Periodic LawPeriodic Law

Periodic TablePeriodic Table

Prior to 1860 no agreement/method to Prior to 1860 no agreement/method to accurately determine masses of atoms.accurately determine masses of atoms.

First International Congress of First International Congress of Chemists – 1860Chemists – 1860 Stanislao Cannizzaro presented method Stanislao Cannizzaro presented method

for accurately measuring atomic massesfor accurately measuring atomic masses Looked for relationships between atomic Looked for relationships between atomic

masses and other properties of elementsmasses and other properties of elements

First tables arranged elements by First tables arranged elements by atomic weight atomic weight Could not agree on atomic weights Could not agree on atomic weights

therefore tables were differenttherefore tables were different

John NewlandsJohn Newlands

Noticed elements properties Noticed elements properties repeated every 8repeated every 8thth element when element when arranged by atomic massarranged by atomic mass

Named this phenomenon “Named this phenomenon “the Law of the Law of OctavesOctaves””

Did not work for all elementsDid not work for all elements

Julius Lothar MeyerJulius Lothar Meyer Developed first modern Developed first modern

tabletable Consisted of 28 elements Consisted of 28 elements

divided into 6 familiesdivided into 6 families Families (groups) had Families (groups) had

similar chemical and similar chemical and physical propertiesphysical properties

Discovered all elements in Discovered all elements in same family had same same family had same number of number of valence evalence e- - -- -- outermost electrons in outermost electrons in highest energy levelhighest energy level

Why?Why?

Dmitri MendeleevDmitri Mendeleev Noticed that properties Noticed that properties

repeat themselves at repeat themselves at certain intervalscertain intervals

Arranged all Arranged all knownknown elements into one table elements into one table based on properties– 1869based on properties– 1869

1871 - Proposed the 1871 - Proposed the “Periodic Law” “Periodic Law”

Based on the properties Based on the properties spaces were left for spaces were left for unknown elements (Sc, unknown elements (Sc, Ga, Ge)Ga, Ge)

Upon discovery of other elements Upon discovery of other elements inconsistencies were found with inconsistencies were found with Mendeleev’s tableMendeleev’s table

Atomic masses improved and they Atomic masses improved and they no longer arranged the elements by no longer arranged the elements by increasing atomic massincreasing atomic mass

Why can most elements be arranged Why can most elements be arranged by atomic mass?by atomic mass?

What was the reason for chemical What was the reason for chemical periodicity?periodicity?

Henry MoselyHenry Mosely

Discovered elements contain unique Discovered elements contain unique number of protons (atomic number) - number of protons (atomic number) - 19111911

Arranged elements by atomic Arranged elements by atomic number - 1913number - 1913

Fully explained the Periodic LawFully explained the Periodic Law

Periodic LawPeriodic Law

The physical and chemical The physical and chemical properties of the elements are properties of the elements are periodic functions of their atomic periodic functions of their atomic numbers.numbers.

Aka – when elements are arranged Aka – when elements are arranged by increasing atomic number, by increasing atomic number, elements with similar properties elements with similar properties appear at regular intervals.appear at regular intervals.

Parts of the Periodic Parts of the Periodic TableTable

Noble Gases – added to the table in Noble Gases – added to the table in 1894 after the discovery by Lord 1894 after the discovery by Lord Rayleigh and William Ramsey Rayleigh and William Ramsey First discovered Argon while studying First discovered Argon while studying

nitrogen nitrogen Later discovered HeliumLater discovered Helium Highly inert (unreactive) due to a full Highly inert (unreactive) due to a full

octet octet

Parts….Parts….

Alkali metals – group 1Alkali metals – group 1 Alkaline earth metals – group 2Alkaline earth metals – group 2 Halogens – group 17Halogens – group 17 Transition metals – d block elementsTransition metals – d block elements Inner Transition metalsInner Transition metals

Lanthanides (elements 58-71) added in Lanthanides (elements 58-71) added in early 1900’s early 1900’s

Have very similar propertiesHave very similar properties Actinides (elements 90-103)Actinides (elements 90-103)

Electron Electron Configuration & Configuration &

the Periodic the Periodic TableTable

s-Block Elementss-Block Elements

Groups 1 & 2Groups 1 & 2 All elements in group 1 & 2 will have All elements in group 1 & 2 will have

an electron configuration of an electron configuration of nnss11 or or nnss22 where n = highest energy where n = highest energy

level occupiedlevel occupied

Alkali MetalsAlkali Metals

Group 1 elementsGroup 1 elements In the elemental stateIn the elemental state

SoftSoft Silvery metalSilvery metal High melting pointsHigh melting points Extremely reactive therefore are not Extremely reactive therefore are not

found in elemental state in naturefound in elemental state in nature React violently with React violently with water to to

produce hydrogen gas hydrogen gas

Alkaline – Earth MetalsAlkaline – Earth Metals

Group 2 elementsGroup 2 elements Outer most s orbital is full Outer most s orbital is full

