There are several Chrome extensions available that provide tools to block websites. You'll need to choose one; here are a few popular options to aid your research
Block Site - This extension was created by blocksite.co and offers a few features centered around blocking websites both temporarily and permanently.
Site Blocker - This extension is available from Soli Software Inc. It has features for managing blocked websites on a schedule, based on keyword, and more.
Stay Focused - This extension is designed to limit access to specific websites by blocking them with the goal of improving your focus on other tasks. It's owned by Transfusion Media.