Unit: Chemistry
Lesson 1: Introduction to
Atoms
Essential Questions:
1.) How did atomic theory
develop?
2.) What is the modern model
of the atom?
How did atomic theory develop?
Atomos “uncuttable”
The smallest particle
of an element
Atom
Dalton
 Atoms cannot be broken into
smaller pieces
Dalton thought
that atoms were
like hard balls that
could not be
broken.
Dalton’s Model
.
Thomson
 Atoms are made of smaller parts
Negatively charged particles
in an atom
Electron
 Atoms contain a positive charge
An atom has electrons
scattered throughout it
like seeds in a
watermelon.
Thomson’s Model
Thomson suggested that atoms had negatively charged electrons set
in a positive sphere. Each electron is represented by the symbol e−.
Rutherford
 An atom is mostly empty space with a
positive center
The center of an atom
Nucleus
Positively charged particles
in an atom’s nucleus
Protons
The pit models the nucleus of an
atom and the fruit is the space
with electrons.
Rutherford’s Model
According to Rutherford’s model, an atom was mostly open space. The
“6+” in the model means that there are six protons in the nucleus.
Bohr
 Electrons are found in specific orbits
Cloud Model
 Electrons move within a cloudlike
region
The amount of energy
an electron has
Energy level
Modern Model of the Atom
Particles in the nucleus
with no electrical charge
Neutron
 An atom has a nucleus made of
positively charged protons and neutral
neutrons. The nucleus is surrounded
by a cloud of negatively charged
electrons.
Modern Model of an Atom
A carbon atom has a nucleus made up of positively charged
protons and neutral neutrons. The nucleus is surrounded by a
cloud of negatively charged electrons.
Particle Charges
Number of protons = number of electrons
Particle Masses
Protons and neutrons make up most of the
mass
The number of protons
in the nucleus
Atomic Number
Atoms with the same
number of protons and
different numbers of
neutrons
Isotopes
The sum of the protons
Mass number
and neutrons in the atom
Isotopes of Carbon
All isotopes of carbon contain 6 protons. They differ in the number of
neutrons. What is the missing information for each isotope?