How do you write #0.045# in scientific notation?
Move the decimal until you have the smallest whole number you can get.
What ever direction you move the decimal will tell you if it is a positive or negative exponent. In this case it was less than 1, therefore it will be a negative exponent.
Had the number been greater than one, it would've been a positive exponent.
4.5 is called the initial number or coefficient
In writing scientific notations, the initial numbers should follow the General Standard Formula: