periodic table and atomic structure
TRANSCRIPT
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