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Chapter 4
section 1
Introduction to Atoms
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.
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.
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