Atoms
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__________ thought there was NOT a limit to the number of times matter could be divided.
Aristotle
_______________ developed a theory to explain why the elements in a compound always join in the same way.
John Dalton
The main points of John Dalton’s theory are what?
• All elements are composed of atoms. • All atoms of the same element have the same mass, and atoms of different elements have different masses. • Compounds contain atoms of more than one element. • In a particular compound, atoms of different elements always combine in the same way.
_____________ provided the first evidence that atoms are made up of even smaller particles. In his model of the atom, electrons were evenly scattered throughout an atom.
J.J. Thomson
What two items are affiliated with J.J. Thomson?
plum pudding and a cathode ray tube
____________ named uranium particles ______ particles and concluded the positive charge of an atom is NOT evenly spread throughout the atom, it is concentrated in a very small, central are that he called the _________.
Ernest Rutherford, alpha, nucleus
What experiment is Rutherford affiliated with?
gold foil experiment
____________ developed a model of the atom that shows electrons moving with constant speed fixed orbits around the nucleus.
Niels Bohr
Today we know electrons do NOT move like planets around the sun. An _________ is a visual model of the most likely __________ for electrons in an atom.
electron cloud, locations
define isotopes
atoms of the same element that have different numbers of neutrons and different mass numbers
To distinguish one isotope from another, the isotopes are referred to by the __________.
mass number
_________ believed that all matter consisted of extremely small particles that could NOT be divided. He named the particles _________ from the Greek word ________, which means “_______” or “____________.”
Democritus, atoms, atoms, uncut, indivisible
Name the 3 particles of an atom.
proton, neutron, and electron
What is the charge of a proton?
positive
What is the charge of a neutron?
there is no charge, it is neutral
What is the charge of an electron?
negative
The number of protons in one atom of an element determines the atom’s __________ and the number of electrons determines the _______ of an element.
atomic number, charge
The atomic number tells you the number of _________ in one atom of an element. It also tells you the number of _________ in a neutral atom of that element. The atomic number gives the “identity” of an element as well as its location on the Periodic Table. No two different elements will have the _____ atomic number.
protons, electrons, same
The ___________ of an element is the average mass of an element’s naturally occurring atom, or isotopes, taking into account the _________ of each isotope.
atomic mass, neutrons
The ___________ of an element is the total number of protons and neutrons in the _______ of the atom
atomic mass, nucleus
The mass number is used to calculate the number of _________ in one atom of an element. In order to calculate the number of neutrons you must subtract the _______ from the __________.
neutrons, protons, atomic mass