Unit 2: Atoms and The Periodic Table

Vocabulary flashcards covering key terms from Unit 2: Atoms and The Periodic Table.

Atom

The smallest unit of an element; the basic unit that retains the properties of that element.

Ion

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

Isotope

Atoms of the same element with different numbers of neutrons.

Atomic Number

The number of protons in the nucleus of an atom.

Atomic Mass

The average mass of all the isotopes of an element.

Chemical Symbol

A one- or two-letter abbreviation for an element.

Electron

A negatively charged particle in an atom.

Electron Cloud

Region around the nucleus where electrons are likely to be found.

Element

A pure substance made of only one kind of atom.

Mass Number

The sum of protons and neutrons in the nucleus.

Nucleus

Center of the atom containing protons and neutrons.

Proton

A positively charged particle in the nucleus.

Neutron

A neutral particle in the nucleus.

Energy Levels (Shells)

Regions around the nucleus that hold electrons.

Bohr Diagram

A diagram showing electrons arranged in shells around the nucleus.

Bohr Model

An atomic model with electrons arranged in energy levels (shells).

Bohr Model 1st energy level (max 2)

First shell can hold up to 2 electrons.

Bohr Model 2nd energy level (max 8)

Second shell can hold up to 8 electrons.

Bohr Model 3rd energy level (max 18)

Third shell can hold up to 18 electrons.

Bohr Model 4th energy level (max 32)

Fourth shell can hold up to 32 electrons.

Compound

A substance formed when two or more elements chemically bond; compounds have properties different from the elements.

Mixture

A combination of two or more substances not chemically bonded; components retain properties and can be separated physically.

Homogeneous Mixture

A mixture with uniform composition and appearance throughout.

Heterogeneous Mixture

A mixture in which the components are visibly distinguishable and can be separated physically.

Group (Periodic Table)

Vertical columns on the periodic table; also called families.

Periodic Table

A chart of the elements showing repeating patterns of properties.

Alkali Metals (Group 1)

Group 1 elements with 1 valence electron; very reactive, soft, silver-colored metals.

Alkaline Earth Metals (Group 2)

Group 2 elements; harder than alkali metals and less reactive.

Halogens (Group 17)

Group 17 nonmetals with 7 valence electrons; highly reactive.

Noble Gases (Group 18)

Group 18 elements with full outer electron shells (8 valence electrons) and high stability.

Valence Electrons

Electrons in the outermost energy level of an atom.

Period

A horizontal row of elements in the periodic table.

Dimitri Mendeleev

Russian scientist who created the periodic table based on atomic mass and left gaps for undiscovered elements.

Henry Moseley

Physicist who arranged the periodic table by atomic number rather than mass.

Reactivity

The ease and speed with which an element combines with other elements or compounds.

Metal

Elements that are good conductors of heat and electricity; usually solid, malleable and ductile.

Nonmetal

Elements that are poor conductors of heat and electricity; can be brittle and exist as solids, liquids, or gases.

Malleable

Capable of being hammered or shaped without breaking.

Ductile

Capable of being drawn into thin wires.

Metalloids

Elements with properties of both metals and nonmetals; often semiconductors.

Semiconductor

A substance that conducts electricity under some conditions.

Anion

Negatively charged ion formed when atoms gain electrons.

Cation

Positively charged ion formed when atoms lose electrons.

Conductivity

The ability of a material to conduct electric current or heat.

Corrosion

The deterioration of metals due to chemical reactions, typically with oxygen and moisture.

Lewis Dot Structure

A diagram showing bonding between atoms and lone pairs of electrons.

Luster

The way a surface reflects light; often associated with metals' shininess.

Matter

Anything that has mass and occupies space; made of atoms and molecules.

Subatomic Particle

The smaller components that make up an atom, including protons, neutrons, and electrons.

Transition Metal

Metals with partially filled d orbitals; conduct electricity, form colorful compounds, and show variable oxidation states.