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The Periodic The Periodic TableTable
History of the Periodic History of the Periodic TableTable
In 1869, Dmitri Mendeleev In 1869, Dmitri Mendeleev arranged the elements according to arranged the elements according to atomic mass in an attempt to atomic mass in an attempt to classify them.classify them.
He left spaces for elements that he He left spaces for elements that he predictedpredicted existed, existed, yet hadn’t been yet hadn’t been discovered yet. discovered yet. This set him apart This set him apart from others, and he was later from others, and he was later proven correct.proven correct.
Henry Moseley
In 1913, Henry Moseley developed the concept of atomic numbers. He determined the frequencies of X-rays emitted as different elements were bombarded with high energy electrons.
Each element produces X-rays of unique frequency, and the frequency increased as atomic mass increased.
Atomic Number
Moseley arranged these frequencies in order by assigning a unique whole number, which he called the atomic number.
He correctly identified the atomic number as the number of protons in the nucleus of the atom.
This clarified some problems that Mendeleev had; Ar and K, Te and I.
Mendeleev and the Mendeleev and the Periodic LawPeriodic Law
When elements are arranged When elements are arranged in order of increasing in order of increasing atomic atomic numbernumber, their physical and , their physical and chemical properties show a chemical properties show a pattern or pattern or trend.trend.
Effective Nuclear Charge
Electrons are (-) charged and nuclei have a (+) charge.
Many properties of the atoms depend on their electron configurations and how strongly the valence electrons are attracted to the nucleus.
Effective Nuclear Charge, continued
A valence electron in an atom is attracted to the nucleus, and is repelled by the other electrons in the atom.
The inner electrons (core) are effective in shielding or blocking the nuclear attraction. (Electron shielding effect.)
Effective Nuclear Charge = +1.
Effective Nuclear Charge, continued
Zeff = Z - S Z is the number of protons in the
nucleus S is the screening constant The value of S is usually close to the
number of core electrons in the atom. The effective nuclear charge increases
as we move across a period.
Periodic Table Periodic Table ArrangementArrangement
Periods:Periods: Horizontal Rows Horizontal Rows Indicates the energy level where Indicates the energy level where
the valence electrons are the valence electrons are located. located.
ExampleExample: An element in Period : An element in Period 4 has its valence electrons in the 4 has its valence electrons in the 44thth energy level. energy level.
Periodic Table Periodic Table ArrangementArrangement
Groups/Families:Groups/Families: Vertical Vertical columnscolumns
Elements in the same column Elements in the same column have similar valence electron have similar valence electron configurations and therefore configurations and therefore similar properties.similar properties.
Example:Example: All elements in Group I All elements in Group I have 1 valence electron.have 1 valence electron.
Hydrogen is NOT a part of Group 1. It is a non-
metal and a gas.
Groups 1 and 2Groups 1 and 2
Group 1 – Alkali MetalsGroup 1 – Alkali Metals 1 valence electron1 valence electron VERY reactiveVERY reactive
Group 2 – Alkali Earth MetalsGroup 2 – Alkali Earth Metals 2 valence electrons2 valence electrons Reactive, but not as much as Group Reactive, but not as much as Group
11
Both Group 1 and Group Both Group 1 and Group 22
Reactivity increases as you go down a Reactivity increases as you go down a groupgroup
Form cationsForm cations Found as Found as compoundscompounds onlyonly , in nature , in nature Low ionization energy and low Low ionization energy and low
electronegativityelectronegativity Large radiiLarge radii Radii of positive ions are smaller than the Radii of positive ions are smaller than the
radii of atoms.radii of atoms.
