Biology Fundamentals: Atoms, Bonding, and Molecular Properties

Vocabulary flashcards covering atomic structure, periodic properties, chemical bonding (ionic, covalent, hydrogen), electronegativity, polarity, and hydrophilic/hydrophobic characteristics.

Atom

The smallest unit of an element, such as a single oxygen ($O$) atom or carbon ($C$) atom.

Element

A pure substance consisting of only one type of atom, such as oxygen ($O$), hydrogen ($H$), or sodium ($Na$).

Molecule

A particle composed of two or more atoms bonded together, such as $O_2$, $H_2O$, or $CO_2$.

Atomic Number

The number of protons in an atom's nucleus, located at the top of an element's entry on the Periodic Table.

Atomic Mass

The total number of protons and neutrons in an atom, located at the bottom of an element's entry on the Periodic Table.

Nucleus

The central core of an atom that contains protons and neutrons.

Shell Rule ($2-8-8$)

The electron capacity rule for elements in the first three rows of the Periodic Table, where the first shell holds up to $2$ electrons, the second holds up to $8$, and the third holds up to $8$.

Valence Electrons

The electrons located in the outermost electron shell of an atom; a fuller outer shell corresponds to higher stability.

Octet Rule

The rule stating that if an atom does not have $8$ valence electrons, it may gain, lose, or share electrons to fill its outer shell and form chemical bonds.

Electronegativity

A measure of how strongly an atom attracts electrons toward itself in a bond, which increases toward the top right of the Periodic Table.

Ionic Bond

A chemical bond formed between a metal and a nonmetal involving the full transfer of electrons, followed by electrostatic attraction between oppositely charged ions.

Covalent Bond

A chemical bond formed between nonmetals that involves the sharing of electrons.

Nonpolar Covalent Bond

A type of covalent bond where electrons are shared equally between atoms due to equal or similar electronegativity (e.g., $O-O$ or $C-H$).

Polar Covalent Bond

A type of covalent bond where electrons are shared unequally because one atom is more electronegative, resulting in partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

Hydrogen Bond

An attraction between opposite partial charges ($\delta^+$ and $\delta^-$) of separate molecules, such as between adjacent water ($H_2O$) molecules.

Hydrophilic

A term describing polar, water-loving substances that readily interact with water, often containing oxygen ($O$) and nitrogen ($N$) atoms.

Hydrophobic

A term describing nonpolar, water-fearing substances that do not interact well with water, often containing abundant carbon-hydrogen ($C-H$) bonds.