The solution to this element crossword challenge [1] is 299, obtained by adding all the atomic numbers of elements that appear in the grey squares:

F, B, O, C, O, Ar, N, N, As, O, In, V, K, O, Re, S:

9 + 5 + 8 + 6 + 8 + 18 + 7 + 7 + 33 + 8 + 49 + 23 + 19 + 8 + 75 + 16 = 299

Across: 1 Saucer-like disks in the sky? 5 Light at hand 7 Reserve to attend 10 Mafia is an example of these 11 Total ruin 13 One who relocates 15 Cut finely 17 Overhead glow, possibly 19 Neither homo nor hetero 20 Like this 22 In for a row 23 Made in a skillful way 26 Looks like fire’s remains 28 Prefix with -logism 29 Not that 30 A kind of mile 31 Short for a unique identifier 32 Unsuitable 33 Not far 34 Traditional performing artists of Japan 37 A piercing for the flow 39 High altitude region in near the city of 71 down 40 One who seeks penalty 43 Unit of a whole 44 Land animals you don’t want to see approaching with a hood 46 Another name for an equine 47 Award Walt Disney got most often 48 Founders of the Kingdom of Cusco 50 Means to direct water to the gutter 51 As of suffix 52 Valuable ground 54 Release the beast 56 How you may want your chips (2 words) 59 Bone substance for food or adhesives 61 Often considered a social construct in the social sciences 62 Cobbler for a 46 across perhaps 65 Modern bait tries to make you this 66 Exhibit when with case 67 First-timer 68 Condition of absence of a force 69 Airplane section for cargo e.g. 70 Single stockings 71 Fights or cages 73 A sudden thrust of a foot 74 Center part 75 One who adds the color 76 More like 2 down 79 A social group or elegance 82 Exerted for the fun of it 84 Anagram and possibly article of a billion years 85 Possibly the couture of a 65 down 87 Kind of question 90 Feel 91 Used to avoid—or await—entry 92 Often accompanying a 70 down 93 Named periods.

Down: 1 Prefix with score, path, way, lie 2 Some imagination 3 Tuber from southern America 4 Multiplied it can make a process 5 What you may not want to get back 6 Starting point when approaching liftoff 7 Less painful than the cause of an 81 down usually 8 Not required or included 9 Anti-knock, low-mass paraffin 10 A polished surface’s appearance 11 Deity of old, considered a false one 12 In short: Memory in NASAs first manned lander 14 Multiple 16 One forcefully captured 18 Surprise! 21 African queen 23 As(III)-acid 24 Much less large 25 Dissolving 26 Italian region known for sparklings 27 WWII near end congress city 32 ….facto, 33 Used in the bath, made in the kitchen 35 Not his 36 Acid, initially named after its cure from scurvy 38 Transit sort of 41 Can be ironic or 25 down 42 Holds the door 45 Fresh 46 Santa’s words 49 Not leave alone 53 Done in many labs, but not only there 54 One of the edit options 55 Not calm 57 One with an opinion 58 One with a mental condition 60 Promised not to lie 63 Covers cakes (or cover lakes) 64 Aretha’s command in the Blues Brothers movie 65 Official of the church 67 Obsessive and introverted 69 Foundation 70 Heavy cry 71 Canton in CH 72 minus 18 is its number 77 Better than trash 78 Most shining in Aquila 80 Not in time 81 Remains of a cut maybe 83 Compacts e.g. hay or straw 86 Pure eventually 88 Not day, in slang 89 It’s more and more going electric.