Mendeleev’s Periodic Table Mendeleev’s arrange them known 63 elements in order of their increasing atomic mass and observed regularity in properties of elements . Among chemical properties mainly considered Oxides & Hydrides Mendeleev’s Periodic Lawo “Physical & Chemical properties of elements are periodic function of their atomic masses’’ Achievements More systematic and easy approached . Correction of atomic mass of few elements on the basis of position of elements in periodic table Mendeleev corrected atomic masses of few elements.
Production of few elementsPredicted eka-Boron eka-Aluminium eks-siliconLater Scandium Gallium GermaniumDiscovered Limitationso Position of hydrogen was not justified as it represents to both alkali metals (1st group) (Li, Na, K….etc) & halogens (Cl , Br, F).o Position of Isotopes could not be justified as these are the atoms of same elements having same atomic no. but different atomic mass.o Some of the elements with dissimilar properties where put together.Eg:- Coinage metal like Cu,Ag & Au where arreanged with alkali metals .
o Mendeleev could be explain the cause of periodicity.o Nine elements in 8th group where arranged in the form of three trends without any justificationo Their was no separate place for Lanthanides & Actinides Modern Periodic table In 1913 “ Henry Moseley” showed that atomic no. is more fundamental properties then atomic weight accordingly to introduce. Modern Periodic Law “Physical & Chemical properties are the periodic function of their no.” . Elements when arranged in order of increasing atomic no. led to the classification called modern periodic table. Total 18th vertical column ------ GROUP 7 Horizontal rows ------------Periods
PeriodicityReaccurence of elements with similar propertiesAt regular interval when arranged in order of increasingAtomic no. is called periodicity. Cause of periodicitySimilar electronic configuration in outermost shell at definite interval.
Atomic Radius Generally it is defined as the distance of seperation b/w centre of nucleus and outer most shell of electron in an isolated atom. Difficulties In Measuring Atomic Radiuso According to probability picture of an atom there is no definite boundary of atom.o It is not possible to isolate an atom.o Atomic radius of an atom varies from one bounded state to another. Eg.:- Cl in Nacl & In Cl2. Co-valent Radius• It is defined as half of the distance of separation b/w nuclei of two covalently bonded similar atom by a single covalent bond.
Vander Wal’s Radius Half of the inter nuclear distance b/w adjacent atom (non- bonded) in a compound in solid state.
It is also known as inert gas radii because radius of nobel gases is always measured in term of RvwBecause they are generally not involved in bond formation.(except Xe , Kr). Metallic Radius Half of the inter nuclear distance separating metal cores in a metallic crystals. General trendso Across period L to R ( Atomic radius decreases due to increases in effective nuclear charge which tends to pull electron cloud closer.
o Down the group atomic radius increases dueTo increases in no. of shells and decreases in effectiveNuclear charge. Shielding EffectsThe inner electron screen the outer electron from nuclear attraction. Ionic Radius It is defined as the distance from centre of nucleus up to which it interfaces the ionic bond (e- cloud). Cation Cation is always smaller than parent atom ( due to decreases in no. of electron nuclear attraction per electron increases)
Anion Anion is greater than parent atom ( due to increases in no. of electron per e- nuclear attraction decreases and hence e- cloud moves furthers. Ionization Enthalpy / Energy The amount of energy required to remove an electron from outer most shell of isolated gases atom . So as to convert it into gases +ve ions. Endothermic always +ve Factors effecting Ionization Enthalpyo Ionization Enthalpy is directly proportional to Nuclear chargeo Ionization Enthalpy is inversely proportional to sizeo Ionization Enthalpy is inversely proportional to shielding effect.
o Electronic Arrangemento Half field and fully field orbital shows extra stability and hence have higher Ionization Energy. Successive Ionization EnergyIonization Energy is always higher ( energy required to remove subsequent electron. Mg--Mg+Mg2+ IE1 IE2 Electron gain Enthalpy The amount of energy released when an extra electron is added to isolated neutral gases atom . So as to convert it in to gases –ve ions . Depending upon the process is exo or endothermic . O+e- O- + e- ( released energy) (provide energy)
Higher the magnitude of electron gain Enthalpy more is the tendency of an atom to gain an e- and besides this it is also important to retain an e- . The highest –ve values are Halogens . Factors Effecting of Electron gain Enthalpy Electron gain Enthalpy is inversely proportional to atomic sizes . Electron gain Enthalpy is directly proportional to Nuclear charge. Electronic Arrangement Atoms of element having half field & fully field orbital have very low magnitude of Electron gain Enthalpy. Successive Electron gain Enthalpy O + e- O- (-ve) ( exothermic) O- + e- O2-(+ve) (endothermic)Repulsion overcome + energy is required
Electro negativityThe tendency of an atom to attract shared paired ofelectron towards itself is called electro negativity.