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The Development of the Theory of the Atom
THE INDIVISIBLE ATOM
GREEK – DEMOCRITUS (450 BC)
1. Atom was _________________________
2. Theorized the _______________________ of the atom
3. Also, theorized that there were just four 'elements' - _______, _______, _______, and _______.
JOHN DALTON (1803)
1. Atom was _______________________
2. All _____________________ are composed of atoms
3. The same atoms for one element are __________________________ alike
4. Atoms are neither created nor destroyed in a ________________________.
5. In a chemical reaction, atoms are ____________________________,
_________________________, or _______________________________.
THE DIVISIBLE ATOM
J. J. THOMASON (1897)
1. discovered the _________________ using the cathode ray tube.
2. determined that the electron was smaller than a __________________ atom.
3. Knew the atom was _____________ and the electron was ___________________, so there must
be positive material with a lot more mass.
4. Said the atom was a _______________________________ material throughout which
_________________ charged electrons were scattered - Plum Pudding or Chocolate Chip
Cookie Model.
ERNEST RUTHERFORD (1909)
1. Did a famous gold foil experiment (the _____________ __________________ experiment)
2. Calculated that the atom was mostly ___________________ through which ________________
move.
3. Concluded that the atom has a __________, dense, _________________ charged,
_________________-located nucleus surrounded by negatively charged _______________.
ERNEST RUTHERFORD (1919)
1. Called the positive particles ____________________.
ERNEST RUTHERFORD and JAMES CHADWICK (1932)
1. showed the nucleus also had ______________________
2. The neutron was basically equal in mass to the proton but had _______ ____________________
charge.
NEILS BOHR (1914)
1. Concluded that ________________ moved around the nucleus in definite orbits or
___________________________.
DALTON REVISITED
1. Atom was indivisible. _____________
2. All elements are composed of atoms. _____________
3. The same atoms for one element are exactly alike. _____________
4. Atoms are neither created or destroyed in a chemical reaction. _____________
5. In a chemical reaction, atoms are separated, combined, or rearranged. _________
THE CURRENT ATOM
 is ___________________ shaped
 with a dense, centrally located, positive nucleus containing _____________ and
__________________.
 surrounded by one or more negatively charged ________________ in an electron cloud.
 Most of the atom’s _______________ consists of fast moving electrons traveling through the
_______________________ that surrounds the ________________.
 Electrons are held within the atom by an ______________________ to the positive nucleus.
 The nucleus has _____________ neutrons and _______________ protons and _____________
of the mass.
 Since atoms are electrically neutral, the ______________ of protons must ______________ the
number of electrons.
ATOMIC STRUCTURE
ELEMENT: One of the __________ known _____________ substances. Listed on the periodic table.
ATOM: ______________________ piece of matter that still retains the properties of that matter.
______________________ in the world is made of atoms.
NUCLEUS: _________________ of the atom; _________________ of the mass of the atom; contains
_______ particle types; has a _______________________ charge.
ELECTRON CLOUD: Surrounds the _____________________; Contains _______ particle type; Has
a ____________________ charge.
1. PROTON, p+: All are _____________________, regardless of the element. Location:
________________; Charge ______________________; Relative mass ______________
2. NEUTRON, n: All are _____________________, regardless of the element. Location:
________________; Charge ______________________; Relative mass ______________
3. ELECTRON, e-: Location: ________________; Charge ______________________; Relative mass
______________; Number in an atom: number of electrons = __________________ protons
(neutral atom)
What makes one element different from another element? ____________________________________
IMPORTANT NUMBERS
ATOMIC NUMBER, Z: equals the number of ________________________________;
determines the ____________________ of the element; On the periodic table, starts at
__________ and goes up in order; It is the “5” in the symbol to the right.
ATOMIC MASS: the ____________________ of the masses of the isotopes of an atom;
the ______ on the periodic table; IT IS ________ the masses of the protons, neutrons,
and electrons added together!
MASS NUMBER, A: the number of __________________ and ___________________
(nucleons) added together; take the ______________________ (round!) of the atomic
mass to get the mass number; It is the “11” in the symbol to the right; Also can be
written after the element’s name: _________________________.
HOW DO YOU DETERMINE THE NUMBER OF…..
PROTON
NEUTRON
ELECTRON
REMEMBER:
 The atomic number of an element _______________ changes.
 The number of protons is __________________ the same.
 The number of ______________________________________________ can change and the
element is still the same element.
===============================================================
PRACTICE:
1. How many protons and electrons are present in a vanadium atom?
________
2. How many protons and electrons are present in a nitrogen atom?
________
3. How many protons and electrons are present in an argon atom?
________
4. What is the name of the element that has atoms that contain 5 protons? ____________
5. How many protons, neutrons, and electrons are present in zirconium-91?
protons _____
neutrons _____
electrons _____
6. How many protons, neutrons, and electrons are present in cesium-140?
protons _____
neutrons _____
electrons _____
7. What is the atomic number and the mass number for the element with 27 protons and 32
neutrons? Atomic # ______
Mass # ______
8. What is the atomic number and mass number for the element with 84 protons and 125
neutrons? Atomic # ______
Mass # ______