hydrogen occurs in combined state in which form on earth
Answers
Answer:
Hydrogen occurs in the earth's crust, atmosphere and in volcanic gases, also in the interior of the sun in the free state. In combined state it occurs in organic compounds, plants and animals, in acids and in water.
Explanation:
The name hydrogen comes from the Greek words "hydro" (meaning water) and "genes" (meaning creator). It was named by French chemist Antoine Lavoisier because when it burns it "creates water".
Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[7][note 1] Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.
Hydrogen, 1H
Hydrogen discharge tube.jpg
Purple glow in its plasma state
Hydrogen
Appearance
colorless gas
Standard atomic weight Ar, std(H)
[1.00784, 1.00811] conventional: 1.008
↓
Li
– ← hydrogen → helium
Atomic number (Z)
1
Group
1: H and alkali metals
Period
period 1
Block
s-block
Element category
Reactive nonmetal
Electron configuration
1s1
Electrons per shell
1
Physical properties
Phase at STP
gas
Melting point
(H2) 13.99 K (−259.16 °C, −434.49 °F)
Boiling point
(H2) 20.271 K (−252.879 °C, −423.182 °F)
Density (at STP)
0.08988 g/L
when liquid (at m.p.)
0.07 g/cm3 (solid: 0.0763 g/cm3)[1]
when liquid (at b.p.)
0.07099 g/cm3
Triple point
13.8033 K, 7.041 kPa
Critical point
32.938 K, 1.2858 MPa
Heat of fusion
(H2) 0.117 kJ/mol
Heat of vaporization
(H2) 0.904 kJ/mol
Molar heat capacity
(H2) 28.836 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 15 20
Atomic properties
Oxidation states
−1, +1 (an amphoteric oxide)
Electronegativity
Pauling scale: 2.20
Ionization energies
1st: 1312.0 kJ/mol
Covalent radius
31±5 pm
Van der Waals radius
120 pm
Color lines in a spectral range
Spectral lines of hydrogen
Other properties
Natural occurrence
primordial
Crystal structure
hexagonalHexagonal crystal structure for hydrogen
Speed of sound
1310 m/s (gas, 27 °C)
Thermal conductivity
0.1805 W/(m·K)
Magnetic ordering
diamagnetic[2]
Magnetic susceptibility
−3.98·10−6 cm3/mol (298 K)[3]
CAS Number
12385-13-6
1333-74-0 (H2)
History
Discovery
Henry Cavendish[4][5] (1766)
Named by
Antoine Lavoisier[6] (1783)
Main isotopes of hydrogen
Isotope Abundance Half-life (t1/2) Decay mode Product
1H 99.98% stable
2H 0.02% stable
3H trace 12.32 y β− 3He
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The universal emergence of atomic hydrogen first occurred during the recombination epoch (Big Bang). At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays a particularly important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) when it is known as a hydride, or as a positively charged (i.e., cation) species denoted by the symbol H+. The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the Schrödinger equation can be solved analytically,[8] study of the energetics and bonding of the hydrogen atom has played a key role in the development of quantum mechanics.
Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[9] and that it produces water when burned, the property for which it was later named: in Greek, hydrogen means "water-former".
Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water.[10] Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for the fertilizer market. Hydrogen is problematic in metallurgy because it can embrittle many metals,[11] complicating the design of pipelines and storage tanks.[12]