Na 2e-8e-
1e-
2e-
8e-
Sodium atom with 11 electrons
Sodium ion with 10 electrons
Radius of Sodium atom versus its ion
Na
Groups 3 – 11 Groups 3 – 11 Transition ElementsTransition Elements
Metallic characteristicsMetallic characteristics Have multiple (+) ionsHave multiple (+) ions CCoolloorreedd compounds compounds
Group 17 – HalogensGroup 17 – Halogens
7 valence electrons7 valence electrons These are the most active of the non-These are the most active of the non-
metals!metals! Gains electrons easily and forms (-) ionsGains electrons easily and forms (-) ions FF22 is the most reactive and I is the most reactive and I22 is the least is the least
reactivereactive FF22 is the most electronegative and has the is the most electronegative and has the
most ionization energymost ionization energy
Group 18 – Noble GasesGroup 18 – Noble Gases
8 valence electrons8 valence electrons Inactive gases not found in Inactive gases not found in
compounds in naturecompounds in nature
Inner Transition Inner Transition ElementsElements
(Bottom Row)(Bottom Row) LanthanidesLanthanides – Lanthanoid series – ones – Lanthanoid series – ones
that follow the element Lanthanum (#57)that follow the element Lanthanum (#57) Rare earth elements that are less than Rare earth elements that are less than
0.01% in nature0.01% in nature ActinidesActinides – Actinoid series – ones that – Actinoid series – ones that
follow Actinum (#89)follow Actinum (#89) All are radioactive and unstableAll are radioactive and unstable Those after U are not found in natureThose after U are not found in nature Elements above 92 are synthetic Elements above 92 are synthetic
Broad Categories Broad Categories of the Periodic of the Periodic
TableTable
MetalsMetals The elements on the left side of the The elements on the left side of the
table.table. MalleableMalleable DuctileDuctile LustrousLustrous Conducts heat and electricityConducts heat and electricity Low ionization energies and low Low ionization energies and low
electronegativitieselectronegativities Form cations because they lose electronsForm cations because they lose electrons Mostly solidsMostly solids Reactivity increases as you go down a group.Reactivity increases as you go down a group.
Non-MetalsNon-Metals
The elements on the right side of the The elements on the right side of the tabletable Brittle as solids, with no lusterBrittle as solids, with no luster Poor conductors of heat and electricityPoor conductors of heat and electricity High ionization energies and high High ionization energies and high
electronegativitieselectronegativities Reactivities decrease as you go down a Reactivities decrease as you go down a
groupgroup Form anions because they gain electronsForm anions because they gain electrons They can be gases, liquids or solidsThey can be gases, liquids or solids
Semi-Metals (Metalloids)Semi-Metals (Metalloids)
Some properties are metallic, some Some properties are metallic, some are non-metallic and some are in-are non-metallic and some are in-betweenbetween
They are found adjacent to the They are found adjacent to the darkened line darkened line
Other information, Other information, continuedcontinued
Mono-atomic elements – He and all the Mono-atomic elements – He and all the Noble gases in Group 18Noble gases in Group 18
7 Diatomic Elements - BrINClHOF7 Diatomic Elements - BrINClHOF AllotropesAllotropes – Two different structures of – Two different structures of
the same elementthe same element Example – CarbonExample – Carbon
GraphiteGraphite diamonddiamond buckyballsbuckyballs
Buckyball
ElectronegativityElectronegativity
This is the ability to attract electronsThis is the ability to attract electrons Based on Fluorine, which is 4.0Based on Fluorine, which is 4.0 F has the greatest electronegativityF has the greatest electronegativity
(Foxy Fluorine steals other elements (Foxy Fluorine steals other elements electrons!)electrons!)
Ionization EnergyIonization Energy
The first ionization energy (The first ionization energy (II11) is the ) is the ENERGY needed to remove the first ENERGY needed to remove the first electron in a neutral atom. The second electron in a neutral atom. The second ionization energy (ionization energy (II22) is the energy ) is the energy needed to remove the second electron needed to remove the second electron and so on.and so on.
Measured in kJ/molMeasured in kJ/mol The greater the ionization energy the The greater the ionization energy the
more difficult it is to remove an electron.more difficult it is to remove an electron.
Trends Trends in the in the
Periodic TablePeriodic Table
Trends of Atomic RadiiTrends of Atomic Radii(across a period)(across a period)
The trend increases from LEFT to RIGHTThe trend increases from LEFT to RIGHT The radius decreases because the pulling The radius decreases because the pulling
power of the nucleus increases (due to an power of the nucleus increases (due to an increase in the effective nuclear charge.)increase in the effective nuclear charge.)