Do not exhibit stability (outer p orbital Do not exhibit stability (outer p orbital is empty)is empty)

PropertiesProperties Harder, denser than group 1Harder, denser than group 1 Higher melting points than group 1Higher melting points than group 1 Not as reactive but too reactive to be Not as reactive but too reactive to be

found in nature in elemental formfound in nature in elemental form

Burning MgBurning Mg

Hydrogen & HeliumHydrogen & Helium

H has same valence electrons as H has same valence electrons as group 1 but does not share any other group 1 but does not share any other propertiesproperties

He share same electron He share same electron configuration (valence econfiguration (valence e--) as group 2 ) as group 2 but does not share same propertiesbut does not share same properties Placed with group 18 because it is very Placed with group 18 because it is very

stablestable

d-block elementsd-block elements

Transition elements Transition elements Beginning filling the 3d orbitalsBeginning filling the 3d orbitals Good conductors of electricityGood conductors of electricity High lusterHigh luster Less reactive than s-block elementsLess reactive than s-block elements

Can be found in elemental formCan be found in elemental form

Exceptions in the d-blockExceptions in the d-block

The following elements have odd The following elements have odd configurationsconfigurations Cr: [Ar]4sCr: [Ar]4s113d3d55

Cu: [Ar]4sCu: [Ar]4s113d3d1010

Ag: [Kr]5sAg: [Kr]5s114d4d1010

More stable with half filled s & d orbitals More stable with half filled s & d orbitals or full d orbitalor full d orbital

Exceptions follow throughout the d Exceptions follow throughout the d element similar to Chromium and Copperelement similar to Chromium and Copper

p-block elementsp-block elements

All elements in p block have a full s orbitalAll elements in p block have a full s orbital PropertiesProperties

Contain all non metals except H & HeContain all non metals except H & He Contain all metalloids (exhibit properties of Contain all metalloids (exhibit properties of

both metals and non metals)both metals and non metals) Have semi conducting propertiesHave semi conducting properties

Contains 6 metalsContains 6 metals

Elements in s & p block make up the Elements in s & p block make up the representative elementsrepresentative elements

HalogensHalogens

Group 7A/17Group 7A/17 Most reactive non metals (Fluorine is Most reactive non metals (Fluorine is

most reactive)most reactive) Will bond with a metal to form a saltWill bond with a metal to form a salt F & Cl are gases at room tempF & Cl are gases at room temp Br is a liquid at room tempBr is a liquid at room temp I & At are solids at room tempI & At are solids at room temp

Periodic TrendsPeriodic Trends

Octet RuleOctet Rule

Atoms will gain, lose, or share Atoms will gain, lose, or share electrons in order to have eight (8) electrons in order to have eight (8) valence electrons.valence electrons. 3 or less valence electrons – atom likely 3 or less valence electrons – atom likely

to lose electronsto lose electrons 6 or more valence electrons – atoms 6 or more valence electrons – atoms

likely to gain electronslikely to gain electrons 4 or 5 valence electrons – atoms likely 4 or 5 valence electrons – atoms likely

to share electronsto share electrons

Periodic TrendsPeriodic Trends

Properties of the elements change in Properties of the elements change in a predictable manner across a a predictable manner across a period and down a groupperiod and down a group

Atomic RadiusAtomic Radius

The half distance The half distance between nuclei of between nuclei of identical atoms identical atoms that are chemically that are chemically bonded togetherbonded together

Atomic RadiusAtomic Radius

Tends to decrease as you go across a Tends to decrease as you go across a period period Increase nuclear charge pulls electrons Increase nuclear charge pulls electrons

closer to the nucleus (decreasing radius) Zcloser to the nucleus (decreasing radius) Zeffeff

Tends to increase as you go down a Tends to increase as you go down a groupgroup New electrons are placed in higher energy New electrons are placed in higher energy

levelslevels Shielding: core electrons shield outer Shielding: core electrons shield outer

electrons from pull from nucleuselectrons from pull from nucleus

Ionic RadiusIonic Radius

Ions – atom or bonded group of Ions – atom or bonded group of atoms that has a positive or negative atoms that has a positive or negative charge due to a loss/gain of charge due to a loss/gain of electronselectrons Positive charge Positive charge lost electrons lost electrons

