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 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