Whereas a B.S. degree in chemistry provides you with basic skills and concepts in chemistry, advanced degrees give you the opportunity and experience for developing your own style of research and organizational skills. You are also trained in more specialized areas with a focus on specific research interests. Such training encourages intellectual independence which is essential to postdoctoral and industrial employment. Continuing your education beyond the B.S. degree provides for substantially enhanced opportunities with respect to employment options in industry, government, and academia (college level academic positions are essentially restricted to doctoral level degrees). Career advancement is faster, you are trained (and supervise others) in more specialized areas, and salaries are significantly higher. In addition, you are in almost all cases paid to go to graduate school at levels which provide for a reasonable standard of living and most or all tuition costs are waived. This is warranted by the fact that you typically serve as a teaching assistant for one to two semesters and then as a research associate funded by grants from your research mentor.
Salaries at the Ph.D. level are at least $10-15,000 greater than starting salaries at the B.S. level. The doctoral degree provides the greatest flexibility with respect to career options and advancements. The only real disadvantage which one might suggest for continuing into graduate school is that you are still in a testing environment, time demands are substantially more than at the undergraduate level (expect 45-65 hours/week), and you are waiting an additional 4-6 years to be gainfully employed at respectable wages.
Acceptance into a graduate program in chemistry is not as competitive as one may think. This is clearly indicated by the very competitive stance the schools have taken towards attracting doctoral candidates. Additional incentives such as tuition waivers, health insurance, entry level research stipends, and paid visits to the campuses are common place. Graduate schools are looking for good academic records (GPA >3) and GRE scores, evidence of previous research experience, and good letters of recommendation from your undergraduate faculty.