Science Starter: Black Boxes Groups of 2: Manipulate the box so the marble moves around the fixed...
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Transcript of Science Starter: Black Boxes Groups of 2: Manipulate the box so the marble moves around the fixed...
Science Starter: Black Boxes
Groups of 2: Manipulate the box so the marble moves around the fixed object inside of the box.
DO NOT OPEN THE BOXDiscuss what the object in the box might look like.On the science starter page, sketch the object in the box, showing its size, shape and location within the box.
Time for Activity: 10 minutes
Thomson’s Atomic Model
Thomson: electrons were like plums embedded in a positively charged “pudding”
• the “plum pudding” model
J. J. Thomson
Ernest Rutherford’sGold Foil Experiment - 1911
Alpha particles (helium nuclei) were fired at a thin sheet of gold foil Particles that hit on the detecting screen (film) are recorded
Rutherford’s Findings
a) The nucleus is smallb) It is densec) It is positively charged
Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected
“Like howitzer shells bouncing off of tissue paper!”
Conclusions:
The Rutherford Atomic Model• Based on his experimental evidence:
–The atom is mostly empty space–All the positive charge, and almost all
the mass, is in the center• “nucleus”
–The nucleus is composed of protons and neutrons
–The electrons are distributed around the nucleus and occupy most of the volume• “nuclear model”
Section 4.3Distinguishing Among Atoms
Atomic Number• Atoms are composed of identical
protons, neutrons, and electrons• Elements are different because they
contain different numbers of PROTONS• The “atomic number” of an element is
the number of protons in the nucleus
• # protons in an atom = # electrons
Element # of protons Atomic # (Z)
Carbon 6 6
Phosphorus 15 15
Gold 79 79
Look at the periodic table to confirm these numbers
Mass NumberMass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0
Nuclide p+ n0 e- Mass #
Oxygen - 10
- 33 42
- 31 15
8 8 1818
Arsenic 75 33 75
Phosphorus 15 3116
This mass # may not match the mass # on the periodic table
Complete Symbols
• Include the symbol of the element, the mass number and the atomic number.
X Massnumber
Atomicnumber
Subscript →
Superscript →
Symbols Find each of these:
a) number of protons
b) number of neutrons
c) number of electrons
d) Atomic number
e) Mass Number
Br80 35