I have adapted this page from my biology curriculum. The screenshot shows what I did for biology, but you can just as easily use this system for chemistry.
Here's a sample of how you could break things down and assign grade percentages to total up a final grade. Having said that though, YOU have to decide the right grading system for your family. This is just what *I* have done, in the past, with my children.
One thing I've used to keep track of our homeschool and to help with grading is Homeschool Tracker. Homeschool Tracker is great at doing all of the below for me automatically. I just tell it how I want it to weight subject activities and it calculates everything out for me. There are other homeschool record keeping programs available that can do this or, you could just write things out on paper, the old fashioned and FREE way. ;-)
This is the grading scale I use:
F 69 and below (sorry, no D's!)
The above is a screenshot from Homeschool Tracker showing how I've assigned grading weights for biology: The 2nd column is points possible. The 3rd column shows points earned. The 4th column shows the average. The 5th column shows the current letter grade. The 6th column shows the weighted value. This screenshot was taken after just the first week of our biology program but it shows you how Otter was earning his biology grade. Some things he did were totally ungraded and not reflected in the grade averages above.
The picture to the left shows how Homeschool Tracker calculates Otter's grade. In this example there were 47 questions for him to answer in his workbook. He got 44 questions correct. His grade is 94%, an A.
Here's an online points possible calculator you can use.
Here's a breakdown of activities you can use to calculate your student's grade:
Classwork / Participation: 15%
This percentage is based on Otter's participation and attitude during the time he is working on his assignments. I expect him not to whine or complain about any activity, not to dawdle and to answer questions I ask him during our read-aloud time or activities thoughfully and age-appropriately (no "I dunno" answers accepted). For the chemistry curriculum, this includes clean-up of the kitchen after the cooking projects.
Printables / Study Guide: 25%
This grade is pretty straight forward. I mark off for spelling errors (a quarter to half point) in some situations if the words are available in the material he's working from.
Activities & Projects: 25%
Otter was graded on how well he followed instructions, the quality of his work, etc. I wouldn't grade the end result of a cooking project, as there will likely be some failures. Use those as learning experiences. I would, however, grade the effort put into them.
Other Assignments (reading, writing, quizzes, videos, etc.): 35%
This category includes getting reading assignments done in a timely manner, watching and discussing videos, computer assignments, etc. Each item is to be graded according to quality of work, etc.
Feel free to adjust the percentages to reflect what you would like your student to focus on! The above is just an example.