newFLAT 30% off & $20 sign up bonus Order Now

newFLAT 30% off & $20 sign up bonus Order Now

Save Time and Improve Grade - Get Professional Help Now!
logo

Understanding Atomic Radius Trends: The 2 Key Principles

Home / Blog / Understanding Atomic Radius Trends: The 2 Key Principles

blog
 Admin  August 19, 2019  Homework  0

An atom is defined as one of the basic unit of any chemical element. Any chemical element from small to large weight has large atomic number has some definite atomic radius. The radius is defined as the distance between the centre of a circular substance to its outer perimeter. Hence, the atomic radius is the distance between the centre of nuclei and the electron in the outermost shell. The atomic radius are typically measured in very small SI unit of pico-meters, when 1 pm =  meters. The smallest average atomic radius of hydrogen (H) is about 25 pico-meters and caesium (Cs) has the largest average radius of about 260 pico-meters.

The Basics Of Atomic Radius Trend

There is an interesting trend about the atomic radius of elements in periodic table. The two main trends of atomic radius in the periodic table can be seen when the movement is from left to right i.e. moving within a period and other trend is when moving from top to bottom. The periodic table shown below gives the trend of increase of atomic radii in the direction of arrow. The very first atomic radius trend is that the size of atom decreases as we move from left to right through a period. Now, for each period of elements one new electron is being added to the very same shell. Now, at the time of addition of electron to an atom a proton is also added to the nucleus of the atom. The electrons are basically attracted to the nucleus and thus makes the radius of the atom small. For an example the atom of a carbon C has 6 atomic number of 6 electrons and 6 protons. Whereas, the fluorine atom contain 9 electrons and 9 protons. Hence, from the trend of atomic radius the atom of Carbon C has a larger radius than the radius of an atom of fluorine F as with the three extra protons of fluorine will attract the electrons with higher force than the Carbon atom and thus making the radius of Fluorine smaller than that of Carbon. This is indeed true as the atomic radius of the Carbon atom is about 70 pico-meters and the atomic radius of Fluorine is 50 pico-meters.

The second trend of atomic radius suggests that atomic radius increases as we move to the bottom of the periodic table from the top. As we move through each group the atom gets an additional orbit of electron and thus each orbit becomes further away from the nucleus of the atom and hence the atomic radius is increased. The valence band electrons that is the electrons in the outermost shell are not much attracted by the nucleus to make the atomic radius smaller due to the electron shielding effect. Electron shielding is basically an effect by which the inner shell electrons shields the electrons in the outer shell from electro-magnetic attraction of the positive charged nucleus to electrons. This attraction force is also reduced also when there are more electrons in one shell. Hence, due to electron shielding the electrons in valence band can’t get particularly close to the nucleus of the atom and as they can’t get any close thus the atom has a large radius. For example, the potassium (K) has a large radius than the sodium (Na) atom as the potassium atom has one extra orbit of electrons than the Na atom or the valence electrons are further away from the nucleus and hence the potassium has a large radius of an atom. The atomic radius of potassium atom is about 220 pm which is larger than the atomic radius of sodium which is 180 pm.

Empirical atomic radii:

The empirical atomic number table shows the element name, symbol and their corresponding atomic number and empirical atomic radius in pico-meters from which the two trends can be identified.

Atomic Number

Atomic Symbol

Name of Element

Empirical Atomic Radius (in pm)

