Lavoisier made a list of thirty-three elements. His list of elements challenged the age-old idea that
elements are made of atoms.
there are only four elements.
elements cannot be identified
elements do not exist in the free state.

He challenged the idea of Phlogiston; that it was in fact not something trapped in flammable things, it was a gas (Oxygen) that allowed some things to burn.

Explanation:

He took a Mercury Oxide, in a glass vessel; he heated it with a magnifying glass to yield Hg and O2.

5 structural isomers

the isomers are:

n-exane :   ch3ch2ch2ch2ch2ch3

2-methylpentane :   ch3ch(ch3)ch2ch2ch3

3-methylpentane :   ch3ch2ch(ch3)ch2ch3

2,3-dimethylbutane :   (ch3)2chch(ch3)2

2,2-dimethylbutane :   (ch3)3cch2ch3