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Unit 3

Chapter Overview
During this unit, students explore elements and isotopes and then calculate average atomic mass. They investigate the development of the modern theory of
the atom, including the historical work of the scientists involved and how the basic structure of the atom was developed. Students also explore how the atomic
structure of each element relates to its placement on the Periodic Table and its various chemical properties.

Main Ideas
The historic scientific discoveries of the nature of the atom have fundamentally changed scientific understanding of the nature of
    *In what ways can analysis of the atom further define our understanding of the chemical and physical properties of matter?
    *How has each historic scientific discovery changed our understanding of the chemical and physical properties of matter and our use of the Periodic Table?
    *In what ways can the Periodic Table be used to demonstrate chemical and physical patterns?

Mathematical relationships exist between properties of light.
    *In what ways can mathematical relationships between properties of light be demonstrated?

***Students may think electrons orbit the nucleus of an atom in a plane similar to planets orbiting the Sun, rather than understanding the electron cloud model.
***Students may think atoms disappear during a physical or chemical change rather than being conserved.
***Students may think atoms have properties just like their elements.
***Students may think atoms “want” to gain, share, or lose electrons, rather than understanding that chemical bonds result in more stable (less reactive) products.
***Students may not understand most elements have isotopes and that not all isotopes are radioactive.
***Students may not understand that the only subatomic particles important in understanding the Periodic Table and bonding are electrons, protons, and neutrons.
***Students may not understand the Periodic Table has not always looked like it does now.
***Students may not understand the important trends within the Periodic Table.
***Students may not understand there is more than one model of the atom.

Periodic Table – a table of the chemical elements arranged in order of atomic number
Chemical Family – column of elements in the periodic table with similar chemical properties, also called group, there are 18
Alkali Metals – group 1 of the periodic table, very reactive metals
Alkaline Earth Metals – group 2 of the periodic table, easily reactive metals, only found in compounds in nature
Transition Metals – groups 4-12 in the periodic table, metallic elements
Halogens – group 17 in the periodic table, reactive nonmetals
Noble Gasses – group 18 of the periodic table, nonreactive gasses
Bohr Atom – the simplest picture of the structure of the atom, electrons orbit around the nucleus
Dalton’s Postulates – theory with five parts that explain matter in terms of atoms and their properties
Atom – smallest component of an element, shares the chemical properties of the element
Protons – subatomic particle found in the nucleus, positive charge
Neutrons – subatomic particle found in the nucleus, has no charge
Nucleus – central part of the atom, contains protons and neutrons
Electrons – smallest particle of the atom, negative charge
Valence Electrons – those electrons involved in the formation of chemical bonds
Atomic Number – number of protons in the nucleus of an atom, determines its place on the periodic table
Mass Number – total number of protons and neutrons in an atomic nucleus
Average Atomic Mass – sum of the masses of an element’s isotopes multiplied by its natural abundance
Atomic Radius – a measure of the size of an atom of an element from the nucleus to the outer electrons
Ionic Radius – a measure of the size of an ion of an element in a crystal (usually measured by taking half the distance between two nuclei)
Isotopes – atoms of an element that have the same atomic number (protons) but different mass numbers due to different numbers of neutrons in their nuclei
Hyphen Notation – a way of designating the isotopes of an element using its name (or symbol), a hyphen, and the mass number (ex: uranium-238)
Ionization Energy – a chemical property that describes the amount of energy required to remove an electron from an atom
Electron Affinity – amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion
Oxidation Numbers – number assigned to an element in chemical combination that represents the number of electrons lost (or gained, if the number is negative) by an 
atom of that element in the compound
Electronegativity – a chemical property that describes the extent to which an atom attracts electrons towards itself; cannot be directly measured
Atomic Emission Spectrum – the variety of frequencies of electromagnetic radiation (light) seen through a spectroscope that are emitted by electrons as they transition from higher to lower energy levels; unique for each element
Electromagnetic Spectrum – all of the frequencies of electromagnetic radiation or light
Frequency – the number of cycles of an event per unit time; one Hertz (Hz) means one cycle per second
Planck’s Constant – a constant value that relates the energy of a photon of light to its frequency
Wavelength – the length between successive peaks (or troughs) of a wave
Spectroscope – instrument used to analyze the component parts of a sample by separating its parts into a spectrum


Other Valuable Resources

History of the Atom: Crash Course

History of the Atom: Bozeman Science

Periodic Table: Bozeman Science

Atomic Nucleus: Crash Course

Atoms and the PT: Bozeman

Periodic Trends