Atomic Radius of Chemical Elements

Periodic Table of Elements - atomic radius
1
H

Hydrogen

31 pm

2
He

Helium

28 pm

3
Li

Lithium

121 pm

4
Be

Beryllium

96 pm

5
B

Boron

84 pm

6
C

Carbon

69 pm

7
N

Nitrogen

71 pm

8
O

Oxygen

66 pm

9
F

Fluorine

64 pm

10
Ne

Neon

58 pm

11
Na

Sodium

166 pm

12
Mg

Magnesium

141 pm

13
Al

Aluminium

121 pm

14
Si

Silicon

111 pm

15
P

Phosphorus

107 pm

16
S

Sulfur

105 pm

17
Cl

Chlorine

102 pm

18
Ar

Argon

106 pm

19
K

Potassium

203 pm

20
Ca

Calcium

176 pm

21
Sc

Scandium

170 pm

22
Ti

Titanium

160 pm

23
V

Vanadium

153 pm

24
Cr

Chromium

139 pm

25
Mn

Manganese

139 pm

26
Fe

Iron

132 pm

27
Co

Cobalt

126 pm

28
Ni

Nickel

124 pm

29
Cu

Copper

132 pm

30
Zn

Zinc

122 pm

31
Ga

Gallium

122 pm

32
Ge

Germanium

122 pm

33
As

Arsenic

119 pm

34
Se

Selenium

120 pm

35
Br

Bromine

120 pm

36
Kr

Krypton

116 pm

37
Rb

Rubidium

220 pm

38
Sr

Strontium

195 pm

39
Y

Yttrium

190 pm

40
Zr

Zirconium

175 pm

41
Nb

Niobium

164 pm

42
Mo

Molybdenum

154 pm

43
Tc

Technetium

147 pm

44
Ru

Ruthenium

146 pm

45
Rh

Rhodium

142 pm

46
Pd

Palladium

139 pm

47
Ag

Silver

144 pm

48
Cd

Cadmium

144 pm

49
In

Indium

142 pm

50
Sn

Tin

139 pm

51
Sb

Antimony

139 pm

52
Te

Tellurium

138 pm

53
I

Iodine

139 pm

54
Xe

Xenon

140 pm

55
Cs

Caesium

244 pm

56
Ba

Barium

215 pm

57-71

 

Lanthanoids

 

72
Hf

Hafnium

175 pm

73
Ta

Tantalum

170 pm

74
W

Tungsten

162 pm

75
Re

Rhenium

151 pm

76
Os

Osmium

144 pm

77
Ir

Iridium

141 pm

78
Pt

Platinum

136 pm

79
Au

Gold

136 pm

80
Hg

Mercury

132 pm

81
Tl

Thallium

145 pm

82
Pb

Lead

146 pm

83
Bi

Bismuth

148 pm

84
Po

Polonium

140 pm

85
At

Astatine

150 pm

86
Rn

Radon

150 pm

87
Fr

Francium

260 pm

88
Ra

Radium

221 pm

89-103

 

Actinoids

 

104
Rf

Rutherfordium

157 pm

105
Db

Dubnium

149 pm

106
Sg

Seaborgium

143 pm

107
Bh

Bohrium

141 pm

108
Hs

Hassium

134 pm

109
Mt

Meitnerium

129 pm

110
Ds

Darmstadtium

128 pm

111
Rg

Roentgenium

121 pm

112
Cn

Copernicium

122 pm

113
Nh

Nihonium

175 pm

114
Fl

Flerovium

175 pm

115
Mc

Moscovium

157 pm

116
Lv

Livermorium

164 pm

117
Ts

Tennessine

 

118
Og

Oganesson

 

57
La

Lanthanum

207 pm

58
Ce

Cerium

204 pm

59
Pr

Praseodymium

203 pm

60
Nd

Neodymium

201 pm

61
Pm

Promethium

199 pm

62
Sm

Samarium

198 pm

63
Eu

Europium

198 pm

64
Gd

Gadolinium

196 pm

65
Tb

Terbium

194 pm

66
Dy

Dysprosium

178 pm

67
Ho

Holmium

192 pm

68
Er

Erbium

189 pm

69
Tm

Thulium

190 pm

70
Yb

Ytterbium

187 pm

71
Lu

Lutetium

187 pm

89
Ac

Actinium

215 pm

90
Th

Thorium

206 pm

91
Pa

Protactinium

161 pm

92
U

Uranium

196 pm

93
Np

Neptunium

190 pm

94
Pu

Plutonium

187 pm

95
Am

Americium

180 pm

96
Cm

Curium

169 pm

97
Bk

Berkelium

170 pm

98
Cf

Californium

 

99
Es

Einsteinium

 

100
Fm

Fermium

 

101
Md

Mendelevium

 

102
No

Nobelium

 

103
Lr

Lawrencium

 

Atomic Radius of Chemical Elements

Atomic Radius of Chemical Elements

It must be noted, atoms lack a well-defined outer boundary. The atomic radius of a chemical element is a measure of the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Therefore, there are various non-equivalent definitions of atomic radius.

