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PHYSICAL EARTH SCIENCE
CHAPTER 4: ATOMS AND THE PERIODIC TABLE
Section 1: Atomic Structure
What are Atoms?
1. Our understanding of atoms required many centuries
a. Atom- derived from Greek word meaning “unable to be divided”
b. Democritus – 4th century BC philosopher – first to suggest units of
atoms
c. 1700s science put more emphasis on accuracy and repeatable
experiments – resulted in better data collection
2. John Dalton developed an atomic theory
a. 1808 English schoolteacher – proposed his theory
b. Proposed that atoms could not be divided (today we know differently)
c. Proposed all atoms of one element were the same
d. Proposed different atoms could join to form compounds
e. Considered the foundation of the modern atomic theory
3. Atoms are the building blocks of molecules
a. Atom – smallest part of an element that still hold’s all of the elements
properties
b. Atoms can join to form molecules
What’s in an Atom?
1. Atoms are made of protons, neutrons, and electrons
a. Nucleus of an atom
i. In center of atom
ii. Contains Protons (positively charged) - Nearly same size and
mass as neutrons
iii. Contain Neutrons (neutrally charged – no charge)
b. Outside of nucleus – rings of electrons (e-) – negatively charged –
very little mass
2. Unreacted atoms have no overall charge
a. Atoms have an equal number of protons and electrons – balancing out
the overall charge of the atom
Models of the Atom
3. Bohr’s model compares electrons to planets
a. 1913 Danish scientist
b. Suggests electrons move in pathways around the nucleus – like
planets around the sun
c. States that e- have certain amount of energy according to their orbit
d. Gain or lose energy – move up or down energy levels
e. Still accurate description today
2. Electrons act more like waves
a. 1925 new model suggests electrons behave more like waves on a string
4. An electron’s exact location cannot be determined
a. Electron’s are moving too fast to be able to tell where or how fast
they are going at any particular moment
5. Electrons exist in energy levels
a. E- with different amounts of energy are on different energy levels
b. The # of filled energy levels depends on the total # of ec. Energy levels contain a maximum of e-:
i. Energy level 1 = 2eii. Energy level 2 = 8eiii. Energy level 3 = 18eiv. Energy level 4 = 32e6. Electrons are found in orbitals within energy levels
a. Orbitals – the region in an atom that an e- is most likely to be found
b. S orbital – simplest kind of orbital; shape like a sphere; lowest energy
and can hold 2ec. P orbital – dumbbell shape; can be oriented 3 different ways; has
more energy than s; can hold 6ed. D orbital – 5 possible orientations; can hold max 2ee. F orbital – 7 possible orientations; has most energy; can hold max 2e7. Every atom has between one and eight valence electrons
a. Valence e-  e- in outermost energy level
i. Determine an atoms chemical properties
ii. Determines atom’s ability to form bonds
Section 2: A Guided Tour of the Periodic Table
Organization of the Periodic Table
1. Groups similar elements together
2. Periodic Law – states that the repeating chemical and physical properties of
elements change periodically with the atomic numbers of the elements
3. Elements are represented by their symbols
4. Arranged in order according to the number of protons an atom of that
element has in its nucleus
5. Periodic Table – pg 112-113
6. The Periodic table helps determine electron arrangement
a. Periods – horizontal row in periodic table
b. Number of protons and e- increases by one as you move from L to R
7. Elements in the same group have similar properties
a. Elements that have the same # of valence e- have the same chemical
properties
Some Atoms Form Ions
1. Atoms that don’t have outer s and p orbitals filled may gain or lose e- to
complete the orbitals
2. An ion forms when the electrons and protons don’t balance out and the
atom has a +/- charge
3. A lithium atom loses one electron to form a 1+ charged ion
a. Losing 1 e- mean there are more protons than e-  causing a positive
charge
4. A fluorine atom gains one electron to form a 1- charged ion
a. Adding an e- adds a negative charge and means there is one more
negative than there are positive causing a net negative charge
How Do the Structures of Atoms Differ?
1. Atomic number equals the number of protons
2. Mass number equals the total number of subatomic particles in the nucleus
a. # of Protons + # of Neutrons = Mass Number
3. Isotopes of an element have different numbers of neutrons
4. Some isotopes are more common than others
a. IE. Protium (hydrogen isotope); tritium
5. Calculating the number of neutrons in an atom
a. Mass Number – Atomic Number = Number of Neutrons
6. The mass of an atom
a. Expressed in atomic mass units (amu) b/c mass is SO small
b. Atomic mass listed in table is usually an average
Section 3: Families of Elements
How Are Elements Classified?
1. Elements are classified into three groups
a. Metals – shiny solids that can be stretched/shaped; good conductors
of heat/electricity
b. Nonmetals – solids/liquids/gases on rt. side of table; dull/brittle and
poor conductors
c. Semiconductors – nonmetals that conduct under certain
circumstances
Metals
1. The alkali metals are very reactive
a. Soft, shiny
b. Reacts violently to water b/c it has a valence e- that is easily
removable
c. Not found in nature – usually combine w/other element to form
compounds – ie. Salt is NaCl
2. Alkaline-earth metals form compounds that are found in limestone and in
the human body
a. Have 2 valence e- making them less reactive
b. Strong materials – like calcium and Mg
3. Gold, silver and platinum are transition metals
a. Located in groups 3-12 in periodic table
b. Not found combined – found in nature pure
c. Even less reactive
d. Conduct heat/electricity
e. Very useful in today’s society
4. Technetium and promethium are synthetic elements
a. Synthetic – means man-made
b. Both are radioactive – nuclei of their atoms are continually decaying
to produce different elements
c. All elements w/atomic numbers greater than 92 are man-made
Nonmetals
1. Carbon is found in three different forms and can also form many
compounds
a. Found on Rt. side of table
b. Carbon combines with many other elements creating millions of
compounds
2. Nonmetals and their compounds are plentiful on Earth
a. IE. Oxygen, nitrogen, sulfur
3. Chlorine is a halogen that protects you from harmful bacteria
a. Located in group 17
b. Strong smelling – kills bacteria
c. Very reactive – forms compounds easily
4. The noble gases are inert
a. Exist as single atoms instead of molecules
b. Inert – means un-reactive
i. Noble gases are un-reactive b/c they don’t need any e-  their s
and p orbitals are full
5. Semiconductors are intermediate conductors of heat and electricity
a. Also called metalloids and clustered on right side of table
b. Have some properties of metals
i. Able to conduct heat/electricity under certain conditions
6. Silicon is the most familiar semiconductor
a. Silicon atoms/compounds are 28% of the Earth’s mass – IE. Sand
Section 4: Using Moles to Count Atoms
Counting Things
1. There are many different counting units
2. The mole is useful for counting small particles
a. Abbreviated  mol.
b. A collection of over 600 million trillion particles – VERY LARGE
c. Usually written 6.022 X 10 23mol. and is referred to as Avogadro’s
constant
3. Moles and grams are related
a. The mass of 1 mol of a substance is called molar mass
Calculating with Moles
1. Using conversion factors
a. Usually you have to multiply by a conversion factor
2. Relating amount to mass
a. An element’s molar mass can be used as if it was a conversion factor
3. Converting moles to grams