Chemistry vocab Unit 2 - Atomic Theory, Structure, and Periodic Table

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Atom

The smallest particle of an element that retains all the properties of that element.

Atomic Mass

The weighted average mass of the isotopes of an element.

Atomic Mass Unit

The standard unit that indicates mass on an atomic or molecular scale.

Atomic Number

This is equal to the number of protons in an atom.

Cathode Ray Tube

Used by J.J. Thompson to discover the electron.

Electron

A negatively charged particle with an extremely small mass.

Element

A pure substance that cannot be broken down by physical or chemical means.

Ion

An atom or bonded group of atoms with a positive or negative charge.

Isotope

These are atoms of the same element with the same number of protons but different numbers of neutrons.

Neutron

A neutral subatomic particle in an atom's nucleus.

Proton

A subatomic particle in an atom's nucleus that has a positive charge.

Mass Number

the total number of protons and neutrons in the nucleus of an atom

Alpha Particle

A positively charged particle identical to a helium nucleus that is one of the common types of radioactive emissions.

Electron Cloud

The region of negative charge surrounding an atomic nucleus where electrons are most likely to be found.

Alkali Metals

These are soft, shiny, and silver-colored elements in Group 1, excluding hydrogen.

Physical Properties

Characteristics that can be observed or measured without changing the identity of the substance.

Transition Metals

These are chemical elements in groups 3-12 of the periodic table that has a partially filled d sub-shell, either as a neutral atom or in it common ions.

Halogens

These are chemical elements from Group 17 of the periodic table that react with metals to form salts.

Alkaline Earth Metals

These are shiny, silvery-white, and reactive metals in group 2 on the periodic table that easily form basic, alkaline solutions when mixed with water.

Chemical Properties

This is characteristic of a substance that can only be observed or measured when it changes into a different substance.

Ductile

A substance can be stretched into a thin wire or pulled into a new shape without breaking.

Non-metals

These are typically gases or dull, brittle solids that are poor conductors of heat and electricity.

Period

A horizontal row of elements in the periodic table

Group

A vertical column of elements in the periodic table; also called a family.

Conductor

This is a material that allows energy—such as electricity or heat—to easily flow through it.

Malleable

A material that can be to be hammered or pressed permanently into thin sheets without breaking or cracking.

Metals

This is a hard, shiny material that is a good conductor of heat and electricity.

Metalloids

This is a chemical element with physical and chemical properties intermediate between metals and nonmetals.

Lanthanides

These are chemical elements with atomic numbers 57 through 71 also known as rare earth metals, and share very similar chemical and physical properties.

Percent Abundance

The percentage amount of all naturally occurring isotopes of an element.

Actinides

These are a series of 15 radioactive, metallic elements in the periodic table, ranging from actinium to lawrencium.

Scientific Law

A statement that describes an observed pattern or action in nature by answering what occurs.

Scientific Theory

A comprehensive explanation of a natural phenomenon that has been rigorously tested and supported by substantial evidence.

Hypothesis

A tentative, testable explanation for a phenomenon in the natural world.

Model

A physical, mathematical, or conceptual representation of a real-world system, object, or process.

Mole

A standard unit of measurement used to count very small particles like atoms, molecules, or ions.

Avogadro’s Number

The exact physical constant of 6.02214076 x 10^23. which represents the number of constituent particles found in exactly one mole of a given substance.