Smaller ionic radius compared to anionsSmaller ionic radius compared to anions Negative charge Negative charge gained electrons gained electrons

Larger ionic radius compared to cationsLarger ionic radius compared to cations

Ionic RadiusIonic Radius

Tends to decrease across a periodTends to decrease across a period Tends to increase down a groupTends to increase down a group

Ionic Radius vs. Atomic Ionic Radius vs. Atomic RadiusRadius

Metals - the atomic radius of a metal is Metals - the atomic radius of a metal is generally larger than the ionic radius of the generally larger than the ionic radius of the same element. same element.

WhyWhy? Generally, metals loose electrons to achieve ? Generally, metals loose electrons to achieve the octet. This creates a larger positive charge in the octet. This creates a larger positive charge in the nucleus than the negative charge in the the nucleus than the negative charge in the electron cloud, causing the electron cloud to be electron cloud, causing the electron cloud to be drawn a little closer to the nucleus as an ion.drawn a little closer to the nucleus as an ion.

Ionic Radius vs. Atomic Ionic Radius vs. Atomic Radius cont.Radius cont.

Non-metals - the atomic radius of a Non-metals - the atomic radius of a non-metal is generally smaller than non-metal is generally smaller than the ionic radius of the same element. the ionic radius of the same element.

WhyWhy? Generally, non-metals loose ? Generally, non-metals loose electrons to achieve the octet. This electrons to achieve the octet. This creates a larger negative charge in the creates a larger negative charge in the electron cloud than positive charge in electron cloud than positive charge in the nucleus, causing the electron the nucleus, causing the electron cloud to 'puff out' a little bit as an ion. cloud to 'puff out' a little bit as an ion. 

Ionic Radius vs. Atomic Ionic Radius vs. Atomic RadiusRadius

Ionization EnergyIonization Energy

Energy required to remove an Energy required to remove an electron from a gaseous atom (J)electron from a gaseous atom (J)

If an atom has a high ionization If an atom has a high ionization energy not likely to form a positive energy not likely to form a positive ionion

Tends to increase across a periodTends to increase across a period Tends to decrease down a groupTends to decrease down a group

11stst Ionization Energy Ionization Energy

ElectronegativityElectronegativity

Relative ability of an atom to attract Relative ability of an atom to attract electrons in a chemical bondelectrons in a chemical bond

Numerical value of 3.98 Paulings or Numerical value of 3.98 Paulings or lessless

Fluorine is the most electronegativeFluorine is the most electronegative atoms positioned closer to F have higher atoms positioned closer to F have higher

electronegativieselectronegativies Tends to increase across periodTends to increase across period Tends to decrease down a groupTends to decrease down a group

ElectronegativityElectronegativity

ReactivityReactivity

Reactivity refers to how likely orReactivity refers to how likely or

vigorously an atom is to react vigorously an atom is to react with other substances. with other substances.

This is usually determined by This is usually determined by two things:two things:

1) How easily electrons 1) How easily electrons can be removed can be removed

(ionization energy) from (ionization energy) from an atoman atom

2) or how badly an atom 2) or how badly an atom wants to take other wants to take other

atom's electrons atom's electrons (electronegativity)(electronegativity)

The transfer/interaction The transfer/interaction of electrons is the basis of of electrons is the basis of

chemical reactions.chemical reactions.

Period - reactivity decreases as you go from left to right across a period.

Group - reactivity increases as you go down a group

Why? The farther to the left and down the periodic chart you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity.

Reactivity of MetalsReactivity of Metals

Period - reactivity increases as you go from the left to the right across a period. Group - reactivity decreases as you go down the group.

Why? The farther right and up you go on the periodic table, the higher the electronegativity, resulting in a more vigorous exchange of electron.

Reactivity of Non-MetalsReactivity of Non-Metals

Electron AffinityElectron Affinity

Change in energy that occurs when a neutral Change in energy that occurs when a neutral atom acquires an electronatom acquires an electron Hopefully atom is become more stable by Hopefully atom is become more stable by

acquiring an elcectronacquiring an elcectron Measured with a negative valueMeasured with a negative value

The more negative the value the easier it is to The more negative the value the easier it is to acquire an electronacquire an electron

Tends to become more negative across a Tends to become more negative across a periodperiod

Tends to become more positive down a groupTends to become more positive down a group

Electron AffinityElectron Affinity

Summary of Periodic Summary of Periodic TrendsTrends