Chapter 13Chapter 13

Chemical Periodicity Chemical Periodicity

IntroductionIntroduction

In the 19th century, chemists began In the 19th century, chemists began to categorize the elements according to categorize the elements according to similarities in their physical and to similarities in their physical and chemical propertieschemical properties The end result of this was the modern The end result of this was the modern

periodic tableperiodic table The periodic table is very useful for The periodic table is very useful for

understanding and predicting the understanding and predicting the properties of elementsproperties of elements

13.1 The Development of 13.1 The Development of the Periodic Tablethe Periodic Table

Newland, an English chemist, published list Newland, an English chemist, published list of elements of elements arranged in order according arranged in order according to their increasing atomic massto their increasing atomic mass..

He stated that the He stated that the elements properties elements properties repeated when they were arranged repeated when they were arranged according to increasing atomic mass in according to increasing atomic mass in groups of eightgroups of eight He called this the arrangement the law of He called this the arrangement the law of

octavesoctaves Similar to musical scale that repeats every eighth Similar to musical scale that repeats every eighth

notenote Law only works up to CaLaw only works up to Ca

13.1 The Development of 13.1 The Development of the Periodic Tablethe Periodic Table

Mendeleev, a Russian chemist, Mendeleev, a Russian chemist, refined and added to the refined and added to the arrangement of elements in a arrangement of elements in a tabletable according to their atomic according to their atomic massesmasses With this arrangement he noticed a With this arrangement he noticed a

regular (periodic) recurrence of their regular (periodic) recurrence of their physical and chemical propertiesphysical and chemical properties

13.1 The Development of 13.1 The Development of the Periodic Tablethe Periodic Table

Mosely rearranged the periodic Mosely rearranged the periodic table according to the atomic table according to the atomic number of the elements, which is number of the elements, which is how the modern periodic table is how the modern periodic table is arranged todayarranged today The periodic table is a valuable The periodic table is a valuable

organizational tool for chemists organizational tool for chemists

13.2 The Modern 13.2 The Modern Periodic TablePeriodic Table

The most commonly used modern The most commonly used modern periodic table, sometimes called the periodic table, sometimes called the long form (your table)long form (your table)

The long form table lists many The long form table lists many properties of the elements so that properties of the elements so that the chemist can check them at a the chemist can check them at a glanceglance

13.2 The Modern 13.2 The Modern Periodic TablePeriodic Table

The periodic law states that when The periodic law states that when elements are arranged in order of elements are arranged in order of increasing atomic number, there is a increasing atomic number, there is a periodic pattern in their physical and periodic pattern in their physical and chemical propertieschemical properties

The horizontal rows of the periodic The horizontal rows of the periodic table are called table are called periodsperiods – – there are there are 7 periods in the periodic table7 periods in the periodic table

13.2 The Modern 13.2 The Modern Periodic TablePeriodic Table

The vertical columns are called The vertical columns are called groupsgroups or or familiesfamilies identified by number identified by number and a letterand a letter Groups 1A through 7A and group 0 make Groups 1A through 7A and group 0 make

up the up the representative elementsrepresentative elements (wide (wide variety of properties)variety of properties)

Group B elements are the Group B elements are the transition transition metalsmetals

Two rows of elements below the periodic Two rows of elements below the periodic table are the table are the lanthanideslanthanides and and actinidesactinides

13.3 Electron 13.3 Electron Configurations and Configurations and

Periodicity Periodicity The The electron configurationelectron configuration of an element of an element

plays the plays the greatest part in determining it’s greatest part in determining it’s physical and chemical properties physical and chemical properties

Most elements within the same group have Most elements within the same group have the identical electron configurations in their the identical electron configurations in their outer most energy level (outer most energy level (valence levelvalence level))

Elements are classified into 4 different Elements are classified into 4 different categories according to their valence (outer) categories according to their valence (outer) electron configurationelectron configuration Noble Gases, Representative Elements, Transition Noble Gases, Representative Elements, Transition

Metals, Inner Transition MetalsMetals, Inner Transition Metals

13.3 Noble Gases (Group 13.3 Noble Gases (Group 0)0)

1. 1. Noble gasesNoble gases (group 0) are elements in (group 0) are elements in which which the outermost s and p the outermost s and p sublevels are filledsublevels are filled Also called Also called inert gasesinert gases because they do not because they do not

react with other elements – they are stable react with other elements – they are stable on their ownon their own

Helium has 2 valence electronsHelium has 2 valence electrons (full 1s (full 1s sublevel)sublevel)

The rest of the The rest of the noble gases have 8 noble gases have 8 valence electronsvalence electrons (full s and p sublevels): (full s and p sublevels): Ne, Ar, Kr, Xe, Rn Ne, Ar, Kr, Xe, Rn

