Unit 2: Atomic Theory, Periodic Table, Light and Energy, and Chemical Bonding

Comprehensive practice flashcards covering the historical development of atomic theory, subatomic particles, periodic table trends, quantum mechanics of light and electron orbitals, types of chemical bonding, and intermolecular forces.

Dalton's Atomic Theory

A theory proposed in 1803 by John Dalton stating that all matter is composed of tiny indivisible particles called atoms, all atoms of a given element are identical, atoms of different elements differ in mass, and atoms combine in simple whole-number ratios to form compounds.

Cathode Rays

Streams of negatively charged particles (electrons) identified by J. J. Thomson in 1897 using electric and magnetic fields, demonstrating that atoms contain internal subatomic particles.

Rutherford's Gold Foil Experiment

An experiment directed by Ernest Rutherford where positively charged alpha ($\alpha$) particles were aimed at a thin gold foil; the deflection of a small fraction of particles revealed that the atom's positive charge and nearly all of its mass reside in a tiny, dense center.

Nucleus

The extremely small, dense center of an atom containing all of its positive charge and nearly all of its mass, surrounded by a large volume of mostly empty space populated thinly by electrons.

Electron ($\text{e}^-$)

A subatomic particle discovered by J. J. Thomson in 1897 located outside the nucleus, having a $-1$ relative charge, an absolute mass of $9.11 \times 10^{-28}\,\text{g}$, and a relative mass of approximately $0\,\text{amu}$ ($0.000549\,\text{amu}$).

Proton ($\text{p}^+$)

A positively charged subatomic particle discovered by Rutherford in 1919 located inside the nucleus, having a $+1$ relative charge, an absolute mass of $1.673 \times 10^{-24}\,\text{g}$, and a mass of approximately $1\,\text{amu}$ ($1.00728\,\text{amu}$).

Neutron ($\text{n}^0$)

An uncharged subatomic particle discovered by James Chadwick in 1932 located inside the nucleus, having a neutral charge ($0$), an absolute mass of $1.675 \times 10^{-24}\,\text{g}$, and a mass of approximately $1\,\text{amu}$ ($1.00867\,\text{amu}$).

Atomic Mass Unit (amu)

A standard unit of mass defined as exactly $\frac{1}{12}$ the mass of a single carbon-12 atom, equal to $1.6606 \times 10^{-24}\,\text{g}$ and abbreviated as "$\text{u}$".

Atomic Number ($Z$)

The total number of protons in the nucleus of an atom, which uniquely determines the element's chemical identity; in a neutral atom, it is also equal to the number of electrons.

Mass Number ($A$)

The total sum of protons and neutrons in the nucleus of an atom ($A = \#\text{p}^+ + \#\text{n}^0$).

Nuclide Symbol

A standard chemical representation written as $^A_Z X$, where $X$ is the element symbol, $A$ is the mass number, and $Z$ is the atomic number.

Isotopes

Atoms of the same chemical element that have the same number of protons (same atomic number $Z$) but different numbers of neutrons (different mass number $A$).

Average Atomic Mass

The weighted average of the atomic masses of an element's naturally occurring isotopes, calculated by multiplying each isotope's mass in amu by its fractional abundance and summing the results.

Period

A horizontal row of elements on the periodic table across which elements demonstrate recurring periodic properties and trends.

Group (Chemical Family)

A vertical column of elements on the periodic table that share identical numbers of valence electrons and similar chemical properties.

Representative Elements

The main-group chemical elements found in the "A" groups (Columns 1A through 8A) of the periodic table.

Transition Elements

The metallic elements located in the "B" groups (10 columns spanning 3B through 2B) of the periodic table, characterized by the filling of $d$ subshells.

Lanthanides

The series of inner-transition elements comprising atomic numbers $58$ through $71$ displayed in the upper detached strip at the bottom of the periodic table.

Actinides

The series of inner-transition elements comprising atomic numbers $90$ through $103$ displayed in the lower detached strip at the bottom of the periodic table.

Alkali Metals

The soft, highly reactive metallic elements belonging to Group 1A of the periodic table with an $ns^1$ valence electron configuration.

Alkaline Earth Metals

The metallic elements belonging to Group 2A of the periodic table possessing an $ns^2$ valence electron configuration.

Halogens

The reactive nonmetal elements belonging to Group 7A of the periodic table possessing an $ns^2 np^5$ valence electron configuration.

Noble Gases

The chemically stable and unreactive nonmetal gases found in Group 8A of the periodic table having a complete octet with an $ns^2 np^6$ valence electron configuration.

Metals

Elements that display a metallic luster, are malleable and ductile, conduct heat and electricity efficiently, and exist as solids at room temperature (with the exception of mercury).

Nonmetals

Elements that lack luster, are brittle and poor conductors of heat and electricity, and exist in various physical states (solid, liquid, or gas) at room temperature.

Metalloids

Elements along the dividing line (including B, Si, Ge, As, Sb, Te, and At) that exhibit properties intermediate between metals and nonmetals and act as semiconductors.

