Atoms & Their StructureChapter 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

one-twelfth 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