Which group has high atomic size?
Answers
Answer:
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Answer:
As can be seen in the figures below, the atomic radius increases from top to bottom in a group, and decreases from left to right across a period. Thus, helium is the smallest element, and francium is the largest.
Explanation:
Periodic Trends — Atomic and Ionic Radii
1A 2A 3A 4A 5A 6A 7A 8A
(1) (2) (13) (14) (15) (16) (17) (18)
3B 4B 5B 6B 7B — 8B — 1B 2B
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
1
H
78
He
32
2
Li
152
Be
113
B
83
C
77
N
71
O
73
F
71
Ne
70
3
Na
186
Mg
160
Al
143
Si
117
P
115
S
104
Cl
99
Ar
98
4
K
227
Ca
197
Sc
161
Ti
145
V
132
Cr
125
Mn
124
Fe
124
Co
125
Ni
125
Cu
128
Zn
133
Ga
122
Ge
123
As
125
Se
117
Br
114
Kr
112
5
Rb
248
Sr
215
Y
181
Zr
160
Nb
143
Mo
136
Tc
136
Ru
134
Rh
134
Pd
138
Ag
144
Cd
149
In
163
Sn
141
Sb
141
Te
143
I
133
Xe
130
6
Cs
265
Ba
217
La
188
Hf
156
Ta
143
W
137
Re
137
Os
135
Ir
136
Pt
138
Au
144
Hg
160
Tl
170
Pb
175
Bi
155
Po
167
At
n.a.
Rn
145
7
Fr
270
Ra
223
Ac
188
Rf
150
Db
139
Sg
132
Bh
128
Hs
126
Mt
n.a.
Ds
n.a.
Rg
n.a.
Uub
n.a.
—
Uuq
n.a.
—
—
—
—
6
Ce
182
Pr
183
Nd
182
Pm
181
Sm
180
Eu
185
Gd
180
Tb
178
Dy
177
Ho
177
Er
176
Tm
175
Yb
170
Lu
173
7
Th
180
Pa
161
U
154
Np
150
Pu
175
Am
173
Cm
174
Bk
170
Cf
169
Es
203
Fm
n.a.
Md
n.a.
No
n.a.
Lr
n.a.
Atomic radii reported in units of picometers (pm).
Data taken from John Emsley, The Elements, 3rd edition. Oxford: Clarendon Press, 1998.
The atomic radius is the distance from the nucleus of an atom to the outermost electrons. Since the orbitals around an atom are defined in terms of a probability distribution in quantum mechanics, and do not have fixed boundaries, determining where an atom "stops" is not very straightforward. By comparing the bond lengths of a number of representative compounds of an element, an average size for most atoms can be determined.
The atomic radius can also be defined in other ways. The van der Waals radius (also known as the nonbonding atomic radius) is the radius of an atom which is not bonded to other atoms; this is determined by measuring the distance between atomic nuclei which are in direct but nonbonding contact with each other in a crystal lattice. The covalent atomic radius (also known as the bonding atomic radius) is determined for metals by taking one-half of the distance between two adjacent atoms in a metallic crystal, or one-half the distance between like bonded atoms for nonmetals.
Unfortunately, it is not possible to determine the radius for every element on the periodic table in the same way, and consequently, it is sometimes difficult to make comparisons between different sets of data. In the table above, most of the atomic radii listed are average atomic radii, while for the halogens (Group 7A) and the noble gases (Group 8A) the covalent radius is used.
Atomic radii vary in a predictable way across the periodic table. As can be seen in the figures below, the atomic radius increases from top to bottom in a group, and decreases from left to right across a period. Thus, helium is the smallest element, and francium is the largest.
From top to bottom in a group, orbitals corresponding to higher values of the principal quantum number (n) are being added, which are on average further away from the nucleus, thus causing the size of the atom to increase.
From left to right across a period, more protons are being added to the nucleus, but the electrons which are being added are being added to the valence shell, not to the lower energy levels. As more protons are added to the nucleus, the electrons in the valence shell feel a higher effective nuclear charge — the sum of the charges on the protons in the nucleus and the charges on the inner, core electrons. (See figure below.) The valence electrons are therefore held more tightly, and the size of the atom contracts across a period.
The following charts illustrate the general trends in the radii of atoms:
The sizes of cations and anions follow similar trends to those of neutral atoms. In general, anions are larger than the corresponding neutral atom, since adding electrons increases the number of electron-electron repulsion interactions that take place. Cations are smaller than the corresponding neutral atoms, since the valence electrons, which are furthest away from the nucleus, are lost. Taking more electrons away from the cation further reduces the radius of the ion.
The table below illustrates these trends for the main group elements. For elements which form more than one cation, the cation charges and sizes are listed in two separate columns. The transition metals and inner transition metals have been omitted, since almost all of those elements can form two or more possible cations.