Unit:
The Atom
and
The Periodic Table
Evolution of the Structure of an
Atom
Dalton’s Atomic Theory
• All elements are composed of indivisible
particles called atoms
• Atoms of the same element are identical. The atoms of
any one element are different from those of any other
element.
• Atoms of different elements can physically mix together
or chemically combine with one another in simple whole
number ratios to form compounds.(law of definite
composition)
• Chemical rxns occur when atoms are separated, joined,
or rearranged. Atoms of one element, however, are
never changed into atoms of another element as a result
of a chemical reaction.(law of conservation of mass)
J.J. Thomson
• discovered the electron
• plum pudding model
Rutherford
• discovered the nucleus
• Proposed electrons surround
the nucleus in a cloud
The Atom Today
• The atom is the smallest particle of an element that
retains the properties of that element
• Atoms can only be seen with proper
instrumentation
• Dalton’s Atomic Theory wasn’t completely
correct
• Atoms can be broken down into subatomic
particles
• Atoms of the same element are not identical
Properties of Subatomic Particles
Particle
Electron
Proton
Nuetron
Symbol
Relative Charge
Relative Mass
Actual mass (g)
Distinguishing Between Atoms
Atomic Number
• Number of protons in the
nucleus of an atom
• Identifies the element
• Elements are listed on periodic
table according to atomic
number
Atomic Number
Atomic Number
Atomic Number
• atoms are electrically neutral
• # protons = # electrons
Mass Number
• total number of protons and
neutrons in an atom
• It is not found on the periodic
table but can be estimated
Shorthand Notation
Fill in the following table
Isotopes
• Atoms that have the same
number of protons but different
numbers of neutrons
• Differ in their mass number
Isotopes
• the existence of isotopes was
not predicted by Dalton, who
said atoms of the same element
are the same
Isotopes
• identified by their mass # ,
write the name of the element
then a hyphen with the mass
number
Isotopes
Uses of Isotopes
• C-14 = archeological carbon
dating
• Am-241 = smoke alarms
• I-131 = treating thyroid disorder
• Co –60 = cancer treatment
Atomic Mass (atomic weight)
• weighted average mass of the
atoms in naturally occurring
samples of the element
Atomic Mass
• reflects the mass and the
relative abundance of isotopes
as they occur in nature
Atomic Mass
• To calculate the atomic mass of an element
multiply the atomic mass of each isotope of the
element by its relative abundance, then add the
results
atomic mass = mass1relabd.1 + mass2rel.abd.2+...
1. Calculate the % abundance of fictitious element Nv
2. If the mass of 293Nv is 293.15 amu (red)and that of 295Nv is
295.15 amu (blue), what is the atomic mass of Nv?
.
Periodic Table
• _______________ was the first
person to find a way to list
elements in order of increasing
atomic mass
Periodic Table
• He constructed the first periodic
table in 1869, an arrangement
of the elements according to
similarities in their properties.
Mendeleev’s Periodic Table
Periodic Table
• In 1913, ______ determined the
atomic number of atoms and
arranged the modern periodic
table according to atomic
number .
Modern Periodic Table
Modern Periodic Table
• Each element is identified by its
symbol placed in a square
Modern Periodic Table
• The horizontal rows of the
periodic table are called _____
• There are ___
Modern Periodic Table
Modern Periodic Table
• Each vertical column is called a
____ or ____
• There are ____.
Modern Periodic Table
Periodic Table
• A periodic law means that physical
and chemical properties of
elements are functions of their
atomic numbers
• Elements in the same group on the
periodic table have similar
properties
Modern Periodic Table
• Group A elements are called the
representative elements because
they have a wide range of
chemical and physical
properties
• Name the groups in Group A
Modern Periodic Table
• Group B elements are called the
______________
• The inner transition elements
are the ______ and _____
Modern Periodic Table
Modern Periodic Table
• The representative elements can
be divided into three broad
classes; Metals, Nonmetals, and
Metalloids
• What are some characteristics
of each?
Modern Periodic Table
Niels Bohr
• credited for a model of the atom
that states that electrons are at
specific distances from the
nucleus of an atom
Bohr Models
Energy Level
# ELECTRONS
1
2
3
4
Bohr Models
Exception: Outermost energy
level can only hold up to 8eYou need to be able to diagram
Bohr models for 1-36;
excluding transition elements
Bohr Models
Do you notice any trends with
the group or period of the
periodic table?
Bohr Models
Trends:
1. Group numbers (1-8A) predict
valence electrons (electrons in the
outmost level).
2. The period tells you how many
energy levels you have in the
atom.