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Ch. 4 - Atomic Structure
I. Structure of the Atom Dalton’s Atomic Theory
Subatomic Particles
A. Dalton’s Atomic Theory
Every element is made of tiny, unique, particles called atoms that cannot be subdivided.
Atoms of the same element are exactly alike.
Atoms of different elements can join to form molecules.
B. Subatomic Particles
POSIT IVECHARG E
PROT ONS
NEUT RALCHARG E
NEUT RONS
NUCLEUS
NEG AT IVE CHARG E
ELECT RONS
AT OM
Most of the atom’s mass.Atomic Numberequals the # of...
in a neutral atom
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
ATOM
B. Subatomic Particles
B. Subatomic Particles
Atoms have no overall charge because the protons (+) cancel out the electrons (-).
Neon 10 protons = +10 10 neutrons = 0 10 electrons = -10 total charge 0
Ch. 4 - Atomic Structure
II. Electron Cloud Model Orbital
Energy Levels
Bohr Model Diagrams
B. Energy Levels
Electrons can only exist at certain energy levels.
Low energy levels are close to the nucleus.
Each energy level (n) can hold a certain number of electrons.
A. Orbital
Region where there is 90% probability of finding an electron.
Can’t pinpoint the location of an electron.
Density of dots represents the probability.
C. Bohr Model Diagrams
Simplified energy levels using Bohr’s idea of circular orbits.
e-
e-
Maximum e-
Level 1 2e-
Level 2 8e-
Level 3 18e-
Level 4 32e-
Lithium Atomic #: 3 Mass: 7
# of p: 3 # of e: 3 # of n: 4
p
pn
nn n
p
e-
Can replace with:
3p4n
C. Bohr Model Activity
Choose a number between 1 & 18. Find your element by the atomic number you picked. Draw a Bohr Model diagram for your element on your marker board.
• Round off the atomic mass listed on the table and subtract the atomic # to find the # of neutrons.• Abbreviate the # of ‘p’ and ‘n’ in the nucleus.
Have a partner check your drawing. Repeat with a new element.
Ch. 4 - Atomic Structure
III. Masses of Atoms Atomic Mass
Mass Number
Isotopes
A. Atomic Mass
atomic mass unit (amu) – unit of measurement
Average atomic mass – the average mass of all the isotopes of the atom.
© Addison-Wesley Publishing Company, Inc.
B. Mass Number
Sum of the protons and neutrons in the nucleus of an atom.
Always a whole number.
# of neutrons = mass # - atomic #
© Addison-Wesley Publishing Company, Inc.
C. Isotopes
Atoms of the same element with different numbers of neutrons.
C126Mass #
Atomic #
Isotope symbol:
“Carbon-12”
C. Isotopes
© Addison-Wesley Publishing Company, Inc.
