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4.2 THE STRUCTURE OF AN ATOM VOCABULARY:
proton electron neutron
OBJECTIVES: Identify three subatomic particles & compare
their properties.
Distinguish the atomic number of an element from the mass number of an isotope, and use these numbers to describe the structure of an atom.
VOCABULARY: atomic number mass number isotope
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PROPERTIES OF SUBATOMIC PARTICLES By 1920,
evidence for existence of 2 subatomic particles (+ & - charges)
Rutherford predicted existence of 3rd particle
subatomic particles:
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COMPARING SUBATOMIC PARTICLES distinguished by mass, charge, & location
e- charge = in size to, but opposite of, charge of p+
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PROPERTIES OF SUBATOMIC PARTICLES: ELECTRONS negatively (-) charged particles Thomson detected were later named electrons
Electron symbol: e- charge: negatively charged (1-) location: in space outside of nucleus
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Rutherford also concluded that amount of positive (+) charge varies among elements
Proton symbol: p+
charge: positively charged (1+) location: in nucleus of atom
PROPERTIES OF SUBATOMIC PARTICLES: PROTONS
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PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONS Discovered in 1932, by English physicist James Chadwick
designed experiment to show that neutrons exist
concluded that particles he produced were neutral b/c a charged object did not deflect their paths
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PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONSNeutron
symbol: ncharge: neutral (0)location: in nucleus of atom
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soda?
For you… No charge.
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Proton:
Neutron:
Electron:
• Heavy, Positive
• Heavy, Neutral
• Light, Negative
SUBATOMIC PARTICLES
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COMPARING SUBATOMIC PARTICLES everything known about nucleus &
subatomic particles based on how particles behave
Currently, don’t have instrument to show inside of atom, but do have microscopes that show how atoms are arranged on a material’s surface (Page 111)
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ATOMIC NUMBER Atomic number of an element equals the
number of protons in an atom of that element.
i.e. 1 proton in nucleus of every hydrogen atom. Therefore, atomic number of hydrogen = 1.
Atoms of different elements have different number of protons.
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ATOMIC NUMBER
atoms are neutral each + charge in an atom is
balanced by a - charge.
Therefore atomic # of an element also equals # of electrons in an atom.
How many electrons does a hydrogen atom have?
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MASS NUMBER
Mass number - sum of the protons and neutrons in the nucleus of an atom.
i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number?
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MASS NUMBER
Mass number - sum of the protons and neutrons in the nucleus of an atom.
i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number?
13 protons + 14 neutrons = 27
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MASS NUMBER http://web.visionlearning.com/custom/
chemistry/animations/CHE1.3-an-animations.shtml
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MASS NUMBER
If you were given the mass number and atomic number of an atom, how can you find the number of neutrons?
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MASS NUMBER
If you were given the mass number and atomic number of an atom, how can you find the number of neutrons?
Answer: by subtracting atomic # from mass #
# of neutrons = mass # – atomic #
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ISOTOPES
Dalton’s atomic theory: all atoms of a given element are identical
Every atom of a given element DOES have same # of protons & electrons but does not have same # of
neutrons.
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ISOTOPES Isotopes - atoms of the same element that have different numbers of neutrons and different mass numbers.
Therefore, isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.
representation of two isotopes of carbon
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ISOTOPES
Hydrogen atoms: all have 1 proton most have no neutrons and mass #
of 1 (hydrogen 1) some have 1 neutron (hydrogen 2)
or 2 neutrons (hydrogen 3)
http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-
isotopes.shtml http://web.visionlearning.com/custom/chemistry/overheads/CHE1.3-oh-
isotopes.shtml
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ISOTOPES
All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?
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ISOTOPES
All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?
Answer: # of neutrons = mass # – atomic # mass # = 18 atomic # = 8 # of neutrons = 18 – 8 = 10