PeriodicityPeriodicity

General info.General info.

Periodicity is concerned with trends or patterns Periodicity is concerned with trends or patterns seen within elements on the periodic table.seen within elements on the periodic table.

The patterns that will be covered are:The patterns that will be covered are: Atomic radiusAtomic radius Ionization energyIonization energy ElectronegativityElectronegativity Melting points (IB/SL only)Melting points (IB/SL only) Period 3 (IB/SL onlyPeriod 3 (IB/SL only

Atomic radiusAtomic radius

Remember, the radius is determined Remember, the radius is determined directly by the electron clouddirectly by the electron cloud

Atomic radiiAtomic radii Going down a group (column)Going down a group (column) The radius increases going down a group.The radius increases going down a group. This increase is due to the addition of This increase is due to the addition of

energy levels. Each e.l. increases the energy levels. Each e.l. increases the electron cloud significantly. electron cloud significantly.

Going across a period.Going across a period. The radius decreases going across a period.The radius decreases going across a period.

The nucleus increases, which means there is a The nucleus increases, which means there is a greater positive charge present. This increase in greater positive charge present. This increase in positive charge pulls the electrons in closer to the positive charge pulls the electrons in closer to the nucleus, thus, reducing the radius.nucleus, thus, reducing the radius.

No energy levels are being added.No energy levels are being added.

Chart of atomic radiiChart of atomic radii

Chart showing radius Chart showing radius trends across several trends across several periods periods

Atomic radii with d block Atomic radii with d block elementselements

Ionic radiiIonic radii

The radius of an atom increases when an The radius of an atom increases when an electron is added to make a (-) ion electron is added to make a (-) ion (anion).(anion).

Anions have more e- than protons so the Anions have more e- than protons so the additonal e- is not pulled in close to the additonal e- is not pulled in close to the nucleus. This causes the e- cloud to nucleus. This causes the e- cloud to expand.expand.

Ionic radii continuedIonic radii continued

The radius of an atom decreases when an The radius of an atom decreases when an electron is lost to make a (+) ion (cation).electron is lost to make a (+) ion (cation).

Cations have more protons than electrons, so Cations have more protons than electrons, so the electrons now have a stronger pull on them the electrons now have a stronger pull on them from the nucleus, thus shrinking the e- cloud.from the nucleus, thus shrinking the e- cloud.

Also, usually when atoms lose any e-, it is all of Also, usually when atoms lose any e-, it is all of the valence e- they lose, so the entire energy the valence e- they lose, so the entire energy level is lost. This really decreases the e- cloud.level is lost. This really decreases the e- cloud.

Transitional metals do not lose an e.l.Transitional metals do not lose an e.l.

Metal ionic radiiMetal ionic radii

Nonmetal ionic radiiNonmetal ionic radii

Ionic radii chartsIonic radii charts

Ionization energy (IE)Ionization energy (IE)

Ionization energy- the energy required to remove an Ionization energy- the energy required to remove an electron from a gaseous atom.electron from a gaseous atom.

Since the electrons are attracted to the nucleus, it Since the electrons are attracted to the nucleus, it takes energy to pull the e- from the atom.takes energy to pull the e- from the atom.

Electrons in the last e.l. are the electrons that are being Electrons in the last e.l. are the electrons that are being removed. These electrons are called removed. These electrons are called valence valence electrons. D-block elements have their valence e- electrons. D-block elements have their valence e- in the last two energy levels.in the last two energy levels.

First ionization energy. The energy required to remove First ionization energy. The energy required to remove the first valence electron from a neutral atom.the first valence electron from a neutral atom.

Trends in the first Trends in the first ionization energyionization energy

Going down a groupGoing down a group The first ionization energy decreases.The first ionization energy decreases.

The radius is increasing and the further away an e- is from The radius is increasing and the further away an e- is from the nucleus, the less pull (attractive force) there is on the the nucleus, the less pull (attractive force) there is on the electron. electron.

