3919 The Crooked Man by Jago

A well-crafted puzzle -- albeit one that could have definitely used a better-written preamble.

As per the theme word ELEMENTARY, across entries, all originally too long for their spaces in the grid, were to be "adapted" to fit by the use of symbols for chemical elements. This meant that a number of across answers' letters were to be entered in lowercase; those letters were then ignored entirely by intersecting down answers. And any possible ambiguities were ruled out by the proviso that none of the elements in the grid could be TRANSURANIAN.

The unclued entries HOLMES, WATSON, and CONAN DOYLE tied the theme word ELEMENTARY to the title, as Holmes did say "Elementary" in The Crooked Man.

Across entries are given as they were entered in the grid.

ACROSS
2 Theme word
ELEMENTARY
10 Such language from Bananarama? I cringed! (7)
ARaMAIC (...arama I C... hidden)
The theoretically possible ARAmAIC could be eliminated because Am (americium) is transuranian. It could also be eliminated on the grounds that elementary symbols were to be used wherever consecutive letters could form a symbol while still fitting in the grid, and the first possibility here was Ra (radon); however, this fact about the puzzle probably would not have been immediately obvious.
11 A mountain to climb? Half of obstacle cleared by this famous character (6, two words)
BeN HUR (BEN + HURdle)
12 Peeing in river with little sibling (6)
UReSiS (URE + SIS)
13 As an author did talk up prose novel (7)
PURPOsE (UP PROSE anag.)
14 Fighting very much like boy -- one at club, showing no resistance (12)
DIGLaDIAtION (DIG + LAD + I + AT + IrON)
17 Identify Eastern poem (with help) when travelling West (8)
DIAgNOsE (E + SONG + AID rev.)
18 Unclued
HOLMES
20 Searches for stolen goods: smuggled Turkish instruments? (7)
RaNZELS (RAN + ZELS)
25 Half of seal and headless rodent seen in sewer (8)
SeAMSTeR (SEal + hAMSTER)
26 Unclued
WATSON
27 To be specific: all good alcohol initially must be exported from Riga, Latvia reprocessed (7)
TRIVIAl (RIGA LATVIA - A G A anag.)
28 Wild West: a lost, unsettling place (13)
OsWAlDTWISTlE (WILD WEST A LOST anag.)
32 Money-making knowledge (8)
LEARnInG (L + EARNING)
34 Rising high without quite finishing drug (7)
AsPIrIn (ASPIRINg)
35 Oh dear ... a Midwest state? No, it's a different state that this refers to (7)
AlAsKAN (ALAS + KAN (Kansas))
36 Staggeringly near tons ... many North Americans fit such a description! (8)
NORTeNAs (NEAR TONS anag.)
37 Unclued
CONAN DOYLE

DOWN
1 Wary old man getting mixed up with a French cleaning lady (12)
LAUNDRYWOMAN (WARY OLD MAN anag. about UN)
2 Mistake going on river right away -- it makes your nose run (7)
ERRHINE (ERR + rHINE)
3 Put drainage channels to south without ... without complication? Just the opposite (8)
EASINESS (EAS + S around SINE)
4 Component of Single Currency (3)
ECU (...e Cu... hidden, &lit.)
5 Anorak found in Tyneside street?
NERD (NE + RD)
6 An ox, not crossed with a wild ox (4)
ANOA (AN + Ox + A)
7 Cathedral city of a cardinal in the borders (6)
RHEIMS (HE (His Eminence) in RIMS)
8 Expression of disgust at ordinary throw, worth only five points (4)
YUKO (YUK + O, ref. judo)
9 Iran bans natural regeneration -- though parts of lab disappear -- but such things cannot be natural (12)
TRANSURANIAN (IRAN BANS NATURAL - LAB anag.)
15 The French vessel is inferior (4)
LESS (LE + SS)
16 Island press article's not right (4)
IONA (IrON + A)
19 Licensed to beg, I try, messing about with alms I then lose a shilling (8)
LIMITARY (I TRY ALMS I - S anag.)
21 Device for cutting up stolen goods (4)
LOOT (TOOL rev.)
22 Italian drink, it's one from the south (4)
ASTI (ITS A rev.)
23 Noxious gas coming from food container in old pigpen (7)
STIBINE (BIN in STIE)
24 Idle gentleman appearing to hunt nothing (6)
STALKO (STALK + O)
29 Female combatant with a mate on Merseyside (4)
WAAC (WACK homophone, ref. Women's Army Auxiliary Corps)
30 Martin -- noted for singing -- found in small valley (4)
DEAN (double definition, ref. Dean Martin)
31 This bird might be 29's mate (4)
WREN (double definition, ref. Women's Royal Naval Service)
33 Country that takes some finding (3)
IND (...fINDing hidden)