Class 2 chem 403

Smallest unit of a substance

substances consisting of a single kind of atom

ex. oxygen, gold, iron

a substance formed by a combination of 2 or more elements bonded together

2 or more atoms bounded together

the total weight of substances remains constant during a chemical reaction

In a compound the mass fraction of each element is always the same

Ex. water always contains 88.8% oxygen and 11.2% hydrogen by mass

• ratio of elements in a compound.
• Expressed as 2 or more elements to other are in a ratio of small whole numbers when 2 or more compounds are formed

John Dalton

• 1. Matter is composed of atoms that cannot be created or destroyed
• 2. Atoms of one element can not be converted in atoms of another element
• 3. Atoms of an element are identical in mass and other properties but add different but add different from atoms of any other element (This meants that atoms of one element weigh more than the atoms of another element)
• 4. Compounds result in from the chemical combination of a specific ratio of different elements

equals the # of protons in the nucleus

the # of electrons and the atomic #

neutrons

number of protons

the # of PROTONS + # of ELECTRONS

atomic weight

relative abundance of different isotopes of an element is measured using an intrument

the sum of isotope mass times abundance of isotope fro all naturally occurring isotopes