When you say Utopian socialism, this means that you are looking at things in a more “idealist” manner. There are certain things that you feel can be possible even if they are not exactly realistic at that time. When people use Utopian socialism, they base what they say on their own opinions on what they think could happen and not exactly what might happen.
When you say Scientific socialism, this means that there are some socialist goals that are available, but they can be achieved in a more violent manner. In Scientific Socialism, there are even some historical forces that may be involved in making some of the goals come true.
Utopian socialism is often described as the demonstration of outlines for the present and future societies with positive ideals being the primary reason for guiding society on such a path. Scientific socialism is a bit more contrived. It means that a society ruled by a scientific government that depends on reason and practicality, rather than swayed by opinion or feelings. Karl Marx offered a new vision called capitalism, which bridged the gap between utopian and scientific socialism.
One of the biggest criticisms of utopian socialism is that most of its ideas were founded before the industrial revolution. They were unable to identify with class struggle, which is the backbone of all modern socialist thinking. Scientific socialism is not entirely a science in the way that chemistry and physics are. It is a perspective that entails modern thinking.