SNP Westminster leader Ian Blackford said it was a "disgrace" Boris Johnson was not present, noting he had only appeared at one Prime Minister's Questions since July, as he accused him of "running scared from this chamber".
Mr Johnson's "Brexit fantasy", he said, was an "unacceptable" deal and "doomed to failure".
He said: "Has the Prime Minister not learnt his lesson, he is not above the law. Can the foreign secretary confirm ... that the Prime Minister will not obey the law?
"Is this Government seriously planning to take on Parliament in the courts to force through a catastrophic no-deal Brexit or will the foreign secretary now rule that out?"
Mr Raab replied: "Of course this Government will always adhere to the law ... we want to take forward the negotiations, we want to avoid a no-deal scenario and actually rather than undermine the negotiations in Brussels.
"I'd urge the SNP to try and support the Government in securing a deal, which is good for this country."
Mr Raab called on the SNP to respect the "judgement of the people of Scotland when it comes to staying in the UK and the judgement of the people of the UK to give effect to the referendum on the EU".
Mr Blackford replied: "We will always respect legal judgement."
He called on Opposition MPs to unite, adding: "This Government must be stopped. I am looking now at colleagues on Opposition benches and I urge them we must unite, we must stop this Prime Minister by removing him from office.
"The SNP stand ready to bring this Government down, other parties need to step up at this moment of national crisis. Prepare a vote of no confidence, ensure a Brexit extension, prevent a no-deal and call a general election. Doing nothing is not an option. We must act."
He added: "It is not a case of if, but when we will bring this dangerous Government down."
Mr Raab replied: "He's at risk of sounding like he's all mouth and no trousers because he had the chance to vote for a general election and he turned it down.
"He had the chance to avoid no-deal and the best chance now is to back this Government in securing a good deal, good for the UK and good for all quarters of the UK, including the people of Scotland."
Mr Blackford has meanwhile called on opposition parties in Westminster to unite to remove Mr Johnson from Downing Street.
The party's Westminster leader told MPs during PMQs the SNP "stand ready" to "bring this dangerous Government down".
He urged Opposition MPs to "step up at this moment of national crisis" to "prepare a vote of no confidence, ensure a Brexit extension, prevent a no deal and call a general election".
Liberal Democrat leader Jo Swinson has rejected the possibility of Labour's Jeremy Corbyn becoming a caretaker prime minister.
Mr Blackford called on opposition MPs to unite, adding: "This Government must be stopped. I'm looking now at colleagues on opposition benches and I urge them we must unite, we must stop this Prime Minister by removing him from office."