Download Helpful Science Notes Chapter 4.2 The Structure of an Atom

Accelerated / Advanced Science 8
Helpful Science Notes
Chapter 4.2
The Structure of an Atom
Vocabulary:
1. Proton
2. Electron
3. Neutron
4. Atomic number
5. Mass number
6. Isotopes
The Structure of an Atom
Properties of Subatomic Particles
Protons
o
Positively charged subatomic particle found in the nucleus of an atom.
o
Assigned a 1+ charge.
Electrons
o
Negatively charged subatomic particle that is found in the space outside the
nucleus.
o
Electron comes from the Greek word meaning “amber.”
o
Has a charge of -1, and a mass approximately 1/2000 of a proton.
Neutrons
o
Discovered in 1932 by English physicist James Chadwick.
o
A neutron is a subatomic particle that is found in the nucleus of an atom.
o
It has a mass almost exactly equal to that of a proton.
Atomic Number and Mass Number
Atomic Number
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Accelerated / Advanced Science 8
o
Equal to the number of protons in the nucleus of an atom.
o
Atoms of different elements have different numbers of protons.
o
The number of electrons usually equals the number of protons.
Mass Number
o
The sum of the number of neutrons and protons in the nucleus of an atom.
o
Number of neutrons = Mass number – Atomic number
Isotopes
Atoms of the same element that have different numbers of neutrons.
For example, every atom of oxygen has 8 protons. Some have 8 neutrons for a mass
number of 16. Others have 9 neutrons for a mass number of 17.
Example: heavy water (Figure 12, page 112)
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