table, zigzag line

Based on physical properties:Based on physical properties:

Nonmetals: no luster, not malleable, not Nonmetals: no luster, not malleable, not ductile, not good conductors.ductile, not good conductors.

Gases at RT, except: Br-liquid.Gases at RT, except: Br-liquid. Lower densities, low Melting points.Lower densities, low Melting points. Ex: C,S, P.(22 elements)Ex: C,S, P.(22 elements) Right of periodic table, zigzag line.Right of periodic table, zigzag line. Earth’s crust contains: O,Si,H.Earth’s crust contains: O,Si,H.

Chemical PeriodicityChemical Periodicity: :

The variation in properties of elements as a The variation in properties of elements as a function of their positions in the Periodic function of their positions in the Periodic Table.Table.

Metallic and Nonmetallic CharacterMetallic and Nonmetallic Character: :

Metallic character increases right to left, in Metallic character increases right to left, in a period.a period.

It increases from top to bottom in a group.It increases from top to bottom in a group. Nonmetallic character increases from left Nonmetallic character increases from left

to right in a period.to right in a period. Nonmetallic character increases from Nonmetallic character increases from

bottom to top in a group. bottom to top in a group.

MetalloidMetalloid: :

Element that possess properties both of Element that possess properties both of metals and nonmetals. Ex: Si, Ge Sb metals and nonmetals. Ex: Si, Ge Sb

SemiconductorSemiconductor: :

An element that does not conduct electric An element that does not conduct electric current at room temperature but does so at current at room temperature but does so at higher temperature.higher temperature.

Atomic SizeAtomic Size: :

Unit for atomic radii is picometer. Unit for atomic radii is picometer. Range is 50-200 pm.Range is 50-200 pm. Atomic radii decreases from left to right Atomic radii decreases from left to right

within a period.within a period. Atomic radii increases from top to bottom Atomic radii increases from top to bottom

within a group. within a group.