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what is an atom

the smallest particle of an element that has a unique identity in a chemical reaction
what parts of dalton's theory do we not believe to be true
- atoms indivisible
- not the same (different number of neutrons)
describe 4 main points to early atomic theory
- philosophers believed atoms were INDIVISIBLE & INDESTRUCTABLE
- no scientific method at this part in time
- good idea but no supporting data
- early 1800's moved from ideas to scientific theory
cathode ray experiment
- passed electric current through low pressure gas contained in tube
- ray attracted to (+) charged plate and repelled (-)
describe how electrons were discovered
- ratio charge: mass of particles
- ratio same every element
why did scientists begin to look for a positive particle
- charges were always whole numbers
- there was a neutral charge
- had to balance out negative charge
what kind of particles found in nucleus

subatomic particles
plum pudding model
- electrons are like plums evenly distributed throughout
- protons are the pudding, lump of positive charge
nuclear model of atom

tiny central core of atom composed of protons and neutrons
6
Li
3
- neutrons: 3
- protons: 3
- electrons: 3
7
Li
3
- neutrons: 4
- protons: 3
- electrons: 3
atomic #

# of protons
mass #

# of protons + # of neutrons
isotopes
- atoms with the same number of protons but different number of neutrons
- same atomic number
- different mass number
why do isotopes behave the same chemically

protons & electrons are responsible for chemical behavior and they are always the same
how to calculate atomic mass

[(% abundance as decimal)*mass]
group
- column
- elements in a group have similar chemical & physical properties
period
- row
- properties vary as you move across a period, but there's a pattern of properties that repeats
- *%#
- *%#
- *%#

Author

emilyyx14

112439

Card Set

chemm

Description

chem

Updated

2011-10-27T01:03:23Z

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