Chapter 2: Atoms, Molecules, and Ions (Video Notes)

Vocabulary flashcards covering key terms from the lecture notes on atomic theory, isotopes, the periodic table, and chemical nomenclature.

Atom

The basic unit of an element that can enter chemical bonds; in Dalton's view it was indivisible, later found to have internal structure.

Dalton's atomic theory

Elements consist of tiny particles called atoms; all atoms of an element are identical; compounds are formed from atoms of different elements; chemical reactions rearrange atoms, not create or destroy them.

Element

A pure substance made of only one type of atom.

Compound

A substance formed when atoms of two or more elements combine in fixed ratios.

Law of constant composition

The relative kinds and numbers of atoms in a given compound are constant.

Law of multiple proportions

When two elements form more than one compound, a fixed mass of one element combines with small whole-number ratios of the other.

Subatomic particles

The particles that make up atoms: electrons, protons, and neutrons.

Electron

A negatively charged subatomic particle that orbits the nucleus.

Cathode ray tube

A glass tube used to study electron beams; electrons travel from the cathode to the anode.

Charge-to-mass ratio (e/m) of the electron

Approximately 1.76 × 10^8 coulombs per gram (C/g).

Millikan's charge of the electron

Determined the electron charge as 1.60 × 10^-19 coulombs.

Mass of the electron

Derived from the e/m ratio and charge; indicates electrons have very small mass.

Radioactivity

Spontaneous emission of radiation by an atom.

Becquerel

Discovered that uranium spontaneously emits high-energy radiation.

Curie

Named radioactivity; discovered polonium and radium.

Radiation

Emission of energy through space as waves or energetic particles.

Nucleus

The very small, dense center of an atom; contains protons and neutrons.

Rutherford's nuclear model

Proposed that atoms have a tiny, dense nucleus with electrons around it; most of the atom is empty space.

Proton

Positively charged subatomic particle located in the nucleus.

Neutron

Electrically neutral subatomic particle located in the nucleus.

Electrons location

Outside the nucleus, in regions around the nucleus.

Atomic number (Z)

The number of protons in the nucleus; identifies the element.

Mass number (A)

The total number of protons and neutrons in the nucleus.

Atomic mass unit (amu)

1 amu = 1.66054 × 10^-24 g; used to express atomic and molecular masses.

Angstrom (Å)

A non-SI unit of length equal to 10^-10 meters, used for atomic scales.

Isotopes

Atoms of the same element that have different numbers of neutrons and thus different masses.

Average atomic mass

The weighted average of an element’s isotopes based on natural abundance.

12C standard

By definition, mass of 12C is exactly 12 amu; 1 g contains 6.02214 × 10^23 amu.

Atomic symbol and atomic number

Elements are represented by one or two-letter symbols; Z is the number of protons.

Atom vs isotope

Isotopes are atoms of the same element (same Z) with different A (mass numbers).

Atomic mass scale and Avogadro's number

1 g contains 6.02214 × 10^23 amu; used to relate grams to atomic masses.

Periodic table

Systematic arrangement of elements by increasing atomic number and recurring properties.

Periods

Horizontal rows on the periodic table.

Groups

Vertical columns on the periodic table; elements in a group have similar properties.

Alkali metals

Group 1A elements; highly reactive metals: Li, Na, K, etc.

Alkaline earth metals

Group 2A elements; Be, Mg, Ca, Sr, Ba, Ra.

Chalcogens

Group 6A elements; O, S, Se, Te, Po.

Halogens

Group 7A elements; F, Cl, Br, I, At.

Noble gases

Group 8A elements; He, Ne, Ar, Kr, Xe, Rn.

Ion

An atom or molecule with a net electric charge due to loss or gain of electrons.

Monoatomic ion

An ion consisting of a single atom (e.g., Na+, Cl-).

Polyatomic ion

An ion composed of two or more atoms (e.g., SO4^2-, NH4+).

Cation

A positively charged ion formed by loss of electrons.

Anion

Negatively charged ion formed by gain of electrons.

Ionic compound

A neutral compound composed of cations and anions held together by ionic bonds.

Writing formulas for ionic compounds

Balance total positive and negative charges; subscripts reflect ion charges; reduce to lowest whole numbers.

Cation naming rules

Metals form cations with names usually equal to the metal; Roman numerals indicate charge when oxidation state varies.

Anion naming rules (monoatomic)

Monoatomic anions end in -ide (e.g., chloride).

Oxyanions naming rules

Polyatomic anions with oxygen end in -ate or -ite.

Hydrogen-containing oxyanions

Oxyanions that gain H+ are named with hydrogen or dihydrogen prefixes.

Common cations list

Examples include H+, Na+, NH4+, Cu2+, Fe3+ (ions derived from common metals).

Common anions list

Examples include F-, Cl-, O2-, NO3-, CO3^2-, SO4^2- (various oxyanions).

Ionic compound naming

Cation name followed by anion name (e.g., CaCl2 = calcium chloride).

Acid nomenclature

Acids contain H+ in water; -ide becomes -ic with hydro- prefix; -ate/-ite become -ic/-ous plus acid.

Binary molecular compounds

Names start with the element on the left; second element ends with -ide; use Greek prefixes to indicate numbers; mono- not used for the first element.

Prefixes for binary compounds

Mono-, Di-, Tri-, Tetra-, Penta-, Hexa-, Hepta-, Octa-, Nona-, Deca-.

Diatomic molecules

Seven elements naturally occur as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2.

Structural vs perspective formulas

Structural formulas show bonding; perspective drawings show three-dimensional arrangement.