Atoms & Their
Structure
Chapter 2 Section 1
Part 3
Objectives
What information is available in an element
block of the periodic table?
Important Vocabulary
Atomic number
Mass number
Atomic mass unit
Atomic mass
Isotopes
The Modern Periodic Table
The modern periodic table has 118 elements
Only 114 have official names
It groups similar elements together
The organization makes it easier to predict
the properties of elements
Elements are represented by their symbols
Position in the table helps to determine
properties of elements
The order of arrangement is based on
the number of protons an atom of that
element has in the nucleus
Reading The Periodic Table
Information from the PT
Atomic number (Z) equals the number of
protons as well as the number of
electrons
Mass number (A) equals the total
number of subatomic particles in the
nucleus
The number of protons & neutrons
Mass number – atomic number = # of
neutrons
The Mass of an Atom
Is very small
We usually work with atomic mass units
Atomic mass unit (amu) is equal to onetwelfth of the mass of carbon-12 atom
Average atomic mass is a weighted average
of the masses of all naturally occurring
isotopes of an element
The more common the isotope the
greater the effect on the average
Isotopes
Are atoms of the same element that
differ by the number of neutrons in the
nucleus
They DO NOT differ in atomic number
They ONLY differ in mass number & their
physical properties
Mass of an Atoms
Calculating the # of Neutrons
Practice!
 Calculate the # of protons, electrons,
& neutrons in the following isotopes
1. Carbon-14
2. Nitrogen-15
3. Sulfur-35
4. Calcium-45
5. Iodine-131
Practice!-Answers
Carbon-14: P = 6
E = 6
N = 8
Nitrogen-15: P = 7
E = 7
N = 8
Sulfur-35: P = 16
E = 16
N = 19
Calcium-45: P = 20
E = 20
N = 25
Iodine-131: P = 53
E = 53
N = 78