Editing Nonmetal (section)

====First row anomaly====
<div style="line-height:1px;">[[Image:1x1.png|link=|alt=A table with seven rows and ten columns. Rows are labeled on the left with a period number from 1 through 7. Columns are labeled on the bottom with a group number. Most cells represent a single chemical element and have two lines of information: the element's symbol on the top and its atomic number on the bottom. The table as a whole is divided into four rectangular areas separated from each other by narrow gaps. The first rectangle fills all seven rows of the first two columns. The rectangle is labeled "s-block" at the top and its two columns are labeled with group numbers "(1)" and "(2)" on the bottom. The cells in the first row - hydrogen and helium, with symbols H and He and atomic numbers 1 and 2 respectively - are both shaded red. The second rectangle fills the bottom two rows (periods 6 and 7) of the third column. Just above these cells is the label "f-block"; there is no group label on the bottom. The topmost cell - labeled "La-Yb" for elements 57-70 - is shaded green. The third rectangle fills the bottom four rows (periods 4 through 7) of the fourth column. Just above these cells is the label "d-block"; at the bottom is the label "(3-12)" for the group numbers of these elements. The topmost cell - labeled "Sc-Zn" for elements 21-30 - is shaded blue. The fourth and last rectangle fills the bottom six rows (periods 2 through 7) of the last six columns. Just above these cells is the label "p-block"; at the bottom are labels "(13)" through "(18) for the group numbers of these elements. The cells in the topmost row - for the elements boron (B,5), carbon (C,6), nitrogen (N,7), oxygen (O,8), fluorine (Fl,9), and neon (Ne,10) - are shaded yellow. Bold lines encircle the cells of the nonmetals - the top two cells on the left and 21 cells in the upper right of the table.]]</div>
{| class=" floatright" style="border-collapse:collapse; text-align:center;font-size:80%;line-height:1.1;margin-top:1.2em;"
| colspan=14 style="padding-bottom:3px;border:none;text-align:center;font-size:105%" | '''Condensed periodic table highlighting<br>the first row of each block: {{color box|{{element color|s-block}}|s}} {{color box|{{element color|p-block}}|p}} {{color box|{{element color|d-block}}|d}} and {{color box|{{element color|f-block}}|f}}'''
|-
| colspan=1 | '''Period'''
| colspan=2 | '''{{nowrap|s-block}}'''
| rowspan=9 style="padding:1px;" |
| colspan=1 |
| rowspan=9 style="padding:1px;" |
| colspan=1 |
| rowspan=9 style="padding:1px;" |
| colspan=6 |
|-
| '''1'''
| style="border:solid black;border-width:2px 1px 2px 2px;background-color:{{element color|s-block}};" | H <br>1
| style="border:solid black;border-width:2px 2px 2px 1px;background-color:{{element color|s-block}};" | He<br>2
| 
| 
| colspan=6 | <br>'''p-block'''
|-
| '''2'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Li<br>3
| style="border:solid black;border-width:1px 1px 1px 1px;" | Be<br>4
|
|
| style="border:solid black;border-width:2px 1px 2px 2px;background-color:{{element color|p-block}};" | B <br>5
| style="border:solid black;border-width:2px 1px 1px 1px;background-color:{{element color|p-block}};" | C <br>6
| style="border:solid black;border-width:2px 1px 1px 1px;background-color:{{element color|p-block}};" | N <br>7
| style="border:solid black;border-width:2px 1px 1px 1px;background-color:{{element color|p-block}};" | O <br>8
| style="border:solid black;border-width:2px 1px 1px 1px;background-color:{{element color|p-block}};" | F <br>9
| style="border:solid black;border-width:2px 2px 1px 1px;background-color:{{element color|p-block}};" | Ne<br>10
|-
| '''3'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Na<br>11
| style="border:solid black;border-width:1px 1px 1px 1px;" | Mg<br>12
|
| <br>'''{{nowrap|d-block}}'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Al<br>13
| style="border:solid black;border-width:1px 1px 1px 2px;" | Si<br>14
| style="border:solid black;border-width:1px 1px 1px 1px;" | P <br>15
| style="border:solid black;border-width:1px 1px 1px 1px;" | S <br>16
| style="border:solid black;border-width:1px 1px 1px 1px;" | Cl<br>17
| style="border:solid black;border-width:1px 2px 1px 1px;" | Ar<br>18
|-
| '''4'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | K <br>19
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ca<br>20
|
| style="border:solid black;border-width:1px 1px 1px 1px;background-color:{{element color|d-block}};" | Sc-Zn<br>21-30
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ga<br>31
| style="border:solid black;border-width:1px 1px 2px 2px;" | Ge<br>32
