Chapter 3-Elements and the Periodic Table
Lesson 1: Introduction to Atoms
Development of the Atomic Theory
• Around 430 B.C. --> Democritus (Greek) proposed matter was made of small particles that
could not be cut into smaller pieces.
• Called “atomos = uncuttable”
• Atom: Smallest particle that can still be considered an element.
• Atomic models and theories grew as more evidence was collected via experimentation.
Dalton’s Solid Sphere Model
• John Dalton--> English chemist --> Came up with Dalton’s Atomic Theory
1) All elements consist of atoms that cannot be divided.
2) All atoms of the same element are exactly alike and have the same mass. Atoms of
different elements are different and have different masses.
3) An atom of one element cannot be changed into an atom of a different element by a
chemical reaction.
4) Compounds are formed when atoms of more than one element combine in a specific
ratio.
Thomson’s “Plum Pudding” Model
• 1897- J.J. Thomson discovered atoms had negatively charged particles --> ELECTRONS
• Reasoned there must be a positive particle to balance the charge.
• Electrons scattered throughout a ball of positive charge --> Like a watermelon
Rutherford’s Nuclear Model
• 1911- Thomson’s former student - Ernest Rutherford - found evidence challenging Thomson’s
model
• Shot positive particles through a thin sheet of gold foil.
• Predicted: Most particles would pass straight through the foil and some particles would
bend (deflect) slightly.
Chapter 3-Elements and the Periodic Table
• Observed: Most particles passed straight through the foil with little or no deflection and a
FEW particles were deflected at a very LARGE angle.
• Conclusion: The atom is mostly empty space BUT has a positive charge at the center.
- Nucleus: Positive center of an atom.
- Protons: Positively charged particles in atom’s nucleus.
Bohr’s Planetary Model
• 1913 - Rutherford’s student - Niels Bohr - Revised Rutherford’s Model
• Said that electrons are found only in specific orbits around the nucleus.
• Like planets orbiting the sun.
• Electrons have a fixed energy.
Cloud Model
• 1920s - Electrons do not orbit the nucleus like planets.
• Move around the nucleus in a cloud-like region.
• Electron movement related to the energy level: specific amount of energy an electron has.
Chapter 3-Elements and the Periodic Table
Modern Atomic Model
• 1932 - James Chadwick - Found another particle
• Neutron: particle with no electric charge found in
the nucleus of an atom.
• Center of an atom = protons and neutrons
• Cloudlike region = moving electrons
** Protons and electrons balance charge, NOT MASS!
** Proton Mass = Neutron Mass (Make up most of
atom’s mass)
• Atomic Mass Unit (AMU) = the mass of 1 proton/neutron
Atomic Number: The # of protons in the nucleus of an atom
- Unique to each element
- All elements of the same element have the same # of protons.
- Example: Carbon = 6 protons = atomic # 6
Isotopes: Atoms with the same number of protons and different numbers of neutrons.
- Identified by mass number: the sum of protons and neutrons in an atom.
Lesson 2: Organizing the Elements
Medeleev’s Discoveries
• 1869 - Dmitri Mendeleev discovered a set of patterns that applied to all the known elements.
• Wrote an element’s melting point, density, color and atomic mass on cards then tried to
organize.
• Noticed appearance of pattern of properties when he arranged elements in order of
increasing atomic mass.
The Periodic Table
• 1st Periodic Table created in 1869.
• Periodic table: an arrangement of elements showing
the repeating pattern of their properties.
• As new elements discovered, periodic table changed.
• Number of protons in nucleus (atomic number),
determines the chemical properties of an element.
• Modern periodic tables are arranged in order of
increasing atomic number.
Chapter 3-Elements and the Periodic Table
Information on the Periodic Table
1) Atomic number: Number of protons in the nucleus
2) Chemical symbol: One or two letter symbols that abbreviate an element’s name.
3) Atomic mass: An average of of an element’s protons and neutrons in all of its isotopes.
Periodic Table Organization
- Periodic table is useful because an element’s properties can be predicted from its location in
the periodic table.
- Periods: Horizontal rows on the periodic table.
- Metals on the left, nonmetals on the right, metalloids in the middle.
- Groups: Vertical columns on the periodic table.
- Elements in each group have similar characteristics.
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Lesson 3: Metals
Metals- elements that are good conductors of electric current and heat.
o Found on the left side of the periodic table.
Properties of Metals
- Physical properties: luster, malleability, ductility,
and conductivity (heat and electrical).
- Reactivity: the ease and speed with which an
element combines, or reacts, with other substances.
- Metals usually react by losing electrons to
other atoms.
- Some metals are very reactive; Na with water
- Corrosion- the deterioration of a metal due to
a chemical reaction in the environment.
- Example: Gold, nickel, iron, sodium
Classifying Metals
-Alkali Metals: Group 1
-Alkaline Earth Metals: Group 2
-Transition Metals: Group 3- 12
-Metals in Mixed Groups: some of the elements in groups 13-16
-Lanthanides and Actinides: Two rows below the main part of the periodic table.
-Transuranium Elements: Elements that follow Uranium on the periodic table
Chapter 3-Elements and the Periodic Table
Lesson 4: Nonmetals and Metalloids
Nonmetals- an element that lacks most of the properties of a metal..
o Found on the right side of the periodic table (except Hydrogen!!)
Physical Properties of Nonmetals
- Poor conductors of electric current and heat.
- Solids tend to be dull and brittle.
- Lower densities than metals.
- Many are gases at room temperature.
Chemical Properties of Nonmetals
Nonmetals usually react by losing electrons to
other atoms.
- When nonmetals react, electrons move from the metal atoms to the nonmetal atoms.
- Many nonmetals can form compounds with other nonmetals. In these compounds, atoms share
their electrons to form bonds.
- Example: Carbon, Nitrogen, Silicon, Germanium, Neon
Lesson 5: Radioactive Elements
Radioactive Elements: Elements that go through the process
of radioactive decay.
- Radioactive decay: the atomic nuclei of radioactive
isotopes release fast-moving particles and energy.
- Example of a nuclear reaction: process that involves
the particles of an atom’s nucleus.
- Radioactivity: The spontaneous emission of radiation by an
unstable atomic nucleus.
-depends on stability of an atom’s nucleià difference in # of protons and neutrons.
Radiation- rays and particles that are emitted by radioactive elements.
- Uses of radioactive isotopes:
1) Radioactive dating
2) Tracers
3) Medicine
4) Nuclear Energy