Chapter 3: The Mole - The Central Unit of Chemistry Flashcards
object with more mass contains _____ particles, compared to an object of less mass
larger
def: a ration of one object’s mass to that of another object
relative mass
what is the one essential criteria for determining the relative mass between two objects?
both groups of objects contain the same number of objects
what assumptions are we making when we determine relative mass?
that all the objects in one group are identical to each other in mass
def: all samples of a given compound contain the same elemental composition by mass, meaning their elements are always present in a fixed ration
law of constant composition
who presented the theory that “atoms of different elements combine in simple whole-number ratios to form compounds”?
john dalton
what was wrong with Dalton’s theory that atoms combine in simple whole number ratios?
he assumed that elements ALWAYS combine in the simplest possible ratio
what were two parts to Dalton’s atomic theory?
- atoms of a given element are identical to each other, but different from those of other elements
- atoms of different elements combine in a simple whole-number ratio to from compounds
you can determine absolute values directly, while relative values require _______________
comparing to a second value
what element did Dalton assign the atomic mass unit to?
hydrogen as it is the least massive
def: a dimensionless ratio of the average mass of an element’s atoms compared to an agreed upon and consistent reference
relative atomic mass
Ar
what is our current reference for relative atomic mass?
the carbon-12 atom
what did Cannizzaro’s paper clear up?
that some elements don’t exist as individual atoms when alone, they exist as diatomic molecules
def: seven elements whose particles are homonuclear diatomic molecules, rather than individual atoms
diatomic element
def: describes a molecule formed of identical atoms
homonuclear
