Presentation on theme: "Warm-up 1/24/08. PS-2.2 Illustrate the fact that the atoms of elements exist as stable or unstable isotopes."— Presentation transcript:
PS-2.2 Illustrate the fact that the atoms of elements exist as stable or unstable isotopes.
The atomic number of an element is equal to the number of protons. The atomic number is always the same for a given element. The atomic number of an element can be found on the periodic table.
Atoms of the same element may have different numbers of neutrons. The mass number of a particular atom is the sum of that atoms nucleons (protons and neutrons).
The mass number cannot be found on the periodic table. The mass number is not the same as atomic mass and cannot be found by rounding off atomic mass.
The Atomic mass of an element as seen is the weighted average of the masses of the naturally occurring isotopes of an element. The atomic mass of an element can be found on the periodic table. Since it is an average, it is usually not a whole number.
Isotopes are defined as two or more atoms of the same element having the same number of protons but different numbers of neutrons (and therefore different masses) H – 1 H – 2 H – 3
Mass Number Atomic Number Atomic Symbol
In order for a nucleus to be stable, there must be enough neutrons present to block the repulsive forces among the protons. An unstable isotope of an element is radioactive.
Home Work Define Chapter 17 Vocabulary 15 terms on p. 530