Transcript Parts of the Atom

The Atom
Two major parts of an atom
Nucleus
(not to scale)
Electron
Cloud
Three Major Sub-Atomic
Particles
Protons
 Neutrons
 Electrons

THE PROTON
•Heavy = 1 amu
+
p
• Positive + 1 charge
• Location: Nucleus
THE NEUTRON

°
N
• Heavy = 1 amu
• No charge, neutral
• Location: Nucleus
THE ELECTRON
•Very light = 1/2000 amu
e
• Negative  -1 charge
• Location: electron cloud
Where are they located?
Nucleus:
Protons and Neutrons
Electron Cloud:
Only Electrons
ATOMIC NUMBER (Z)
The # of protons in an atom
 Can not change for an element
 All atoms are neutral, so Z equals the #
of electrons
 For an ion – the number of electrons
may differ

Example: Sodium
Atomic # = # of protons
11
Na
MASS NUMBER (A)
 The
mass of an atom
 A = protons + neutrons
 To
determine # of neutrons
 Neutrons
=A-Z
Example
 An
atom of sodium has a mass of
24 amu, how many protons,
electrons and neutrons does it
have?
11 p+
11
11 eNa
24 - 11 = 13
N°
ISOTOPES
Atoms
of the same
element that differ in
mass.
(They have the same # of
p+, but different # of N°)
Isotope Notation
Mass #
Atomic #
Isotope Notation

Can also be written as
ELEMENT – MASS #

Example: Carbon - 12
So, why do the
elements on the PT
have masses with
decimals???
AVERAGE ATOMIC MASS
The
weighted average
mass of all naturally
occurring isotopes of an
element.
Example using exam scores!
Exam Scores can be weighted higher than homework
or quiz grades:
What if…
Exam 50%
Quizzes 20%
Homework 30%
And you received:
Exam 93
Quizzes 82.5
Homework 85
Your grade =
(93 x .5) + (82.5 x .2) + (85 x .3) = 88.5
Example

Example: The element hydrogen has three
isotopes. It exists in nature 99.41% of the
time as Hydrogen-1, 0.4% of the time as
Hydrogen-2 and 0.19% of the time as
Hydrogen – 3. What is the average atomic
mass of hydrogen?
0.9995*1 + 0.004*2 + 0.001*3 = 1.0078 u
Famous
Scientists in
Atomic Theory
Democritus (400 B.C.)
 First
to
develop the
idea of an
atom.
DALTON

Dalton created an atomic theory that
stated:
All elements are composed of tiny 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

J.J. Thomson
“Plum Pudding Model”
 Solid positively charged sphere
 Electrons embedded within

Rutherford’s Gold Foil Experiment
Rutherford
Proved the existence of a tiny, dense,
positively charged nucleus.
 The rest of the atom is mostly empty
space.
