DALTON’S ATOMIC THEORY UNIT #2 THE ATOM

Background At the time of John Dalton, chemists had this basic understanding: Elements react with other elements to form compounds Elements cannot be broken down into other substances They had no idea that atoms (the individual particles that make up matter) and elements and compounds were related Dalton drew this connection between atoms and elements and compounds

Inspiration from Proust’s work Dalton, after reviewing Proust’s research, hypothesized that elements were made up of different types of atoms  the type of atom determined the element Compounds were combinations of these elements which had reacted

Evidence for Dalton’s conjecture After Dalton discovered the Law of Multiple Proportions, he was convinced his hypothesis about atoms were true The Law of Multiple Proportions is the following: When two elements react to form different compounds, the ratios of the second element combined with one gram of the first element can be reduced to whole number ratios

Illustrating the Law of Multiple Proportions   Mass of Nitrogen Mass of Hydrogen Compound A 1 g 0.144 g Compound B 0.216 g Compound C 0.024 g

How does this data relate to atoms?

Dalton’s Atomic Theory Consists of four postulates All matter is composed of small, indivisible particles called atoms All atoms of the same element are the same, and all the atoms of different elements are different Atoms break apart and rearrange themselves to form new substances Atoms combine in simple, whole number ratios to form compounds

Dalton’s Flaws