  • Van der Waals radius. In principle, Vana der Waals radius is half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule.
  • Ionic radius. An ionic radius is one-half the distance between the nuclei of two ions in an ionic bond.
  • Covalent radius. Covalent radius is the nominal radius of the atoms of an element when covalently bound to other atoms.
  • Metallic radius. A metallic radius is one-half the distance between the nuclei of two adjacent atoms in a crystalline structure, when joined to other atoms by metallic bonds.

On the periodic table of the elements, atomic radius tends to increase when moving down columns, but decrease when moving across rows (left to right). Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm. The atomic radii decrease across the periodic table because as the atomic number increases, the number of protons increases across the period, but the extra electrons are only added to the same quantum shell. Therefore, the effective nuclear charge towards the outermost electrons increases, drawing the outermost electrons closer. As a result, the electron cloud contracts and the atomic radius decreases.

atomic radius - periodic tableThe volume of an atom is about 15 orders of magnitude larger than the volume of a nucleus. For uranium atom, the Van der Waals radius is about 186 pm = 1.86 ×10−10m. The Van der Waals radius, rw, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. Assuming spherical shape, the uranium atom have volume of about 26.9 ×10−30 m3. But this “huge” space is occupied primarily by electrons, because the nucleus occupies only about 1721×10−45 m3 of space. These electrons together weigh only a fraction (let say 0.05%) of entire atom.

It may seem, that the space and in fact the matter is empty, but it is not. Due to the quantum nature of electrons, the electrons are not point particles, they are smeared out over the whole atom. The classical description cannot be used to describe things on the atomic scale. On the atomic scale, physicists have found that quantum mechanics describes things very well on that scale. Particle locations in quantum mechanics are not at an exact position, they are described by a probability density function. Therefore the space in an atom (between electrons and an atomic nucleus) is not empty, but it is filled by a probability density function of electrons (usually known as “electron cloud“).

Density of Chemical Elements

Typical densities of various substances are at atmospheric pressure.

Density is defined as the mass per unit volume. It is an intensive property, which is mathematically defined as mass divided by volume:

ρ = m/V

In words, the density (ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance. The standard SI unit is kilograms per cubic meter (kg/m3). The Standard English unit is pounds mass per cubic foot (lbm/ft3).

Density and Atomic Radii

Since the density (ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance, it is obvious, the density of a substance strongly depends on its atomic mass and also on the atomic number density (N; atoms/cm3),

  • Atomic Weight. The atomic mass is carried by the atomic nucleus, which occupies only about 10-12 of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Therefore it is determined by the mass number (number of protons and neutrons).
  • Atomic Number Density. The atomic number density (N; atoms/cm3), which is associated with atomic radii, is the number of atoms of a given type per unit volume (V; cm3) of the material. The atomic number density (N; atoms/cm3) of a pure material having atomic or molecular weight (M; grams/mol) and the material density (⍴; gram/cm3) is easily computed from the following equation using Avogadro’s number (NA = 6.022×1023 atoms or molecules per mole): Atomic-Number-Density

Since nucleons (protons and neutrons) make up most of the mass of ordinary atoms, the density of normal matter tends to be limited by how closely we can pack these nucleons and depends on the internal atomic structure of a substance. The densest material found on earth is the metal osmium, but its density pales by comparison to the densities of exotic astronomical objects such as white dwarf stars and neutron stars.

If we include man made elements, the densest so far is Hassium. Hassium is a chemical element with symbol Hs and atomic number 108. It is a synthetic element (first synthesised at Hasse in Germany) and radioactive. The most stable known isotope, 269Hs, has a half-life of approximately 9.7 seconds. It has an estimated density of 40.7 x 103 kg/m3. The density of Hassium results from its high atomic weight and from the significant decrease in ionic radii of the elements in the lanthanide series, known as lanthanide and actinide contraction.

Properties of other elements