Chapter 2: Elements and the Structure of the Atom

Comprehensive vocabulary flashcards covering basic element classifications, atomic structure, isotopes, periodic table organization, and valence electrons based on the Chapter 2 lecture notes.

Element

A pure substance that cannot be broken down into simpler substances by a chemical reaction; each is identified by a one- or two-letter symbol.

Metals

Elements located on the left side of the periodic table which are good conductors of heat and electricity and are shiny solids at room temperature, except for mercury ($Hg$).

Nonmetals

Elements located on the right side of the periodic table that have a dull appearance and are usually poor conductors of heat and electricity.

Metalloids

The seven elements ($B$, $Si$, $Ge$, $As$, $Sb$, $Te$, and $At$) located on the solid line starting at boron that have properties intermediate between metals and nonmetals.

Building-Block Elements

The four elements comprising $96\%$ of the human body mass: oxygen ($O$), carbon ($C$), hydrogen ($H$), and nitrogen ($N$).

Major Minerals

Elements present in smaller amounts in the body requiring at least $100\,mg$ of each in the daily diet, such as Magnesium ($Mg$) and Sulfur ($S$).

Trace Elements

Elements required in the daily diet in amounts usually less than $15\,mg$, such as Iodine ($I$) for proper thyroid function.

Compound

A pure substance formed by chemically combining two or more elements together.

Chemical Formula

A representation consisting of element symbols and subscripts to show the identity and ratio of atoms in a compound.

Subscripts

Numbers in a chemical formula that show the ratio of atoms, such as the $2$ in $H_2O$ indicating two $H$ atoms.

Proton

A subatomic particle located in the nucleus with a charge of $+1$, a mass of $1.6726 \times 10^{-24}\,g$, and an approximate mass of $1\,amu$.

Neutron

A subatomic particle located in the nucleus with a charge of $0$, a mass of $1.6749 \times 10^{-24}\,g$, and an approximate mass of $1\,amu$.

Electron

A subatomic particle located in the electron cloud with a charge of $-1$, a mass of $9.1094 \times 10^{-28}\,g$, and negligible mass in $amu$.

Nucleus

The dense core of the atom containing protons and neutrons where most of the atom's mass is located.

Electron cloud

The region comprising most of the atom’s volume, consisting mostly of empty space where electrons are located.

Atomic number ($Z$)

The number of protons in the nucleus which identifies an element; in a neutral atom, it also equals the number of electrons.

Isotopes

Atoms of the same element that have the same number of protons but a different number of neutrons.

Mass number

The total number of protons plus the number of neutrons for a particular isotope.

Deuterium

An isotope of hydrogen ($H$) consisting of $1$ proton and $1$ neutron.

Tritium

An isotope of hydrogen ($H$) consisting of $1$ proton and $2$ neutrons.

Atomic weight

The weighted average of the masses of the naturally occurring isotopes of an element, reported in atomic mass units ($amu$).

Period

A horizontal row in the periodic table.

Group

A vertical column in the periodic table; elements in the same group have similar chemical properties.

Main group elements

Elements in the tall columns (Groups $1A$ to $8A$) on the right and left sides of the periodic table.

Transition metal elements

Elements located in the $10$ short columns in the middle of the periodic table (Groups $1B$ to $8B$).

Inner transition elements

The lanthanides and actinides located at the bottom of the periodic table which have no assigned group numbers.

Alkali Metals

The elements in Group $1A$ ($Li$, $Na$, $K$, $Rb$, $Cs$, $Fr$) which are soft, shiny, have low melting points, and react with water to form basic solutions.

Alkaline Earth Elements

The Group $2A$ elements ($Be$, $Mg$ , $Ca$, $Sr$, $Ba$, $Ra$) which are shiny solids and less reactive than alkali metals.

Halogens

The Group $7A$ elements ($F$, $Cl$, $Br$, $I$), which are very reactive and exist as diatomic molecules in their elemental form.

Noble Gases

The stable elements in Group $8A$ ($He$, $Ne$, $Ar$, $Kr$, $Xe$, $Rn$) which rarely combine with other elements to form compounds.

Valence Electrons

The electrons in the outermost shell of an atom; for main group elements (except $He$), the number of these electrons equals the group number ($1A$–$8A$).