Particles of Matter Chapter 1.3

Atom The smallest particle of an element.

John Dalton British school teacher In 1802 he proposed an atomic theory Dalton tested his ideas by carrying out experiments

Dalton’s Atomic Theory 1 Atoms can’t be broken into smaller pieces Dalton imagined atoms to be like tiny marbles or rigid spheres that are impossible to break

Daltons Atomic Theory 2 In any element, all the atom are exactly alike This idea explains why an element always has the same properties

Dalton’s Atomic Theory 3 Atoms of different elements are different This idea explains why different elements have their own set of properties

Dalton’s Atomic Theory 4 Atoms of two or more elements can combine to form compounds Compounds can be broken down into elements, so Dalton concluded that compounds had to be made of atoms.

Dalton’s Atomic Theory 5 Atoms of each element have a unique mass. Dalton and other scientists of his day were not actually able to measure the mass of individual atoms

Dalton’s Atomic Theory 6 The masses of the elements in a compound are always in the same ratio Water is a compound composed of hydrogen atoms and oxygen atoms, always in the ratio 2 hydrogen to 1 oxygen.

Atoms Atoms are super tiny One grain of sand has more atoms than there are grains of sand on the entire beach A drop of water has 2,000,000,000,000,000,000,000 atoms of oxygen and twice as many atoms of hydrogen There is now a scanning tunneling microscope that can capture what atoms look like

Atom and Molecules Atoms can link with each other. A chemical bond holds two atoms together. A molecule is a combination of two or more atoms that are bonded together Example: Water molecule, acetic acid molecule (C2H4O2)