13.3 Representative 13.3 Representative ElementsElements

2. Representative elements (Group A) 2. Representative elements (Group A) Elements whose outermost s or p Elements whose outermost s or p

sublevels are only partially filledsublevels are only partially filled Group 1A are known as the Group 1A are known as the alkali alkali

metals metals 1 electron in outermost energy level 1 electron in outermost energy level Very reactive → only in compounds in Very reactive → only in compounds in

naturenature

13.3 Representative 13.3 Representative ElementsElements

2. Representative elements (Group A) 2. Representative elements (Group A) continuedcontinued

Group 2A are known as the Group 2A are known as the alkaline earth alkaline earth metalsmetals 2 electrons in outermost energy level2 electrons in outermost energy level Also reactive (but not as reactive as 1A) → only Also reactive (but not as reactive as 1A) → only

in compounds in naturein compounds in nature Group 7A are known as the Group 7A are known as the halogenshalogens

7 electrons in outermost energy level 7 electrons in outermost energy level Nonmetals that are highly reactive Nonmetals that are highly reactive Also called salt formers Also called salt formers

13.3 Representative 13.3 Representative ElementsElements

For any representative element, For any representative element, the the group number is equal to the group number is equal to the number of electrons in the number of electrons in the outermost energy level outermost energy level See periodic table 354 –355See periodic table 354 –355

13.3 Transition Elements13.3 Transition Elements

3. Transition Metals (Group B) 3. Transition Metals (Group B) Elements whose outermost s sublevel Elements whose outermost s sublevel

and nearby d sublevel contain and nearby d sublevel contain electrons electrons The d sublevels overlap with s sublevels The d sublevels overlap with s sublevels

– this is why they are transition elements– this is why they are transition elements Characterized by having electrons added Characterized by having electrons added

to the d orbitalsto the d orbitals Not as reactive as Group A elementsNot as reactive as Group A elements

13.3 Inner Transition 13.3 Inner Transition MetalsMetals

4. Inner Transition Metals4. Inner Transition Metals Elements whose outermost s Elements whose outermost s

sublevel and nearby f sublevel sublevel and nearby f sublevel generally contain electronsgenerally contain electrons

Characterized by the filling of the f Characterized by the filling of the f orbitals orbitals

13.3 Electron 13.3 Electron Configurations and Configurations and

PeriodicityPeriodicity The periodic table can be divided into The periodic table can be divided into

sections, which correspond to the sections, which correspond to the sublevels that are filled with electrons sublevels that are filled with electrons (on your table) (blocks)(on your table) (blocks)

Group1A and 2A are in the s block Group1A and 2A are in the s block (also Helium)(also Helium) valence level = period # valence level = period #

Group 3A, 4A, 5A, 6A, 7A, and 0 Group 3A, 4A, 5A, 6A, 7A, and 0 belong to p block belong to p block valence level = period #valence level = period #

13.3 Electron 13.3 Electron Configurations and Configurations and

PeriodicityPeriodicity Transition belong to d block Transition belong to d block

Exception – d sublevel is one less than period Exception – d sublevel is one less than period ##

Inner transition belong to f block Inner transition belong to f block Exception – f sublevel is 2 less than period #Exception – f sublevel is 2 less than period #

The valence electron configurations can The valence electron configurations can be determined by using the block be determined by using the block diagram in figure 13.4 – on your periodic diagram in figure 13.4 – on your periodic tabletable

13.4 Periodic Trends in 13.4 Periodic Trends in Atomic SizeAtomic Size

Remember that, according to the Remember that, according to the quantum mechanical model, an atom quantum mechanical model, an atom does not have a specifically defined does not have a specifically defined boundary that sets the limit of its boundary that sets the limit of its size.size.

13.4 Periodic Trends in 13.4 Periodic Trends in Atomic SizeAtomic Size

However, there are ways to estimate However, there are ways to estimate the relative sizes of atoms.the relative sizes of atoms. X-ray diffraction – estimates the size of X-ray diffraction – estimates the size of

atoms in crystalline solidsatoms in crystalline solids The distance between the nuclei of The distance between the nuclei of

diatomic molecules (examples: Odiatomic molecules (examples: O22 or Br or Br22) ) can be used to estimate the can be used to estimate the atomic atomic radiusradius of an atom. of an atom.

atomic radiusatomic radius – half the distance between – half the distance between the nuclei of two like atomsthe nuclei of two like atoms

13.4 Atomic Size – Group 13.4 Atomic Size – Group TrendsTrends

Atomic size generally increases as Atomic size generally increases as you move down a group of the you move down a group of the periodic tableperiodic table

The size increases because electrons The size increases because electrons are added to higher principle energy are added to higher principle energy levels levels The added charge of nucleus pulls The added charge of nucleus pulls

electrons inward, but the electrons inward, but the net effectnet effect is an is an increase in size because electrons are increase in size because electrons are further from nucleusfurther from nucleus

13.4 Atomic Size – Periodic 13.4 Atomic Size – Periodic TrendsTrends

Atomic size generally decreases as you Atomic size generally decreases as you move from left to right across a period move from left to right across a period

The size decreases because electrons are The size decreases because electrons are added to the same principle energy level, added to the same principle energy level, but the added charge of nucleus pulls but the added charge of nucleus pulls electrons inward; the electrons inward; the net effectnet effect is a is a decrease in sizedecrease in size This trend is less pronounced in periods where This trend is less pronounced in periods where

there are more electrons in the occupied there are more electrons in the occupied principle energy levels between the nucleus principle energy levels between the nucleus and the outermost electrons; this is referred to and the outermost electrons; this is referred to as the as the shielding effectshielding effect

13.5 Periodic Trends in 13.5 Periodic Trends in Ionization EnergyIonization Energy

When an atom gains or loses an electron When an atom gains or loses an electron it forms an ion.it forms an ion.

