Periodic table and atomic structure

PERIODIC TABLE AND ATOMIC STRUCTURE

Periodic Table

• systematic classification of elements based on properties of the elements

Early Classification Dobereiner Mendeleev

metalsLusterMalleableDuctileGood conductorsOf electricity and heat

Non metals

DullBrittleGood insulators of Heat and electricity

Triads- common properties

E.g, Cl Br IAll non metals

React with water To form acids whoseFormulas are similar

Columns : called families

Have similar properties

Periods or SeriesShow periodicity of Properties which Means repetition ofProperties after a Regular interval

IA

IIA

IIIA

IB

IIB

VIIIA

IVA

VA

VIA

VIIA

Na Mg Al Si P S Cl

K

Na H2O NaOH H2+ +

Na- solid, reacts violently with water to form a strong base

Mg O2 MgO

MgO H2O Mg( OH) 2

+

+

Mg- solid, reacts less readily with water to form a weak base

Al, Si, P, S- properties of these elements will continue to change at a regular sequence

Cl- gas instead of a solid, reacts with water to form an acid instead of a base

Solid, reacts with water to form strong base

Na- solid, reacts violently with water to form a strong base

Na H2O NaOH H2+ +

Mg- solid, reacts less readily with water to form a weak base

Mg O2 MgO

MgO H2O Mg( OH) 2

+

+

• Al, Si, P, S- properties of these elements will continue to change at a regular sequence

• Cl- gas instead of a solid, reacts with water to form an acid instead of a base

• Mendeleev’s Periodic Law- When elements are arranged in the order that closely approximates their atomic masses, they exhibit periodicity of properties

IA

IIA

IIIA

VIIIA

IVA

VA

VIA

VIIA

Na Mg Al Si P S Cl

K

22.9 24.3

Te I127.6 126.9

26.9

• Modern Periodic Law- When elements are arranged in the order of increasing atomic number, they exhibit periodicity of properties after a regular interval .(

• sp pattern of electron distribution- law of octaves)• Moseley – physicist who established that atomic

number was the correct basis for arranging the elements that will then show periodicity of properties.

IA

IIA

IIIA

VIIIA

IVA

VA

VIA

VIIA

Na Mg Al Si P S Cl

K

22.9 24.3

Te I127.6 128.9

26.9

11 12

19

52 53

13 14 15 16 17

H1

s s p s p s d p s d p s f d p s f d p

periodicity of properties

GENERALIZATIONS OF THE PERIODIC TABLE

• For both A and B Families• Period Number= gives the number of the

outermost energy level ( called valence shell)

• For A Families only• Group Number= gives the number of valence

electrons

• For B Families only• Group Number= gives the number of valence

electrons and electrons found in the orbital filling with them

• Elements of Group VIIIA are chemically stable• Ns2np6 configuration = Octet Rule : all

electrons in the valence shell are paired with opposite spin

• • Ns2 Rule of 2 = electrons are also pair and of

opposite spin

• Elements can attain stability , either by

– Losing electrons– Gaining electrons– Sharing electrons ( gaining & gaining of e’s)

• thru the use of low energy to attain the stability

IA 1 valence e’ 1 e’ lost + 1 ion cation

cation

cationII A 2 valence e’ 2 e’ lost +2 ion

IIIA 3 valence e’ +3 ion3 e’ lost

VA 5 valence e’ 3 e’ gain -3 ionanion

VI A 6 valence e’ 2 e’ gain anion-2 ion

VII A 7 valence e’ 1 e’ gain -1 ion anion

IV A 4 valence e’Share their e’s

ElectropositiveAnd orelectronegative

TRENDS IN THE PERIODIC PROPERTIES

Periodic Properties

Atomic sizeIonization

Energy

Electron Affinity

Metallic Property

Non metallic Property

electronegativity

• Trends in properties mean– Elements of the periodic table show different

Periodic properties . These in turn can be predicted from the relative positions of the elements in the periodic table. Relative positions are designated by their periods and groups.

Property Period : Left to Right Group : Top to Bottom

Atomic Size decreases increases

Ionization Energy increases decreases

Electron Affinity increases decreases

Metallic Property decreases increases

Non metallic property increases decreases

electronegativity increases decreases

Valence e’ areMore drawn tonucleus

Valence e’ areLess drawn tonucleus

• Ionization energy- amount of energy needed (ENDOTHERMIC c ) to allow the lost of an outermost electron which is equal

• to the amount of energy to be released ( EXOTHERMIC) when the electron is gained back ( electron affinity)

• IE = EA

• Metallic property= property which describes the tendency of an atom to lose its electrons

•

• Electrons loosely held; easily lost• electrons tightly held; easily gained not

easily lost

• Non metallic property= property which describes the tendency of an atom to hold its electrons and or to gain other electrons of other atoms.

Electronegativity = property which describes the tendency of an atom to attract electrons to itself in a

compound

H Cl

2.1 3.0