1

H

Hydrogen

25

2

He

Helium

No data

3

Li

Lithium

145

4

Be

Beryllium

105

5

B

Boron

85

6

C

Carbon

70

7

N

Nitrogen

65

8

O

Oxygen

60

9

F

Fluorine

50

10

Ne

Neon

No data

11

Na

Sodium

180

12

Mg

Magnesium

150

13

Al

Aluminum

125

14

Si

Silicon

110

15

P

Phosphorus

100

16

S

Sulfur

100

17

Cl

Chlorine

100

18

Ar

Argon

No data

19

K

Potassium

220

20

Ca

Calcium

180

21

Sc

Scandium

160

22

Ti

Titanium

140

23

V

Vanadium

135

24

Cr

Chromium

140

25

Mn

Manganese

140

26

Fe

Iron

140

27

Co

Cobalt

135

28

Ni

Nickel

135

29

Cu

Copper

135

30

Zn

Zinc

135

31

Ga

Gallium

130

32

Ge

Germanium

125

33

As

Arsenic

115

34

Se

Selenium

115

35

Br

Bromine

115

36

Kr

Krypton

No data

37

Rb

Rubidium

235

38

Sr

Strontium

200

39

Y

Yttrium

180

40

Zr

Zirconium

155

41

Nb

Niobium

145

42

Mo

Molybdenum

145

43

Tc

Technetium

135

44

Ru

Ruthenium

130

45

Rh

Rhodium

135

46

Pd

Palladium

140

47

Ag

Silver

160

48

Cd

Cadmium

155

49

In

Indium

155

50

Sn

Tin

145

51

Sb

Antimony

145

52

Te

Tellurium

140

53

I

Iodine

140

54

Xe

Xenon

No data

55

Cs

Caesium

260

56

Ba

Barium

215

57

La

Lanthanum

195

58

Ce

Cerium

185

59

Pr

Praseodymium

185

60

Nd

Neodymium

185

61

Pm

Promethium

185

62

Sm

Samarium

185

63

Eu

Europium

185

64

Gd

Gadolinium

180

65

Tb

Terbium

175

66

Dy

Dysprosium

175

67

Ho

Holmium

175

68

Er

Erbium

175

69

Tm

Thulium

175

70

Yb

Ytterbium

175

71

Lu

Lutetium

175

72

Hf

Hafnium

155

73

Ta

Tantalum

145

74

W

Tungsten

135

75

Re

Rhenium

135

76

Os

Osmium

130

77

Ir

Iridium

135

78

Pt

Platinum

135

79

Au

Gold

135

80

Hg

Mercury

150

81

Tl

Thallium

190

82

Pb

Lead

180

83

Bi

Bismuth

160

84

Po

Polonium

190

85

At

Astatine

No data

86

Rn

Radon

No data

87

Fr

Francium

No data

88

Ra

Radium

215

89

Ac

Actinium

195

90

Th

Thorium

180

91

Pa

Protactinium

180

92

U

Uranium

175

93

Np

Neptunium

175

94

Pu

Plutonium

175

95

Am

Americium

175

96

Cm

Curium

No data

97

Bk

Berkelium

No data

98

Cf

Californium

No data

99

Es

Einsteinium

No data

100

Fm

Fermium

No data

101

Md

Mendelevium

No data

102

No

Nobelium

No data

103

Lr

Lawrencium

No data

104

Rf

Rutherfordium

No data

105

Db

Dubnium

No data

106

Sg

Seaborgium

No data

107

Bh

Bohrium

No data

108

Hs

Hassium

No data

109

Mt

Meitnerium

No data

110

Ds

Darmstadtium

No data

111

Rg

Roentgenium

No data

112

Cn

Copernicium

No data

113

Nh

Nihonium

No data

114

Fl

Flerovium

No data

115

Mc

Moscovium

No data

116

Lv

Livermorium

No data

117

Ts

Tennessine

No data

118

Og

Oganesson

No data

 

Atomic Radius Trend Exceptions

By observation of the above table it can be seen that in some cases, specifically in three cases. The first case is the exception for noble gases which are helium, neon, argon, krypton, xenon and radon. This exception occurs because the bonding of the noble gases are different from the bonding of other atoms. As the atomic radius is the half of the distance between the two atoms and hence the difference in distance between the atoms affects the length of atomic radius. In case of noble gases the outermost orbit is completely filled and hence there exist no covalent force between the atoms of noble gases as electrons are not shared by the atoms. The noble gas atoms are kept together by Van-der Waals force which is weaker than the covalent force. Thus the gapping between the two nuclei is larger for noble gases compared to the gapping between other atoms. Hence, if the empirical radius is calculated for noble gases then it will be overestimated. Hence, any of the noble gases has the empirical radius and thus don’t follow the trend of atomic radius. It can be also be seen that the lanthanide and actinide series does not follows the two trends like they don’t follow many other periodic table trends.

Significance Of The Trend Information

This atomic radius trends can be used to estimate the reaction properties between elements while forming a compound as the atoms with smaller atomic radii are more reactive than the larger ones. This is why the halogens in group 17 are more reactive than other group elements. Also, among the halogens fluorine has the lowest atomic radii and thus it is the most reactive element.

Top Periodic Trends In Atomic Radius

Thus the two atomic radius trends, in brief, are i) reduction of atomic radii as we move downwards in a group ii) The second trend of atomic radii is that the atomic radii decrease by moving left to right through a particular period. The few exceptions that exist in the periodic table for the radius trends are for halogens, lanthanides and actinides are explained for unusual atomic characteristics.

So, that was all about atomic radius trends. Didn’t the concept seem easy? Well, that’s not always the case. Students often find themselves struggling when it comes to other, more complex Chemistry concepts. Especially when students are supposed to make assignments on the same, the task gets a bit too tough. So, what to do in such a situation?

Tophomeworkhelper.com: Your ultimate Chemistry Homework Savior

Yes! You read that right. Just when you find yourself caught amid a pile of complex homework tasks, be it Maths or Chemistry Homework help, tophomeworkhelper.com is the one-stop solution to opt for. This amazing service is backed up by professionals having Masters and PhDs in respective subjects and also possesses years of experience in homework writing. So, these unmatched writers not only know what resources to refer but are also aware of all the tips and tricks that would make your assignments outstanding. All you have to do is reach out to tophomeworkhelper.com, share your concern and relax. Rest assured, that you’ll be heading towards a better learning and bright academic career and that too, without missing out on any of those stringent deadlines!


Do you want to share?

Comments 0


LEAVE A REPLY

Place order

Complete and submit the form to get $20

Recent Post

Active Vs Passive Immunity

 Admin  September 4, 2019

Categories

Popular Posts

Subscribe Newsletter

You can place your order for free now. Simply submit your order and see what our writers can Subscribe to get regular update!