The energy that is required to overcome the The energy that is required to overcome the attraction of the nuclear charge and remove attraction of the nuclear charge and remove an electron from a gaseous atom is called the an electron from a gaseous atom is called the ionization energyionization energy The first ionization energy is the amount needed The first ionization energy is the amount needed

to remove the first outermost electron to remove the first outermost electron The second ionization energy is the amount The second ionization energy is the amount

needed to remove the next outermost electron needed to remove the next outermost electron The third ionization energy is the amount to The third ionization energy is the amount to

remove the third and so on (Table 13.1 page 362)remove the third and so on (Table 13.1 page 362)

13.5 Periodic Trends in 13.5 Periodic Trends in Ionization EnergyIonization Energy

Ionization energies can be used to Ionization energies can be used to predict how many electrons an atom predict how many electrons an atom will gain or lose in a chemical will gain or lose in a chemical reaction reaction 1A vs. 2A – Table 13.1 page 3621A vs. 2A – Table 13.1 page 362

Two factors affect ionization energy: Two factors affect ionization energy: nuclear chargenuclear charge and and distance from distance from the nucleusthe nucleus

13.5 13.5 Ionization Energy – Group Ionization Energy – Group TrendsTrends

In general, the first ionization In general, the first ionization energy decreases as you move energy decreases as you move down a group on the periodic down a group on the periodic table.table. The size of the atoms increases as you The size of the atoms increases as you

move down; thus the outermost move down; thus the outermost electron is farther from the nucleus and electron is farther from the nucleus and more easily removed more easily removed This results in a lower ionization energyThis results in a lower ionization energy

13.5 13.5 Ionization Energy – Ionization Energy – Periodic TrendsPeriodic Trends

For the representative elements, For the representative elements, the first ionization energy the first ionization energy generally increases as you move generally increases as you move from left to right across a period.from left to right across a period. The nuclear charge is increasing and The nuclear charge is increasing and

the atomic size is decreasing, therefore the atomic size is decreasing, therefore there is more of an attraction between there is more of an attraction between the nucleus and the outermost electronthe nucleus and the outermost electron This results in a higher ionization energyThis results in a higher ionization energy

13.6 Trends in Ionic Size13.6 Trends in Ionic Size

When atoms lose electrons they When atoms lose electrons they become become positive ionspositive ions ( (cationscations))

Cations are always Cations are always smallersmaller than the than the atoms from which they are formedatoms from which they are formed There is a There is a stronger attractionstronger attraction

between the nucleus (same number of between the nucleus (same number of protons) and the remaining electrons protons) and the remaining electrons (fewer)(fewer)

13.6 Trends in Ionic Size13.6 Trends in Ionic Size

When atoms gain electrons they When atoms gain electrons they become become negative ionsnegative ions ( (anionsanions))

Anions are always Anions are always largerlarger than the than the atoms from which they are formedatoms from which they are formed There is less of an attraction between There is less of an attraction between

the nucleus (same number of protons) the nucleus (same number of protons) and the resulting electrons (more)and the resulting electrons (more)

13.6 Trends in Ionic Size13.6 Trends in Ionic Size

Periodic TrendPeriodic Trend – There is a – There is a decrease in the size of cations as you decrease in the size of cations as you move across a period from left to move across a period from left to right – when you get to group 4A the right – when you get to group 4A the anions (which are much larger) start anions (which are much larger) start to decrease in sizeto decrease in size

Group TrendGroup Trend – Ionic size (both – Ionic size (both cations and anions) increases as you cations and anions) increases as you go down each group.go down each group.

13.7 Trends in 13.7 Trends in ElectronegativityElectronegativity

The The electronegativityelectronegativity of an element is of an element is the tendency for the atoms of the the tendency for the atoms of the element to attract electrons when they element to attract electrons when they are chemically combined with another are chemically combined with another elementelement The Pauling scale uses arbitrary units to The Pauling scale uses arbitrary units to

express the electronegativity of the all express the electronegativity of the all elements (except noble gases)elements (except noble gases) The Pauling scale is based on a number of The Pauling scale is based on a number of

factors including ionization energies and factors including ionization energies and electron affinitieselectron affinities

13.7 Trends in 13.7 Trends in ElectronegativityElectronegativity

Periodic TrendPeriodic Trend – As you go across a period – As you go across a period from left to right, the electronegativity of the from left to right, the electronegativity of the representative elements increasesrepresentative elements increases Metallic elements far left have low Metallic elements far left have low

electronegativitieselectronegativities Nonmetallic elements far right have high Nonmetallic elements far right have high

electronegativitieselectronegativities Group TrendGroup Trend - Electronegativity generally - Electronegativity generally

decreases as you go down a groupdecreases as you go down a group*Transition metals do not show as regular trend of *Transition metals do not show as regular trend of

electronegativityelectronegativity