Atoms, Isotopes, Ions, and Molecules: The Building Blocks

Vocabulary flashcards covering the fundamental concepts of atomic structure, subatomic particles, isotopes, chemical bonding, and reactions from Chapter 2.1.

Matter

Any substance that occupies space and has mass.

Element

A unique form of matter with specific chemical and physical properties that cannot be broken down into smaller substances by ordinary chemical reactions; $92$ of the $118$ known elements occur naturally.

Atom

The smallest component or building block of an element that retains all of the chemical properties of that element.

Nucleus (Atomic)

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

Proton

A positively charged subatomic particle located in the nucleus with an electric charge of $+1$ and a mass of approximately $1.67 \times 10^{-24}\,\text{grams}$ ($1\,\text{amu}$ or Dalton).

Neutron

An uncharged subatomic particle residing in the nucleus of an atom with an electric charge of $0$ and a mass of approximately $1.67 \times 10^{-24}\,\text{grams}$ ($1\,\text{amu}$ or Dalton).

Electron

A subatomic particle that orbits the nucleus with an electric charge of $-1$ and a mass of $9.11 \times 10^{-28}\,\text{grams}$ (about $\frac{1}{1800}\,\text{amu}$).

Atomic Mass Unit (amu)

An arbitrarily defined unit of mass equal to approximately $1.67 \times 10^{-24}\,\text{grams}$ (also called a Dalton), equivalent to the mass of one proton or one neutron.

Atomic Number

The characteristic number of protons inside an element's nucleus, used to distinguish one element from another.

Mass Number

The total number of protons and neutrons in an atom's nucleus, disregarding the negligible mass contribution of electrons.

Isotopes

Different forms of the same chemical element that have the same number of protons but vary in the number of neutrons they possess.

Atomic Mass

The calculated mean of the mass numbers for an element's naturally occurring isotopes, frequently resulting in a fraction (such as $35.45\,\text{amu}$ for chlorine).

Radioactive Isotopes (Radioisotopes)

Unstable isotopes that spontaneously emit neutrons, protons, and electrons to attain a more stable atomic configuration with a lower level of potential energy.

Radioactive Decay

The energy loss that occurs when an unstable atom's nucleus releases radiation, such as carbon-14 losing neutrons to decay into carbon-12.

Beta Decay

The slow radioactive decay process through the emission of electrons or positrons by which carbon-14 ($14\text{C}$) decays gradually into nitrogen-14 ($14\text{N}$).

Half-Life

The time it takes for half of the original concentration of an unstable isotope to decay back to its more stable form (approximately $5{,}730\,\text{years}$ for $14\text{C}$).

Periodic Table

An organizational chart devised by Russian chemist Dmitri Mendeleev in 1869 that displays elements arranged by atomic number in rows and columns based on shared chemical and physical properties.

Chemical Reactivity

The ability of elements to combine and chemically bond with each other, governed by the number and spatial distribution of their electrons.

Molecule

A chemical structure formed when two or more atoms chemically bond together.

Bohr Model

An early model of the atom developed in 1913 by Niels Bohr showing a central nucleus containing protons and neutrons with electrons orbiting in circular energy shells at specific distances.

Octet Rule

The principle stating that, with the exception of the innermost shell, atoms are more stable energetically when they have eight electrons in their valence shell.

Valence Shell

The outermost electron shell of an atom that determines its energetic stability and tendency to form chemical bonds.

Noble Gases (Inert Gases)

Group 18 elements (including helium, neon, and argon) characterized by filled outer electron shells, rendering them non-reactive and highly stable as single atoms.

Electron Orbital

The area or volume of space surrounding the nucleus where an electron is most likely to be found, predicted by quantum mechanical wave functions.

s Subshell

A spherical electron subshell containing one orbital that can hold a maximum of two electrons.

p Subshell

An electron subshell composed of three dumbbell-shaped orbitals oriented in three-dimensional space, capable of holding up to six electrons.

Reactants

The starting substances consumed in a chemical reaction, usually written on the left side of a chemical equation.

Products

The substances formed at the end of a chemical reaction, usually found on the right side of a chemical equation.

Law of Conservation of Matter

The scientific principle stating that under normal circumstances, atoms cannot be created or destroyed, requiring the number of atoms before and after a chemical reaction to be equal.

Compound

A molecule that contains atoms of more than one type of element chemically bonded together.

Equilibrium

A state in a reversible chemical reaction reached when relative balances of reactants and products are maintained as forward and reverse reactions occur at equal rates.

Law of Mass Action

A chemical principle stating that the rate and direction of a reversible reaction are driven by the concentrations of reactants and products (e.g., exhalation of $\text{CO}_2$ driving carbonic acid breakdown).

Cation

A positively charged ion formed when an atom loses one or more negatively charged electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons, designated with an elemental name ending in '-ide'.

Ionic Bond

A chemical bond formed between ions of opposite charges via electrostatic attraction following the transfer of electrons from one atom to another.

Electrolytes

Mineral salts (including sodium, potassium, and calcium ions) necessary in human physiology for nerve impulse conduction, muscle contractions, and water balance.

Covalent Bond

A strong chemical bond formed when atoms share one, two, or three pairs of valence electrons to satisfy the octet rule.

Polar Covalent Bond

A covalent bond wherein electrons are unequally shared between atoms of differing electronegativities, generating slight positive ($\delta+$) and slight negative ($\delta-$) charges.

Nonpolar Covalent Bond

A covalent bond formed between two atoms of the same element or elements with similar electronegativity that share electrons equally without developing partial charges.

Electronegativity

The relative tendency or pull that an atom's nucleus exerts on shared electrons within a chemical bond.

Hydrogen Bond

A weak interaction formed between a slightly positive ($\delta+$) hydrogen atom in a polar covalent bond and a more electronegative atom ($\delta-$) (such as oxygen or nitrogen) in another molecule or region of the same molecule.

Van der Waals Interactions

Weak, distance-dependent attractions between molecules caused by transient, asymmetric fluctuations in electron densities around atoms.