The Atom
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Transcript of The Atom
The Atom
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
Atoms are Indivisible and Indestructible? Not true!
Why? Nuclear reactions Subatomic particles
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
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
Neutrons Discovered by Chadwick No charge Same mass as proton (1) Found in the nucleus of an atom
Atomic Number Whole number Atomic # = # of proton Atomic # = # of electrons
(neutral) Atomic # = Z
Shorthand nuclear symbol Unique for every element
Atomic Number
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)
Mass Number
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
Nuclear Shorthand
Top number is A (mass #) Element symbol in the
middle Bottom number is Z (atomic
#)
Z
AElement Symbol
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
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
Very Funny… but what is wrong with this?
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
Isotopes
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
Cations and Anions