Chess-oriented crossword puzzle

Difficulty: moderate.

Answers so far:

Across: 5.Mephisto, 8.Gedult, 10.Brady, 11.Sveshnikov, 13.Nakamura, 15.Rook, 16.Composer, 19.Center, 20.Bishop

Down: 1.Sodium, 2.Capablanca, 3.Morphy, 4.King, 6.Algebraic, 7.Chain, 9.Golombek, 12.Castling, 14.Al Lajlaj, 17.Material, 18.Scotch

19 across is center.
18 down is Scotch.

3 down is Morphy.
17 down is material.

4 down is pawn.
12 down is castling.

All correct so far, except 4 down - it is not "pawn"!

 Correct!

I'm going to answer one of the more difficult ones (IMO):

13 Across: Nakamura

If the crossword is filling slowly I shall return. 

4 down is king.

10 Across:  Brady

5 across mephisto

All answers correct!

11 across is Sveshnikov.

2 down capablanca?

"Sveshnikov" is correct!

20 across Bishop?

14 Down: Al Lajlaj

9d golombek

Capablanca for 2 maybe

Again all correct!

8 acrross, is it gedult?