The further away an e- is from the nucleus, there are more The further away an e- is from the nucleus, there are more e- (core e-) between the nucleus and the valence e-, thus e- (core e-) between the nucleus and the valence e-, thus weakening the pull from nucleus. (this is called shielding.)weakening the pull from nucleus. (this is called shielding.)

With the addition of each new energy level the valence With the addition of each new energy level the valence electrons become further away from the nucleus.electrons become further away from the nucleus.

Going across a periodGoing across a period The first ionization energy increasesThe first ionization energy increases

The atomic radius decreases. The valence e- The atomic radius decreases. The valence e- become closer to the nucleus going from left to become closer to the nucleus going from left to right , therefore there is a stronger pull (attractive right , therefore there is a stronger pull (attractive force) from the nucleus on the valence e-. So, force) from the nucleus on the valence e-. So, more energy is required to remove an electron. more energy is required to remove an electron.

3-d chart on first 3-d chart on first ionization energiesionization energies

First ionization energy First ionization energy trends across several trends across several periods.periods.

Successive ionization Successive ionization energies (IE)energies (IE)

The energy required to remove the first e- The energy required to remove the first e- from an atom is the 1from an atom is the 1stst ionization energy. ionization energy.

The energy required to remove a 2The energy required to remove a 2ndnd e- is e- is the 2the 2ndnd ionization energy and so on. ionization energy and so on.

The energy required to remove an e- The energy required to remove an e- increases with each successive e-. For increases with each successive e-. For example: Al: IEexample: Al: IE11= 577 IE= 577 IE22= 1815, = 1815, IEIE33=2740 all in kJ/mole =2740 all in kJ/mole

Succesive ionization Succesive ionization energies cont.energies cont.

Successive ionization energies increase Successive ionization energies increase because.because. After each e- is removed, the radius After each e- is removed, the radius

becomes smaller making the remaining e- becomes smaller making the remaining e- closer to the nucleus.closer to the nucleus.

There are more protons than e-, making the There are more protons than e-, making the attractive force from the nucleus stronger on attractive force from the nucleus stronger on the core e-.the core e-.

Successive ionization Successive ionization energies cont.energies cont.

After all of the valence e- have been After all of the valence e- have been removed from an atom, there is a huge removed from an atom, there is a huge increase in the IE. increase in the IE. IE for core e- are extremely high due to them IE for core e- are extremely high due to them

being in a lower e.l. that is closer to the being in a lower e.l. that is closer to the nucleus.nucleus.

There are many more protons than e-.There are many more protons than e-.

Chart of succesive Chart of succesive ionization energies ( IE)ionization energies ( IE)

ElectronegativityElectronegativity

A measurement of an element’s ability to A measurement of an element’s ability to attract an electron from another atom attract an electron from another atom within a bond. When 2 atoms of different within a bond. When 2 atoms of different elements bond, one atom is better elements bond, one atom is better attracting the electrons in the bond. This attracting the electrons in the bond. This attraction is electronegativity.attraction is electronegativity.

Electronegativity Electronegativity continuedcontinued

An atom is more electronegative if:An atom is more electronegative if: The atom has a small e- cloud. The small e- The atom has a small e- cloud. The small e-

cloud allows its nucleus to get closer to cloud allows its nucleus to get closer to another atom’s electrons and pull off e-another atom’s electrons and pull off e-

Larger nucleus: more attractive force on Larger nucleus: more attractive force on another atom’s electrons.another atom’s electrons.

In summary: volume/mass ratio should In summary: volume/mass ratio should be small.be small.

Electronegativity Electronegativity continued.continued.

The most electronegative element is Fluorine. The most electronegative element is Fluorine. Fluorine is given an electronegative rating of Fluorine is given an electronegative rating of

4.0 which is the highest rating. All other 4.0 which is the highest rating. All other elements are compared to it and are given a elements are compared to it and are given a relative rating.relative rating.

The trends in electronegativity are the same as The trends in electronegativity are the same as the ionization energy: increases across a the ionization energy: increases across a period, decreases down a group.period, decreases down a group.

Chart of Chart of electronegativitieselectronegativities

Electronegative trends Electronegative trends for the first 5 periods.for the first 5 periods.

