Chapter 4 Notes
Atoms
Atomic Theories

All scientists believed that all matter
consisted of extremely small particles that
could not be divided called atoms.
Scientists
1. Daltongathered
evidence by
measuring
masses of
elements.
Evidence for
Theory
Models
All matter is
Solid
made of atoms.
Spheres
 Compounds
contain atoms of
more than one
element.
 All elements
have different
masses.
 Atoms of
different elements
always combine in
the same way.

Scientists
2. JJ Thomsonprovided the
first evidence
for subatomic
particles
Evidence for
Theory
Models
Used a sealed
tube of gas and
when the current
was on a glowing
beam appeared.
The beam bent
toward the
positively charged
plate indicating
the beam was
negative.
Plum pudding

Or
Choc. Chip ice
cream
Scientists
3. Rutherforddiscovered the
nucleus by
using a gold foil
experiment
Evidence for
Theory
Models
Nucleuscontains the
protons and
neutrons in the
center of an
atom
Positive &
dense nucleus

Rutherford’s Gold Foil Experiment
Scientists
4. Bohr- agrees
with Rutherford’s
model but he
focused on
electrons and
discovered 4 levels

MODERN
THEORY USED
TODAY
Evidence for
Theory
Models
Discovered energy
levels where
electrons orbit
around the nucleus
 When they move
UP a level they are
in an EXCITED
STATE
 When they move
DOWN they EMIT
ENERGY AS LIGHT
 Each level can
only contain a
certain number of
electrons
Planet Model

Other Models


Electron Cloud Model- used to show
possible location of electrons in an atom.
Electron Configuration- is an arrangement
of electrons in the orbital of an atom
** Most STABLE electron configuration is
when electrons are in the lowest possible
energy levels. This is the GROUND
STATE.
Structure of an Atom

Atoms consist of protons and neutrons in
the nucleus and electrons in the energy
levels surrounding the nucleus.
Particle
Symbol
Charge
Mass
Location
Proton
P+
1+
1
Nucleus
Electron
e-
1-
1/1836
Outside
nucleus
Neutron
N0
No
Charge
1
Nucleus
Structure of an Atom

A. Atomic Number- equals the number of
protons in an element. Found above the
symbol of an element.
Structure of an Atom

B. Atomic Mass- is the mass of the nucleus (equals
#protons + #neutrons)
*** All atoms are neutral with a ZERO CHARGE since
they have the same number of negative and
positive charges.
*** To find the number or neutrons:
Atomic Mass – Atomic Number = Number of neutrons
Structure of an Atom

C. Isotopes – Atoms of the same element
with different numbers of neutrons which
changes the mass number.
** The element on the periodic table is the
one that occurs most readily in nature.
7
N
14.0067
Atoms Quiz
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Which scientist used the gold foil experiment?
Which scientist’s model was the solid sphere
model?
Which scientist discovered the nucleus?
What are atoms?
Which scientist’s theory do we use today?
Opposite charges ________, and like charges
__________.
What is the nucleus?
What are the 3 subatomic particles called?
What charge do electrons have?
How many protons, electrons, and neutrons
does an atom of Magnesium (Mg) have?