Chapter 4

1. 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 of1amu. • 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