Applying periodic trends Applying periodic trends to chemical reactivityto chemical reactivity

Metals are reactive if:Metals are reactive if: ((lose e- in lose e- in

reactions)reactions) Larger radiusLarger radius Lower ionization Lower ionization

energyenergy Fewer valence e-Fewer valence e-

Nonmetals are Nonmetals are reactive if:reactive if:

(gain e- in (gain e- in reactions.)reactions.)

Smaller radiusSmaller radius High High

electronegativityelectronegativity More valence e-More valence e-

Melting point trendsMelting point trends

Down a group: The melting points tend to Down a group: The melting points tend to decrease. The large radius decreases decrease. The large radius decreases the attraction between atoms, thus, the attraction between atoms, thus, making a substance easier to melt.making a substance easier to melt.

Across a period: the melting points Across a period: the melting points increase until group 14. Then they increase until group 14. Then they decrease. decrease.

Melting points for the Melting points for the group 1 elementsgroup 1 elements

States of matter for all States of matter for all the elements at 3507 Cthe elements at 3507 C

Melting and boiling point Melting and boiling point trends for elements 1-95trends for elements 1-95

Chemical and physicial Chemical and physicial properties properties

Alkali metals:Alkali metals: Very soft metalsVery soft metals Not very dense and so float on waterNot very dense and so float on water Low melting points: Li=454K to Cs=302 KLow melting points: Li=454K to Cs=302 K One valence e- with a low ionization energy.One valence e- with a low ionization energy. Readily react with nonmetalsReadily react with nonmetals React with water to form a strong base. React with water to form a strong base.

Example:2NaExample:2Na(s)(s) + 2H + 2H22OO(l)(l) 2NaOH 2NaOH(aq)(aq) + H + H2(g)2(g)

Continued:Continued:

HalogensHalogens

HalogenHalogen FluorineFluorine ChlorineChlorine BromineBromine IodineIodine

ColorColor Pale Pale yellowyellow

Yellow Yellow greengreen

Red Red brown brown

Black or Black or purplepurple

State at State at room room temp.temp.

GasGas GasGas LiquidLiquid solidsolid

Continued: HalogensContinued: Halogens

All exist as diatomic molecules in their pure state. FAll exist as diatomic molecules in their pure state. F22, , ClCl22 Br Br22 I I22

Are nonpolar and have only van der waal forces when Are nonpolar and have only van der waal forces when in their pure form.in their pure form.

Slightly soluble in water. Slightly soluble in water. When in water they dissociate slightly:When in water they dissociate slightly: XX2 2 + H + H22O O H H++ + X + X-- + HOX, + HOX,

The HOX is a weak acid but a strong oxidant due to the The HOX is a weak acid but a strong oxidant due to the oxygen which reacts with other materials and bleaches them. oxygen which reacts with other materials and bleaches them. Example is HOCl is in bleach. These acids are also toxic to Example is HOCl is in bleach. These acids are also toxic to microbes, and so make disinfectants and are used in water microbes, and so make disinfectants and are used in water treatment.treatment.

Continued: halogensContinued: halogens

They combine with metals to produce They combine with metals to produce ionically bonded salts called hallides. Ex. ionically bonded salts called hallides. Ex. NaCl, Most are soluble in water, NaCl, Most are soluble in water, exception, AgCl, PbClexception, AgCl, PbCl22

The reactivity decreases going down the The reactivity decreases going down the group. (This is the opposite of the Alkali group. (This is the opposite of the Alkali metals.)The radius increases which metals.)The radius increases which reduces the ability of the elements to reduces the ability of the elements to attract electrons.attract electrons.

