Download Hydrogen (/ˈhaɪdrɵdʒən/ HY-drə-jən)[7] is a chemical element

Hydrogen (/ˈhaɪdrɵdʒən/ HY-drə-jən)[7] is a chemical element with symbol H and
atomic number 1. With an average atomic weight of 1.00794 u (1.007825 u for hydrogen-1),
hydrogen is the lightest element and its monatomic form (H1) is the most abundant chemical
substance.
At standard temperature and pressure, hydrogen is a colourless, odorless, tasteless,
non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2.
Naturally occurring atomic hydrogen is rare on Earth because hydrogen readily forms
covalent compounds with most elements and is present in the water molecule and in most
organic compounds. Hydrogen plays a particularly important role in acid-base chemistry with
many reactions exchanging protons between soluble molecules.
In ionic compounds, it can take a negative charge (an anion known as a hydride and
written as H−), or as a positively charged species H+. The latter cation is written as though
composed of a bare proton, but in reality, hydrogen cations in ionic compounds always occur
as more complex species.
The most common isotope of hydrogen is protium (name rarely used, symbol 1H)
with a single proton and no neutrons. As the simplest atom known, the hydrogen atom has
been of theoretical use. For example, as the only neutral atom with an analytic solution to the
Schrödinger equation, the study of the energetics and bonding of the hydrogen atom played a
key role in the development of quantum mechanics.
Deuterium (symbol D or 2H, also known as heavy hydrogen) is one of two stable
isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in 6,420
of hydrogen (~156.25 ppm on an atom basis). Deuterium accounts for approximately 0.0156
percent (or on a mass basis: 0.0312 percent) of all the naturally occurring hydrogen in the
oceans, while the most common isotope (hydrogen-1 or protium) accounts for more than
99.98 percent. The abundance of deuterium changes slightly from one kind of natural water
to another.
The nucleus of deuterium, called a deuteron, contains one proton and one neutron,
whereas the far more common hydrogen isotope, protium, has no neutron in the nucleus. The
deuterium isotope's name is formed from the Greek deuteros meaning "second", to denote the
two particles composing the nucleus. Deuterium was discovered and named in 1931 by
Harold Urey, earning him a Nobel Prize in 1934. This followed the discovery of the neutron
in 1932, which made the nuclear structure of deuterium obvious. Soon after deuterium's
discovery, Urey and others produced samples of "heavy water" in which the deuterium has
been highly concentrated with respect to the protium.
Tritium (/ˈtrɪtiəm/ or /ˈtrɪʃiəm/; symbol T or 3H, also known as hydrogen-3) is a
radioactive isotope of hydrogen. The nucleus of tritium (sometimes called a triton) contains
one proton and two neutrons, whereas the nucleus of protium (by far the most abundant
hydrogen isotope) contains one proton and no neutrons. Naturally occurring tritium is
extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere
with cosmic rays. The name of this isotope is formed from the Greek word "tritos" meaning
"third".
Standard form of the periodic table. The colors represent different series of elements
explained below.
A periodic table is a tabular display of the chemical elements, organized on the basis
of their atomic numbers, electron configurations, and recurring chemical properties.
Elements are presented in increasing atomic number. The main body of the standard form
of table is an 18 × 7 grid, and elements with the same number of valence electrons are kept
together in groups, such as the halogens and the noble gases. There are four distinct
rectangular areas or blocks. The f-block is usually not included in the main table, but rather
is floated below, as an inline f-block would often make the table impractically wide. Using
periodic trends, the periodic table can help predict the properties of various elements and
the relations between properties. As a result it provides a useful framework for analyzing
chemical behavior, and is widely used in chemistry and other sciences.



t
e
Periodic table (standard form)
Group →
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18
↓ Period
1
1
2
He
H
3
2
4
LB
ie
5
B
3
1
112
M
Ng
a
13 14 15 16 17 18
Al Si P S Cl Ar
6
C
7 8
N O
9 10
F Ne
4
5
6
7
1
920
25
21 22 23 24
26 27 28 29 30 31 32 33 34 35 36
C
M
Sc Ti V Cr
Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Ka
n
3
7
42
38 39 40 41
43 44 45 46 47 48 49 50 51 52 53 54
M
RSr Y Zr Nb
Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
o
b
5
5
56
* 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
B
C
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
a
s
8
7
11
11
11
88
10 10 10 10 10 10 11 11 11
11
11
**
3
5
7
R
4 5 6 7 8 9 0 1 2
4
6
F
Uu
Uu
Uu
a
Rf Db Sg Bh Hs Mt Ds Rg Cn
Fl
Lv
r
t
p
s
* Lanthanides
** Actinides
69
57 58 59 60 61 62 63 64 65 66 67 68
70
T
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er
Yb
m
10
95 96
10
10
89 90 91 92 93 94
97 98 99
1
A C
0
2
Ac Th Pa U Np Pu
Bk Cf Es
M
m m
Fm
No
d
11
8
Uu
o
71
Lu
10
3
Lr
This is an 18-column periodic table layout, which has come to be referred to as the common or
standard form, on account of its popularity. It is also sometimes referred to as the long form, in
comparison to the short form or Mendeleev-style, which omits groups 3–12. The wide periodic table
incorporates the lanthanides and the actinides, rather than separating them from the main body of the
table. The extended periodic table adds the 8th and 9th periods, including the superactinides.
Some element categories in the periodic table
Metals
Nonmetals
Unkno
wn
Alkali Inner transition
Alka
Post- Metallo
Nob chemic
ne
metals
Transit
Other
li
transiti ids
Halog le al
earth
ion
nonmet
meta
on
ens
gase propert
metal Lanthani Actini metals
als
ls
metals
s
des
des
ies
s
Color of the atomic number shows state
of matter
Border
shows
(at standard conditions: 0 °C and 1 atm):
black=S green=Li red= grey=Unkn
olid
quid
Gas
own
natural
occurrence
:
Primordial
From
decay
Synthetic