1. section 1 Introduction to Atoms
Chapter 4
section 1
Introduction to Atoms

2. Introduction to Atoms Development of atomic Theory
Dalton’s atomic theory: Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.
Thomson’s model suggested atoms had negatively charged electrons embedded in a positive sphere
Rutherford’s model suggested atoms have positively charged nucleus.
Bohr’s model suggested electrons have specific orbits.
Cloud model suggested that electrons move rapidly in every direction around the nucleus.

3. Key Terms Atom is the smallest particle of an element.
Electron A negatively charged particle that is found outside the nucleus of an atom has a mass of almost zero .
Proton is a positively charged particle that is part of an atom’s nucleus it has a mass of 1amu.
Neutron is a small particle in the nucleus of the atom, with no electrical charge, it has a mass of 1amu.
Nucleus is the central core of the atom that contains protons and neutrons.
Energy level is the specific amount of energy an electron has.

4. The Modern Atomic Model
At the center of the atom is a tiny, massive nucleus containing protons and neutrons. Surrounding the nucleus is a cloudlike region of moving electrons.
Atomic Number is the number of protons in the nucleus of the atom.
Isotopes are atoms of the same element that have different number of neutrons.
Mass number is the sum of protons and neutrons in the nucleus of the atom.
Atomic Mass is the average mass of all the isotopes of an element