The Atom. Basic Atomic Theory Atom = “indivisible” in Greek Atoms are indivisible and...
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Transcript of The Atom. Basic Atomic Theory Atom = “indivisible” in Greek Atoms are indivisible and...
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The Atom
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Basic Atomic Theory
Atom = “indivisible” in Greek Atoms are indivisible and
indestructible Atoms of same element are
identical Compounds are formed by a
combination of two or more different kinds of atoms
Chemical reactions cannot change one element into another Atoms only rearrange
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Atoms are Indivisible and Indestructible?
Not true!
Why? Nuclear reactions Subatomic particles
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Electrons
Discovered by J.J. Thompson using a cathode ray tube
Negatively charged (-1) Electron’s mass is 1/1840 Free moving around the
nucleus
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Protons Discovered by Moseley Positively charged (+1) Proton’s mass is 1 (About 2000 times more
than an electron) Atomic # = # protons
No 2 elements have the same # of protons
Found in the nucleus of an atom
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Neutrons Discovered by Chadwick No charge Same mass as proton (1) Found in the nucleus of an atom
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Atomic Number
Whole number Atomic # = # of proton Atomic # = # of electrons
(neutral) Atomic # = Z
Shorthand nuclear symbol
Unique for every element
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Atomic Number
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Mass Number
Whole number Mass # = # of protons + # of
neutrons Mass # = A
Shorthand nuclear symbol Isotopes of the same element
have different mass # Isotopes are the different kinds of
atoms within one element (C-12 and C-13)
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Mass Number
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Using Mass Number
Mass # = # of protons + # of neutrons
To find # of protons # protons = # electrons (neutral
atom) Need to know mass # and # of
neutrons To find # of neutrons:
Need to know mass # and # of protons
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Nuclear Shorthand
Top number is A (mass #) Element symbol in the
middle Bottom number is Z (atomic
#)
Z
AElement Symbol
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Atomic Mass
Listed on periodic table Does not equal mass # Given in atomic mass units
(amu) 1 amu = 1/12 the mass of C-12
atom Is not a whole number
Due to relative abundance of naturally occurring isotopes Weighted average
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Finding Atomic Mass
To calculate the atomic mass of an element Multiply the mass of each isotope
by its percent abundance (expressed as a decimal) The quantity of a specific isotope that
occurs in a natural sample of an element Add the masses together
Also called average atomic mass
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Very Funny… but what is wrong with this?
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Isotopes Atoms of the same element
Have the same # of protons and electrons
Have a different number of neutrons Have a different mass number
Have the same physical and chemical properties and undergo the same chemical reactions
Have differing nuclear qualities Some isotopes of an element may be
radioactive Average atomic mass takes all of
the isotopes into consideration
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Isotopes
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Ions
Atoms are neutral Equal number of protons and
electrons Atoms can become charged by
gaining or losing an electron Called ions
Ions are indicated with a (+) or (-) sign Cations are positive Anions are negative
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Cations and Anions