Download Chapter 4 Atomic Structure

Atomic Structure
Defining the Atom
Structure of the Nuclear Atom
• I CAN identify and describe the particles that
form an atom.
Defining the Atom
EARLY MODELS OF THE ATOM
• An ATOM is the SMALLEST PARTICLE of an
ELEMENT that RETAINS its identity in a CHEMICAL
REACTION.
– The Greek philosopher DEMOCRITUS was one of the
first people to suggest the existence of the ATOM.
– Democritus described atoms as INDIVISIBLE and
INDESTRUCTIBLE.
• Early ideas of the atom DID NOT CATCH ON
because the philosophers COULD NOT TEST
their ideas.
• More than 2000 YEARS passed before the idea
of the atom became an accepted reality.
– JOHN DALTON, an English teacher/chemist, used
EXPERIMENTAL methods to test DEMOCRITUS’
ideas about the atom.
Dalton’s Atomic Theory
• Dalton formulated FOUR STATEMENTS that
formed the basis of the modern idea of the
atom:
– All ELEMENTS are composed of ATOMS.
– ATOMS of the SAME element are IDENTICAL.
– ATOMS can COMBINE CHEMCIALLY to form
COMPOUNDS.
– ATOMS keep their IDENTITY during CHEMICAL
REACTIONS.
Sizing Up the Atom
• Atoms are EXTREMELY SMALL!
– A COPPER PENNY contains approximately
2.4 x 1022 atoms of copper.
– The population of the Earth is approximately
7.0 x 109 (7 billion) people.
– THEREFORE there is about 4,000,000,000,000
[4 TRILLION] times more ATOMS IN A COPPER
PENNY than there are people on the Earth!
STRUCTURE OF THE NUCLEAR ATOM
SUBATOMIC PARTICLES
(NOTE- While there are 17 Fundamental Particles identified – 6 Quarks, 6 Leptons,
4 Gauge Bosons and the Higgs Boson - and over 200 combination particles, we will
focus on only three basic subatomic particles, since we can explain about 99% of
all basic chemistry using these three particles)
• Atoms are composed of THREE BASIC PARTICLES known as
SUBATOMIC PARTICLES.
• ELECTRONS were first discovered in 1897.
– Electrons have a NEGATIVE electrical charge.
– Electrons have a VERY SMALL MASS. It takes 1837 electrons to
weigh as much as ONE PROTON.
– The symbol for an electron is
e-
[note it’s lower case!]
• PROTONS were first discovered in 1886.
– Protons have a POSITIVE electrical charge.
– Protons have a mass about 1837 times larger than
ELECTRONS.
– The symbol for a proton is
upper case!]
P+
[note the P is
• NEUTRONS were discovered in 1932.
• Neutrons have NO ELECTRICAL CHARGE (they
are NEUTRAL)!
• Neutrons have a mass ONLY SLIGHTLY
GREATER THAN a proton.
0
• The symbol for neutron is N [note it is upper
case!]
THE NUCLEUS AND ELECTRON CLOUD
• PROTONS and NEUTORNS are found in the NUCLEUS of
the atom.
– The nucleus is the SMALL, DENSE and SOLID central core
of the atom.
– More than 99.9% of the mass of an atom is located in the
NUCLEUS.
• The atom’s ELECTRONS are found in an area
SURROUNDING THE NUCLEUS known as the ELECTRON
CLOUD.
– The electron cloud can be compared to BEES SWARMING
AROUND A HIVE and it mostly just an area of EMPTY SPACE
where as the nucleus is a SOLID structure.
ATOMIC NUMBER
• Protons play an extremely important role in the atom.
• The NUMBER OF P+ determines the atom’s elemental
identity.
– Each different element on the PT has a unique number of P+ in
its nucleus.
• The NUMBER OF P+ in the atom’s nucleus is known as the
ATOMIC NUMBER.
• In a NEUTRAL ATOM (one that has not reacted with other
atoms) the ATOMIC NUMBER is also equal to the NUMBER
OF ELECTRONS the atom has.
• ATOMIC NUMBER is abbreviated simply as “AN”.
• ANs are WHOLE, SEQUENTIAL numbers found at the top of
each element’s box on most periodic tables.
ATOMIC MASS NUMBER
• Along with the atomic number, the subatomic particles of
an atom contribute to other numbers.
• One important one is the ATOMIC MASS NUMBER,
abbreviated as “AMN”.
• As it’s name implies, it represents the MASS OF ONE ATOM.
The unit for AMN is a derived unit known as the ATOMIC
MASS UNIT, or simply “amu” or more simply “u”.
• The AMN is calculated by adding the total number of
PROTONS and NEUTRONS in the atom together.
• On the Periodic Table, the AMN is generally on the top or
bottom of each element’s box (depends on the PT you
use) and, with only a few exceptions, is a number WITH A
DECIMAL.