HYDROGEN : HYDROGEN
INTRODUCTION : INTRODUCTION In this lesson we will learn about the simplest atomic structure among all the elements with only one proton and one electron, forming more compounds than any other element, existing in nature as diatomic molecule (H2), with great industrial importance and a distinct place in chemical world:
HYDROGEN
Position of hydrogen in periodic table : Position of hydrogen in periodic table Electronic configuration is the basis for the placement of an element in periodic table at a specific place. Hydrogen shows resemblance with alkali metals (group Ist elements) as well as halogens (group 17th elements) in some respects but do not match completely with any of these.
This is the reason why position of hydrogen in periodic table is still a matter of discussion and remained undecided.
Resemblance Of Hydrogen With First group elements (Alkali Metals): : Resemblance Of Hydrogen With First group elements (Alkali Metals): Same valance shell electronic configuration of hydrogen and alkali metal shows that both have one electron in its valence shell.
H (Z=1): 1s1
Li (Z=3): 1s2, 2s1
Na (Z=11): 1s2, 2s22p6, 3s1
Both hydrogen an alkali metals are good reducing agents.
Like alkali metals hydrogen can also form halides which ionized in similar way in aqueous solution.
HCl (aq)?H+ (aq) + Cl-(aq)
NaCl(aq) ? Na+(aq) + Cl-(aq)
Like alkali metals hydrogen can also form compounds with non-metals. Such as Na2S and H2S.
Differences from Alkali Metals : Differences from Alkali Metals Hydrogen is a non-metal where as elements of first group are metals.
Alkali metals only form ionic compounds whereas hydrogen can form both covalent and ionic compounds
Hydrogen is a gas at room temperature but alkali metals are solids.
Unlike Na+ or K+ hydrogen ion (H+) is unstable in water and form hydronium ion by combining with water molecule. H+ + H2O ? H3O+
I.P. of hydrogen is very high as compared to alkali metals.I.P. of hydrogen is 313 Kcal mole-1.I.P. of alkali metals max. is 147 Kcal mole-1.
Resemblance Of Hydrogen With Halogens : Resemblance Of Hydrogen With Halogens Both Hydrogen and Halogens require one electron to complete their valence shell.
Both hydrogen and halogens are non-metals.
Both hydrogen and Halogens acts as negative ions when combined with metals.
Their molecules are diatomic.
Both halogens and hydrogen form ionic as well as covalent bond. NaH (Ionic), CH4 (Covalent) NaCl (Ionic), HCl (Covalent)
Like halogens hydrogen also form compound with both metals and non-metals. Hydrogen :H2S [S=non-metal], NaH [Na= metal] Halogens : HCl [H = non-metal], NaCl [Na=metal]
Differences from halogens : Differences from halogens Electronic configuration shows that in comparison to seven electrons in valence shell of halogens hydrogen has only one valence electron.
1H = 1S1
Halogens = nS2, nS5
Unlike halide (X-) ion, hydride (H-) ion is unstable in water.
H- + H2O ? H2 + OH-
UNIQUE ATOMIC STRUCTURE OF HYDROGEN : UNIQUE ATOMIC STRUCTURE OF HYDROGEN Hydrogen is the only element which has no neutron in its nucleus and by losing its single electron results in H+ (nucleus) with extremely small size ~ 1.5 X 10-3pm as compared to normal atomic and ionic size of 50-200 pm and hence H+ always found associated with other atoms or molecules and have no free existence.
Conclusion : Conclusion Above discussion results in unique behavior of hydrogen, therefore it is best placed separately in the periodic table.
Dihydrogen : Dihydrogen Most abundant (70% of total mass of universe) element in the universe.
Jupiter and Saturn consists of mostly hydrogen but due to its light nature, much less abundant in earth’s atmosphere (0.15% by mass)
Forms 15.4% of earths crust in combined form.
Isotopes of Hydrogen : Isotopes of Hydrogen Hydrogen has three isotopes
Protium
Deuterium
Tritium
Protium
Protium(1H1) is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton.
Slide 12 : Deuterium
Deuterium(1H2 or D): the other stable hydrogen isotope, contains one proton and one neutron in its nucleus.
Deuterium comprises 0.0026 – 0.0184% (by population, not by mass) of hydrogen samples on Earth. Deuterium is not radioactive, and does not represent a significant toxicity hazard.
Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water.
Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy.
Heavy water is used as a neutron moderator and coolant for nuclear reactors.
Deuterium is also a potential fuel for commercial nuclear fusion.
Tritium : Tritium Tritium(1H3 or T) contains one proton and two neutrons in its nucleus. .
It is radioactive, decaying into helium-3 through ß- decay with a half-life of 12.32 years.
Small amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases;
tritium has also been released during nuclear weapons tests.
It is used in thermonuclear fusion weapons, as a tracer in isotope geochemistry, and specialized in self-powered lighting devices.
Tritium was once routinely used in chemical and biological labelling experiments as a radiolabel (this has become less common).
D-T nuclear fusion uses tritium as its main reactant, along with deuterium, liberating energy through the loss of mass when the two nuclei collide and fuse under massive temperatures.