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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