| style="border:solid black;border-width:1px 1px 1px 1px;" | As<br>33
| style="border:solid black;border-width:1px 1px 1px 1px;" | Se<br>34
| style="border:solid black;border-width:1px 1px 1px 1px;" | Br<br>35
| style="border:solid black;border-width:1px 2px 1px 1px;" | Kr<br>36
|-
| '''5'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Rb<br>37
| style="border:solid black;border-width:1px 1px 1px 1px;" | Sr<br>38
| <br>'''{{nowrap|f-block}}'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Y-Cd<br>39-48
| style="border:solid black;border-width:1px 1px 1px 1px;" | In<br>49
| style="border:solid black;border-width:1px 1px 1px 1px;" | Sn<br>50
| style="border:solid black;border-width:1px 1px 2px 2px;" | Sb<br>51
| style="border:solid black;border-width:1px 1px 2px 1px;" | Te<br>52
| style="border:solid black;border-width:1px 1px 2px 1px;" | I <br>53
| style="border:solid black;border-width:1px 2px 1px 1px;" | Xe<br>54
|-
| '''6'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Cs<br>55
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ba<br>56
| style="border:solid black;border-width:1px 1px 1px 1px;background-color:{{element color|f-block}};" | La-Yb<br>57-70
| style="border:solid black;border-width:1px 1px 1px 1px;" | ''Lu-Hg<br>71-80''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Tl<br>81
| style="border:solid black;border-width:1px 1px 1px 1px;" | Pb<br>82
| style="border:solid black;border-width:1px 1px 1px 1px;" | Bi<br>83
| style="border:solid black;border-width:1px 1px 1px 1px;" | Po<br>84
| style="border:solid black;border-width:1px 1px 1px 1px;" | At<br>85
| style="border:solid black;border-width:1px 2px 2px 2px;" | Rn<br>86
|-
| '''7'''
| style="border:solid black;border-width:1px 1px 1px 1px;" | Fr<br>87
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ra<br>88
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ac-No<br>89-102
| style="border:solid black;border-width:1px 1px 1px 1px;" | Lr-Cn<br>103-112
| style="border:solid black;border-width:1px 1px 1px 1px;" | Nh<br>113
| style="border:solid black;border-width:1px 1px 1px 1px;" | Fl<br>114
| style="border:solid black;border-width:1px 1px 1px 1px;" | Mc<br>115
| style="border:solid black;border-width:1px 1px 1px 1px;" | Lv<br>116
| style="border:solid black;border-width:1px 1px 1px 1px;" | Ts<br>117
| style="border:solid black;border-width:1px 1px 1px 1px;" | Og<br>118
|-
| ''Group''
| ''(1)''
| ''(2)''
|
| ''(3-12)''
| ''(13)''
| ''(14)''
| ''(15)''
| ''(16)''
| ''(17)''
| ''(18)''
|-
| colspan=14 style="border:none;"|
|-
| colspan=14 style="border:none; text-align:Center;font-size:105%;"| The [[Kainosymmetry|first-row anomaly]] strength by block is '''s''' >> '''p''' > '''d''' > '''f'''.<ref>[[#Jensen|Jensen 1986, p. 506]]</ref>{{efn|Helium is shown above beryllium for electron configuration consistency purposes; as a noble gas it is usually placed above neon, in group 18.}}
|}
Starting with hydrogen, the [[Kainosymmetry|first row anomaly]] primarily arises from the electron configurations of the elements concerned. Hydrogen is notable for its diverse bonding behaviors. It most commonly forms covalent bonds, but it can also lose its single electron in an [[aqueous solution]], leaving behind a bare proton with high polarizing power.<ref>[[#Lee|Lee 1996, p. 240]]</ref> Consequently, this proton can attach itself to the lone electron pair of an oxygen atom in a water molecule, laying the foundation for [[acid-base chemistry]].<ref>[[#Greenwood|Greenwood & Earnshaw 2002, p. 43]]</ref> Moreover, a hydrogen atom in a molecule can form a [[hydrogen bonding|second, albeit weaker, bond]] with an atom or group of atoms in another molecule. Such bonding, "helps give [[snowflake]]s their hexagonal symmetry, binds [[DNA]] into a [[double helix]]; shapes the three-dimensional forms of [[protein]]s; and even raises water's boiling point high enough to make a decent cup of tea."<ref>[[#Cressey|Cressey 2010]]</ref>

Hydrogen and helium, as well as boron through neon, have small atomic radii. The ionization energies and electronegativities among these elements are higher than the [[periodic trends]] would otherwise suggest.

While it would normally be expected, on electron configuration consistency grounds, that hydrogen and helium would be placed atop the s-block elements, the significant first row anomaly shown by these two elements justifies alternative placements. Hydrogen is occasionally positioned above fluorine, in group 17, rather than above lithium in group 1. Helium is almost always placed above neon, in group 18, rather than above beryllium in group 2.<ref>[[#Petruševski|Petruševski & Cvetković 2018]]; [[#Grochala|Grochala 2018]]</ref>