20 terms

Unit 1: Atoms and the Periodic Table

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Physical Property
A characteristic of a substance that can be changed without changing the composition or identity of the substance
Chemical Property
A characteristic of a substance that determines how it will interact with other substances
Atom
The smallest unit of matter (always neutral in charge with the same # of protons and electrons)
Atomic Mass
The average mass of one atom of an element (protons+neutrons)
Atomic Number
The number of protons in an atom (NEVER changes); used to determine an element's identity
Electrical Charge
The positive or negative charge of a subatomic particle
Nucleus
The positively charged center, or core, of an atom containing the protons and nuetrons
Electron Cloud
The area around the nucleus where electrons are found
Energy Levels
Specific regions within the electron cloud where electrons are located, larger atoms = more levels (up to 7)
Subatomic Particles
The 3 small particles that make up an atom
Proton
A positively charged particle located in the nucleus; # NEVER changes; identifies the element
Neutron
A neutral particle (with no electrical charge) located in the nucleus
Electron
A negatively charged particle located in the electron cloud
Valence Electrons
The electrons located in the outermost energy level; determine reactivity
Isotope
An atom with more or less neutrons than the variety shown on the periodic table
Element
A pure substance that cannot be broken down into a simpler substance
Groups/Families
The 18 vertical columns on the Periodic Table
Periodic Table
A chart in which the elements are organized according to their properties
Periods
The 7 horizontal rows on the Periodic Table
Reactivity
The tendency of a substance to undergo a chemical change when exposed to other substances