AP Biology Chapter 2

Vocabulary flashcards generated from AP Biology Chapter 2 lecture notes covering elements, atomic structure, subatomic particles, chemical bonding, and reaction equilibrium.

Matter

Anything that has mass and takes up space.

Element

A substance that cannot be broken down by chemical reactions.

Compound

A substance consisting of two or more elements in a fixed ratio that possesses emergent properties, such as $NaCl$.

Essential Elements

Atoms an organism needs to survive and reproduce, where Carbon, Hydrogen, Oxygen, and Nitrogen make up about $96\%$ of living matter.

Trace Elements

Elements required by an organism in minute quantities, such as iodine for thyroid function or iron for hemoglobin.

Valence Electrons

The number of electrons located in an atom's outermost shell.

Valence Shell

The outermost electron shell of an atom.

Atom

The smallest unit of matter that retains emergent properties.

Proton

A basic building block of matter located in the nucleus with a positive electrical charge that decides the chemical element of an atom.

Neutron

A subatomic particle located in the nucleus next to protons that determines isotope stability and keeps the atom's center functioning.

Electron

A subatomic particle occupying electron shells with a negative electrical charge that is tinier than protons and neutrons and determines chemical reactivity.

Isotope

Different atomic forms of the same chemical element.

Radioactive Isotopes

Isotopes that decay spontaneously and are used as biological tracers in experiments, such as tracking metabolic pathways.

Potential Energy

The energy that matter possesses because of its location and structure.

Half-life

The fixed rate at which a radioactive isotope decays into another isotope or element.

Electron Shells

Energy levels outside the atom's nucleus where electrons reside.

Atomic Number

The number of protons in an atom, which also equals the number of electrons in a neutral atom.

Mass Number

The total number of protons and neutrons in an atom's nucleus.

Radiometric Dating

A process measuring the ratio of isotopes to determine the number of years since an organism was fossilized.

Covalent Bond

A strong bond in when two atoms share a pair of valence electrons.

Nonpolar Covalent Bond

A covalent bond with equal sharing of electrons, such as in $O_2$ or C-H bonds.

Polar Covalent Bond

A covalent bond featuring unequal sharing of electrons due to differences in electronegativity, creating partial positive and negative charges as in $H_2O$.

Ionic Bond

A chemical bond resulting from the transfer of electrons creating charged ions; weak in water because water molecules hydrate and separate the ions.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Hydrogen Bond

A weak attraction between a partial positive hydrogen atom from a polar covalent bond and an electronegative atom like oxygen or nitrogen.

Van der Waals Interactions

Transient weak attractions driven by asymmetric electron distributions that help stabilize 3D structures of large biological macromolecules.

Reactants

The starting materials that undergo conversion in a chemical reaction.

Products

The resulting materials produced from a chemical reaction.

Chemical Equilibrium

The state in a chemical reaction where the forward reaction rate equals the reverse reaction rate, causing concentrations to stop changing.

Electronegativity

The tendency of an atom to attract electrons when forming chemical bonds.

Electronegativity Scale

A scale that ranks elements based on their electronegativity values, commonly the Pauling scale, which ranges from about 0.7 (for cesium) to 4.0 (for fluorine).

trends in electronegativity

Electronegativity generally increases across a period from left to right and decreases down a group in the periodic table.