Photoelectric Effect

The phenomenon explained by Albert Einstein in which light shining on a metal ejects electrons, demonstrating that light exhibits particle-like properties alongside wave behavior.

Wave-Particle Duality

The quantum physical principle that light and subatomic particles (such as electrons) simultaneously exhibit the characteristics of both waves and particles.

Wavelength ($\lambda$)

The linear distance between two consecutive identical points (such as crests or troughs) on a continuous wave.

Frequency ($\nu$)

The number of wave cycles that pass a fixed reference point per second, which is inversely related to wavelength according to the equation $c = \lambda \nu$.

Planck's Constant ($h$)

The fundamental constant of proportionality relating the energy of a photon to its frequency ($E = h\nu$), equal to $6.626 \times 10^{-34}\,\text{J}\cdot\text{s}$.

Quantized

A physical condition where energy or other physical properties are restricted to specific, discrete values rather than varying continuously.

Bohr Model

A model of the hydrogen atom proposed by Niels Bohr where electrons orbit the nucleus only in discrete, quantized circular paths corresponding to specific energy levels ($n = 1, 2, 3\dots$).

Atomic Orbital

A three-dimensional probability map derived from Schrödinger's wave equation ($\Psi^2$) indicating a region in space with a high probability of finding an electron.

Principal Energy Level ($n$)

The main energy shell of an atom designated by the principal quantum number $n$ ($n = 1, 2, 3\dots\infty$); as $n$ increases, both the electron's energy and average distance from the nucleus increase.

Pauli Exclusion Principle

A quantum mechanical rule stating that an atomic orbital can hold a maximum of 2 electrons, which must have opposite spins.

Ground State

The lowest possible energy state and most stable electron configuration of an atom.

Excited State

An unstable, higher energy state of an atom occurring when an electron absorbs energy and transitions to an orbital beyond its lowest available energy level.

Valence Electrons

The electrons located in the outermost principal energy level ($s$ and $p$ subshells) of an atom, reaching a maximum of 8, that determine chemical bonding and reactivity.

Isoelectronic

Atoms and ions that share identical numbers of electrons and the exact same electron configuration (such as $\text{Na}^+$ and $\text{O}^{2-}$).

Ionic Bond

A chemical bond formed by the transfer of valence electrons from a metal to a nonmetal, generating oppositely charged ions held together by strong electrostatic crystalline forces.

Covalent Bond

A chemical bond formed by the sharing of one or more electron pairs between two nonmetal or metalloid nuclei.

Electronegativity

The relative ability of an atom within a covalent bond to attract shared electron pairs toward itself, increasing across a period and decreasing down a group (Fluorine is highest at $4.0$, Francium lowest at $0.7$).

Nonpolar Covalent Bond

A covalent bond with an equal sharing of bonding electrons and a symmetrical electron cloud, typically occurring when the electronegativity difference is less than or equal to $0.4$.

Polar Covalent Bond

A covalent bond characterized by an unequal sharing and unsymmetrical distribution of bonding electrons, occurring when the electronegativity difference is between $0.4$ and $1.9$.

Dipole-Dipole Force

An attractive intermolecular force between polar molecules resulting from the electrostatic attraction between permanent partial positive ($\delta^+$) and partial negative ($\delta^-$) ends.

London Dispersion Forces

Weak, temporary intermolecular attractive forces present in all atoms and molecules that result from momentary fluctuations in electron distribution inducing temporary dipoles in adjacent particles.

Hydrogen Bonding

An unusually strong dipole-dipole attraction occurring when hydrogen is covalently bonded directly to a highly electronegative atom ($\text{N}$, $\text{O}$, or $\text{F}$) and interacts with an electronegative atom on a neighbor.

Capillarity of Water

The ability of water to move upward against gravitational forces through narrow spaces, such as plant vessels, driven by surface tension and hydrogen bonding interactions.

Density Anomaly of Water

The unique physical property where solid water (ice) is less dense than liquid water because each water molecule forms four open, hexagonal hydrogen bonds that trap air and increase overall volume.

H

Hydrogen

He

Helium

Li

Lithium

Be

Berylium

B

Boron

C

Carbon

N

Nitrogen

O

Oxygen

F

Flourine

Ne

Neon

Na

Sodium

Mg

Magnesium

Al

Aluminum

Si

Silicon

P

Phosphorus

S

Sulfur

Cl

Chlorine

Ar

Argon

K

Potassium

Ca

Calcium

Sc

Scandium

Ti

Titanium

V

Vanadium

Cr

Chromium

Mn

Manganese

Fe

Iron

Co

Cobalt

Ni

Nickel

Cu

Copper

Zn

Zinc

Br

Bromine

Kr

Krypton

Rb

Rubidium

Sr

Stronium

Pd

Palladium

Ag

Silver

Cd

Cadmium

Sn

Tin

I

Iodine

Xe

Xenon

Cs

Cesium

Ba

Barium

Pt

Platinum

Au

Gold

Hg

Mercury

Pb

Lead

Rn

Radon