Na Al Si P
Radius = 190 Radius = 143
Radius = 132 Radius = 128
Atomic # 11
Atomic # 13
Atomic # 14
Atomic # 15
Trend in Atomic Radii
Trends in Atomic RadiiTrends in Atomic Radii(down a group)(down a group)
As you go down (↓) a group, the As you go down (↓) a group, the atomic radius increases.atomic radius increases.
Li 155
Na 190
K 235
Rb 240
Because . . . There is an increase in principal quantum numbers (n).
Na 2e-8e-
1e-
2e-
8e-
Sodium atom with 11 electrons (Na 0)
Radius = 190 pm
Sodium ion with 10 electrons (Na +1)
Radius = 120 pm
Radii of Neutral Atom versus Its Ion
1 e- removed
F 2e-7e-
2e-
8e-
Fluorine atom with 9 electrons (F 0)
Radius = 57 pm
Fluorine ion with 10 electrons (F -
1)
Radius = 95 pm
Radii of Neutral Atom versus Its Ion
1 e- added
F
The difference between the non-bonding atomic radius and the bonding atomic radius.
The bonding atomic radius is shorter than the non-bonding radius.
Atomic Radii and Bond Atomic Radii and Bond LengthsLengths
Knowing atomic radii allows us to Knowing atomic radii allows us to estimate the bond lengths between estimate the bond lengths between different atoms in molecules.different atoms in molecules.
Ex: The ClEx: The Cl � � Cl bond length in ClCl bond length in Cl22 is is 1.99 1.99 Å, Å, so a radius of 0.99Å is so a radius of 0.99Å is assigned to Cl. In CCl4, the assigned to Cl. In CCl4, the measured length of the measured length of the CC � � Cl is Cl is 1.77Å, close to the sum of the atomic 1.77Å, close to the sum of the atomic radii of C and Cl (0.77Å + 0.99Å).radii of C and Cl (0.77Å + 0.99Å).
Isoelectronic SeriesIsoelectronic Series
This is a group of ions all containing This is a group of ions all containing the same number of electrons.the same number of electrons.
The series: OThe series: O-2-2, F, F--, Na, Na++, Mg, Mg2+2+, and , and AlAl3+ 3+ all have 10 electrons.all have 10 electrons.
Nuclear charges increase as you Nuclear charges increase as you move through a series, and the move through a series, and the atomic radius of the ion decreases.atomic radius of the ion decreases.
Trends of Electronegativity Trends of Electronegativity and Ionization Energyand Ionization Energy
(across a period)
Electronegativity INCREASESIonization Energy INCREASES
WHY
?
The increased effective nuclear charge makes it harder to remove electrons.
Trends of Electronegativity Trends of Electronegativity and Ionization Energyand Ionization Energy
(down a group)
Electronegativity
DECREASES
Ionization Energy
DECREASES
WHY?
Electrons are held less tightly because energy levels increase and there is more electron shielding.
Electron AffinityElectron Affinity Most atoms gain electrons to form Most atoms gain electrons to form
anions. The energy change that anions. The energy change that occurs when an electron is added to an occurs when an electron is added to an atom is called electron affinity because atom is called electron affinity because it measures the attraction (or affinity) it measures the attraction (or affinity) of the atom for the added electron.of the atom for the added electron.
For most atoms, energy is For most atoms, energy is releasedreleased when electrons are added.when electrons are added.
Cl(Cl(gg) + e) + e-- → → ClCl--((gg)) ΔΔE = E = --349 kJ/mol349 kJ/mol
Trends of Metallic Trends of Metallic CharacteristicsCharacteristics
Across a period –
DECREASE
In metallic character
Down a group –
INCREASE
in metallic character
(There is an increased
attraction for electrons.)
(There is a decreased
attraction for electrons.)
Metallic CharacterMetallic Character
Metals have low ionization energies and Metals have low ionization energies and therefore tend to form positive ions easily. therefore tend to form positive ions easily.
As a result, metals are oxidized (lose As a result, metals are oxidized (lose electrons – LEO) when they undergo electrons – LEO) when they undergo chemical reactions.chemical reactions.
Most metal oxides are basic. Those that Most metal oxides are basic. Those that dissolve in water react to form metal dissolve in water react to form metal hydroxides.hydroxides.
CaO (CaO (ss) + HOH ) + HOH →→Ca(OH)Ca(OH)22 ( (aqaq))