Use the macro below to write a sulfate ion like this:

The font is Arial size 11, unlike the font produced by Equations using the method here. Put the macro on the Quick Access Toolbar then type 21 for the sulfate ion, 22 for nitrate and 23 for carbonate.
Sub SymbolsByBigAl()
'make popup box
10 Dim Message, Title, MyValue
Message = "enter the atomic number (1-20 only)" & Chr(13) & Chr(10) & "21 = sulfate" _
& Chr(13) & Chr(10) & "22 = nitrate" & Chr(13) & Chr(10) & "23 = carbonate"
Title = "Big Al's symbol generator"
'deal with inputs
MyValue = InputBox(Message, Title, MyValue)
If MyValue = 1 Then GoTo 100
If MyValue = 2 Then GoTo 200
If MyValue = 3 Then GoTo 300
If MyValue = 4 Then GoTo 400
If MyValue = 5 Then GoTo 500
If MyValue = 6 Then GoTo 600
If MyValue = 7 Then GoTo 700
If MyValue = 8 Then GoTo 800
If MyValue = 9 Then GoTo 900
If MyValue = 10 Then GoTo 1000
If MyValue = 11 Then GoTo 1100
If MyValue = 12 Then GoTo 1200
If MyValue = 13 Then GoTo 1300
If MyValue = 14 Then GoTo 1400
If MyValue = 15 Then GoTo 1500
If MyValue = 16 Then GoTo 1600
If MyValue = 17 Then GoTo 1700
If MyValue = 18 Then GoTo 1800
If MyValue = 19 Then GoTo 1900
If MyValue = 20 Then GoTo 2000
If MyValue = 21 Then GoTo 2100
If MyValue = 22 Then GoTo 2200
If MyValue = 23 Then GoTo 2300
If MyValue = "" Then GoTo 5000
'deal with wrong inputs
BeepMsg "you were told to choose 1 to 23, numpty"
GoTo 10
'write symbols
100 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="1"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="1"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="H"
GoTo 5000
200 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="2"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="4"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="He"
GoTo 5000
300 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="3"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="7"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Li"
GoTo 5000
400 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="4"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="9"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Be"
GoTo 5000
500 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="5"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="11"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="B"
GoTo 5000
600 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="6"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="12"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="C"
GoTo 5000
700 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="7"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="14"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="N"
GoTo 5000
800 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="8"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="16"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="O"
GoTo 5000
900 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="9"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="19"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="F"
GoTo 5000
1000 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="10"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="20"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Ne"
GoTo 5000
1100 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="11"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="23"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Na"
GoTo 5000
1200 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="12"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="24"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Mg"
GoTo 5000
1300 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="13"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="27"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Al"
GoTo 5000
1400 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="14"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="28"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Si"
GoTo 5000
1500 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="15"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="31"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="P"
GoTo 5000
1600 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="16"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="32"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="S"
GoTo 5000
1700 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="17"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="35"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Cl"
GoTo 5000
1800 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="18"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="40"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Ar"
GoTo 5000
1900 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="19"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="39"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="K"
GoTo 5000
2000 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add Range:=Selection.Range, Type:= _
wdOMathFunctionScrPre
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="20"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="40"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="Ca"
GoTo 5000
2100 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add(Selection.Range, _
wdOMathFunctionScrSubSup).ScrSubSup.AlignScripts = False
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="SO"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="4"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="2-"
GoTo 5000
2200 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add(Selection.Range, _
wdOMathFunctionScrSubSup).ScrSubSup.AlignScripts = False
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="NO"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="3"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="-"
GoTo 5000
2300 Selection.OMaths.Add Range:=Selection.Range
Selection.OMaths(1).Functions.Add(Selection.Range, _
wdOMathFunctionScrSubSup).ScrSubSup.AlignScripts = False
Selection.MoveLeft Unit:=wdCharacter, Count:=3
Selection.TypeText Text:="CO"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="3"
Selection.MoveRight Unit:=wdCharacter, Count:=1
Selection.TypeText Text:="2-"
GoTo 5000
5000
'sort out italics and font
Dim equation As OMath
For Each equation In ActiveDocument.OMaths
equation.Range.Font.Italic = False
Next equation
Selection.WholeStory
Selection.Font.Name = "Arial"
End Sub