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Dalton believed believed elements are
minute, indivisible particles called atoms.
Dalton believed atoms of the same element are alike in
mass and sizes
Dalton believed Atoms of different elements have
different masses and sizes
Dalton believed chemical compounds are formed by the union of
two or more atoms of different elements.
Dalton believed Atoms combine to form compounds in simple
numerical ratios (such as 1-1, or one to 2, or 2 to 3 and so on).
Dalton believed two elements may combine in different ratios to form
more than one compound
Law of definite composition
a compound always contains two or more elements in a definite proportion by mass
Law of multiple proportions
Atoms of two or more elements may combine in different ratios to produce more than one compound.
What do the laws of multiple and definite composition state:
1) the composition of a particular substance will always be the same no matter what its origin or how it is formed.
2) the composition of different compounds formed from the same elements will always be unique.
A law is
a summary of observed behavior
A model/theory is
an attempt to explain the observed behavior.
subatomic particles are
electrons protons and neutrons
what is the nucleus
contains protons, neutrons and electons
what's the atomic number
number of protons
valies in the loss or gain (#) of neutrons, but has the same amount of protons/atomic number.
mass number is
the neutrons+ protons=mass number
mass of an electron compared to proton
1/1837 amu, with neg charge
mass of a proton
1.673 X10^-24 g w/positive charge
mass of neutron and it's charge
1/1.675X10^-24 g, with no/neutral charge
an atom that lost or gained an electron (having +/- charge).
Thomson's model of atom
negative electrons are embedded in positive atomic sphere.
Rutherford's model of the atom
atoms are composed of protons and neutrons surrounded by electrons which occupy mostly empty space.
6 parts of Dalton’s
- are composed of minute indivisible particles called atoms.
- of the same element are alike in mass and size.
- of different elements have different masses and sizes.
- compounds are formed by the union of two or more atoms of different elements.
- combine to form compounds in simple numerical ratios, such as one to one, two
- to two, two to three, and so on.
- of two elements may combine in different ratios to form more than one compound.
Properties of electrical charges
•Charge may be of two types:
_______ and ______.
•Unlike charges ________t (positive
attracts negative), and like charges repel (negative repels negative and
positive ______ positive).
•Charge may be transferred from one
________ to ________, by ________ or __________.
•The less the distance between two
charges, the _______ the force of attraction between ______ charges (or
_______ between identical charges).
- •Charge may be of two types:
- positive and negative.
- •Unlike charges attract (positive
- attracts negative), and like charges repel (negative repels negative and
- positive repels positive).
- •Charge may be transferred from one
- object to another, by contact or induction.
- •The less the distance between two
- charges, the greater the force of attraction between unlike charges (or
- repulsion between identical charges).
Who discovered ions
- Faraday discovered that certain
- substances, when dissolved in water, conducted an electric current.
Why did he call them ions
- •He found that atoms of some
- elements moved to the cathode (negative electrode) and some moved to the anode
- (positive electrode).
- •He concluded they were electrically
- charged and called them ions (Greek wanderer).
what were Rutherford's findings regarding uranium
- He studied the emission of rays from uranium (alpha and beta rays:
- •If a positive alpha particle approached close enough to the positive mass in the gold foil it was deflected.
•Most of the alpha particles passed through the gold foil. This led Rutherford to conclude that a gold atom was mostly empty space.
Rutherford's contribution to understanding the atom:
- •atom had a dense, positively charged nucleus.
- •a light,negatively charged electrons were present in an atom and offset the positive nuclear charge.
Chadwick’s contribution to understanding the atom:
- work in 1932 demonstrated the atom contains neutrons.
How do these numbers relate to describing an element:
Top left, Bottom left, and element symbol.
- *Mass number=top left (protons+neutrons),
- *atomic number=bottom left/proton number,
- *Element symbol=proton number