Download PH Chem Chap 4 -- Atomic Structure

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Atomic Structure
Defining the Atom
Defining the Atom
Essential Question
How did the concept of the atom move
from philosophy to science?
Defining the Atom
• An atom is the smallest particle of an
element that retains its identity in a
chemical reaction.
Philosophy or Science?
• Democritus believed that matter
consisted of tiny, indivisible,
unchangeable particles called
• Until recent centuries the existence
of the atom was a philosophical
question rather than a scientific one.
Philosophy to Science
• Greater accuracy in measurement
allowed for experiments which
indicated the existence of atoms.
• Law of Conservation of Mass, Law
of Definite Proportions, and Law of
Multiple Proportions were clues to
the existence of atoms.
Dalton’s Atomic Theory
• 1) All elements are composed of tiny
indivisible particles called atoms.
• 2) Atoms of one element are
identical. The atoms of one element
are different from those of any other
Dalton’s Theory (cont.)
• 3) Atoms of different elements can
physically mix together, or can
chemically combine in simple wholenumber ratios to form compounds.
• 4) Chemical reactions occur when
atoms are separated, joined, or
rearranged. Atoms of one element,
however, are never changed into atoms
of another element as a result of a
chemical reaction.
Sizing Up the Atom
• A copper penny contains about
2.4 x 1022 atoms.
• Earth’s population measures
about 6 x 109 people.
• There are about 4 x 1012 times as
many atoms in a penny as people
on the earth.
Sizing Up the Atom
• A line of 100,000,000 copper atoms
side by side would be only 1 cm
Sizing Up the Atom
• Sizes of atoms are expressed in
picometers (trillionths of a meter).
• 1 cm is the same fractional part of
600 miles as 100 picometers is of 1
Sizing Up the Atom
• Dry air contains 0.002% Neon.
• Yet there are about 5 x 1017 atoms
of Neon in every breath you inhale!
• That’s 500,000,000,000,000,000
Sizing Up the Atom
• In Summary:
• Atoms are itty-bitty.
Atomic Structure
Structure of the Nuclear Atom
Structure of the Nuclear
Essential Question
What are the three principle sub-atomic
particles and what part do they play in the
structure of the atom?
The Structure of the
Nuclear Atom
• Atoms are known to be divisible.
• Sub-atomic particles include
neutrinos, quarks, baryons, hadrons,
fermions, bosons, mesons, leptons,
photons, gravitons, gluons,
electrons, protons and neutrons.
• Not to mention futons, croutons,
Nissans and morons.
The Structure of the
Nuclear Atom
We will be most concerned with
protons, neutrons and electrons.
Subatomic Particles
The Electron
• Discovered by Thomson
• Negatively charged particles
• Relative charge = 1–
• Symbol = e–
• 1 / 1840 the mass of a proton
• Reside outside of the nucleus
Subatomic Particles
The Proton
• Discovered by Goldstein
• Positively charged particles
• Relative charge = 1+
• Symbol = p+
• Mass of 1 atomic mass unit (amu)
Subatomic Particles
The Neutron
• Discovered by Chadwick
• Neutrally charged particles
• Relative charge = 0
• Symbol = n0
• Mass of 1 atomic mass unit (amu)
The Atomic Nucleus
• Discovered by Rutherford (Gold Foil
• The tiny central core of an atom
• Composed of protons and neutrons
The Atomic Nucleus
• The nucleus is highly compacted
and extremely dense.
• Most of the mass of atoms is in the
• Nuclei have a density of about
2 x 108 metric tons / cm3 !
Atomic Structure
Distinguishing Among Atoms
Distinguishing Among
Essential Question
What part do protons, neutrons and electrons
play in the identity and characteristics of
Atomic Number
• The number of protons determines
the identity of the element.
• The number of protons is indicated
by the atomic number.
Mass Number
• The mass number indicates the
number of protons AND neutrons in
the nucleus.
• How do you find the number of
neutrons from the mass number of a
given element?
• Isotopes are atoms of that have the
same number of protons (the same
element) but have different numbers
of neutrons.
• They, therefore, have different mass
numbers and different masses.
Atomic Mass
• Masses of atoms are incredibly
small and impractical to express in
• It is more practical to compare the
masses of atoms to a different
Atomic Mass Unit
• An AMU (atomic mass unit) is
defined as 1/12 the mass of a
Carbon-12 atom.
• Since the Carbon-12 atom is made
up of 6 protons and 6 neutrons, an
AMU is approximately equal to the
mass of one proton or one neutron.
Atomic Mass
• An element’s atomic mass is a
weighted average mass of all the
atoms in a naturally occurring
sample of the element.
• To calculate atomic mass, multiply
the mass of each isotope by its
percent abundance (expressed as a
decimal) and add the products.