Trends in period 3Trends in period 3

Left hand side: groups 1 and 2 alkali and alkaline metals. Left hand side: groups 1 and 2 alkali and alkaline metals. Large radii, low IE, and so react as metals, losing e-Large radii, low IE, and so react as metals, losing e- React with nonmetals to make solid ionic compounds.React with nonmetals to make solid ionic compounds. These solids are crystaline solids with high melting These solids are crystaline solids with high melting

and boiling points. Ex. NaCland boiling points. Ex. NaCl The solids easily dissolve in water to form ions.The solids easily dissolve in water to form ions. Oxides, such as MgO, KOxides, such as MgO, K22O dissolve in water to form O dissolve in water to form

bases. Ex. MgO + Hbases. Ex. MgO + H22O O Mg(OH) Mg(OH)22 and can neutralize acids. ex MgO + 2HCl and can neutralize acids. ex MgO + 2HCl MgCl MgCl22 + +

HH22OO

Middle of period 3Middle of period 3 Group 3:Aluminum is a metalGroup 3:Aluminum is a metal

Its oxide is amphoteric, that is it can dissolve in either an acid Its oxide is amphoteric, that is it can dissolve in either an acid or a base. Alor a base. Al22OO33 + 6HCl + 6HCl 2AlCl 2AlCl33 + 3H + 3H22O, O,

AlAl22OO33 + 2OH + 2OH-- + 3H + 3H22OO 2Al(OH) 2Al(OH)44- -

Makes crystalline solids like AlClMakes crystalline solids like AlCl33 with high melting/boiling with high melting/boiling points.points.

Group4: Si, the ionization energy too great to behave as a metal Group4: Si, the ionization energy too great to behave as a metal and so the first nonmetal appears.and so the first nonmetal appears.

Its oxide will react with water to produce a weak acid.Its oxide will react with water to produce a weak acid. Ex. COEx. CO22 + H + H22O O H H22COCO33 (H (H++ + HCO + HCO33

--)) Make large crystalline solid networks with very high melting Make large crystalline solid networks with very high melting

a boiling points. Ex. Graphite, diamond, silicon chips.a boiling points. Ex. Graphite, diamond, silicon chips.

Group 5: Phosphorus: Makes primarily Group 5: Phosphorus: Makes primarily covalently bonded molecules. covalently bonded molecules.

Weak forces are between its molecules, Weak forces are between its molecules, with chlorine or anything else.with chlorine or anything else.

Very low melting and boiling points.Very low melting and boiling points. Oxides form acid in water (versions of Oxides form acid in water (versions of

phosphoric acid.) Hphosphoric acid.) H33POPO44

Group 6 Sulfur. Group 6 Sulfur. Makes covalent compounds with weak Makes covalent compounds with weak

intermolecular forces, low melting/boiling intermolecular forces, low melting/boiling points.points.

Oxides dissolve to form acid in water:Oxides dissolve to form acid in water: SOSO2 2 + H+ H22O O H H22SOSO3 3

or SOor SO33 + H + H22O O H H22SOSO44

Group 7:HalogensGroup 7:Halogens Are nonmetals that exist as diatomic Are nonmetals that exist as diatomic

molecules.molecules. FF22, Cl, Cl22, are gases, Br, are gases, Br2 2 liquid, Iliquid, I22 solid. Only van solid. Only van

der waal forces exist between molecules.der waal forces exist between molecules. These elements combine with metals to make These elements combine with metals to make

water soluble ionic compounds that have high water soluble ionic compounds that have high melting and boiling points. (Silver compounds melting and boiling points. (Silver compounds are not water soluble.)are not water soluble.)

Reactions are in previous slide. Reactions are in previous slide.

Summary of period 3: Summary of period 3: trends seen.trends seen.

Metal or nonmetal: Metallic Metal or nonmetal: Metallic nonmetallic nonmetallic Physical state in pure form: solidPhysical state in pure form: solidgas.gas. Pure element combines with water: bases Pure element combines with water: bases to to

acidsacids Oxides react with water to form: basesOxides react with water to form: bases

amphoteric amphoteric acids, oxidants or bleaches. acids, oxidants or bleaches. Compounds: crystalline solids (groups 1,2) Compounds: crystalline solids (groups 1,2)

strong networks (group 4) strong networks (group 4) weak molecular weak molecular solids (groups 5,6) solids (groups 5,6) gases (group7) gases (group7) exception is iodineexception is iodine