The Structure of the Atom and the Periodic Table

Comprehensive practice flashcards covering atomic structure, element classification, group characteristics, and periodic trends.

Atom

The basic structural unit of an element and the smallest unit that retains the chemical properties of that element.

Nucleus

A small, dense region containing positively charged protons and uncharged neutrons.

Electrons

Particles with very low mass in contrast to protons and neutrons that populate the diffuse region of negative charge surrounding the nucleus.

Atomic Number (Z)

The number of protons in the nucleus, which determines the identity of an element.

Mass Number (A)

The total number of protons and neutrons in an atom, collectively referred to as nucleons.

Isotopes

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

Ion

A particle formed when an atom loses or gains one or more electrons, resulting in a positive or negative charge.

Cation

A positively charged ion formed when an atom loses an electron.

Anion

A negatively charged ion formed when an atom gains an electron.

Monatomic lon

An ion that contains only one atom, such as $Na^+$ or $Cl^-$.

Polyatomic lon

An ion that contains more than one atom, such as $OH^-$ or $NH_4^+$.

Metals

Shiny substances that are ductile, malleable, solid at room temperature (except mercury), and conduct heat and electricity.

Nonmetals

Poor conductors of heat and electricity that do not have a shiny appearance and can be solids, liquids, or gases at room temperature.

Metalloids

Elements that have properties intermediate between metals and nonmetals.

Building-block Elements

The four gaseous elements ($CHON$) that compose almost $96\%$ of the mass of the human body.

Trace Elements

Elements present in the human body at less than $0.1\%$ by mass, requiring a daily intake of $15\,mg$ or less.

Major Minerals

Minerals present in the human body at $0.1-2\%$ by mass, requiring at least $100\,mg$ in the daily diet.

Mendeleev

The Russian chemist who published the periodic law in $1879$ and arranged elements by atomic mass.

Periodic Law

The principle stating that the properties of elements are a periodic function of their atomic weight.

Period

The horizontal arrangement of elements in the periodic table.

Group (Family)

The vertical columns of elements in the periodic table arranged according to similarities in their properties.

Representative Elements

Elements filling the $s$ and $p$ subshells which belong to subgroup A.

Transition Elements

Elements filling the $d$ and $f$ subshells which belong to subgroup B.

Alkali Metals

Group IA elements (excluding Hydrogen) that have one valence electron, low ionization energies, and a $1+$ charge.

Alkaline Earth Metals

Highly reactive Group IIA elements with two valence electrons that form basic solutions with $pH$ greater than $7$.

Chalcogens

The Group VIA oxygen family, whose name means "ore former."

Halogens

Group VIIA elements that have seven valence electrons and typically exist as diatomic molecules like $F_2$, $Cl_2$, $Br_2$, and $I_2$.

Noble Gases

Chemically stable Group VIIIA elements (also called inert gases) that have eight valence electrons, except for Helium which has two.

Valence Electrons

The outermost electrons in an atom.

Atomic Radius

Calculated as half the distance between two nuclei; it increases from right to left and from top to bottom on the periodic table.

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons; it increases from left to right and bottom to top.

Ionization Energy

The amount of energy required to remove an electron from a neutral atom; it increases from left to right and bottom to top.

Electron Affinity

The amount of energy released when a neutral gaseous atom accepts an electron in its outermost shell.

Metallic Property

A measure of the tendency of an atom to lose electrons; it increases from right to left and from top to bottom.