Atomic Structure and Matter Classification

Flashcards covering key vocabulary from the lecture on Atomic Structure and Matter Classification, including states of matter, matter composition, scientific method terminology, atomic laws, atomic structure, and the mole concept.

Matter

Anything with mass and occupying space; consists of atoms and molecules in motion. The physical universe is entirely comprised of matter and energy.

Atoms

Submicroscopic particles, building blocks of elements and molecules. Each atom has a unique identity based on its atomic number.

Molecules

Two or more atoms combined through chemical bonds, forming a discrete unit.

Solid

A state of matter that possesses a fixed volume and rigid shape. Particles are tightly packed in a fixed, ordered arrangement, vibrating in place, representing the most ordered state of matter.

Liquid

A state of matter that has a distinct volume but takes the shape of its container. Particles are closely spaced but are free to move past one another, allowing liquids to flow.

Gas

A state of matter that has neither a fixed volume nor a fixed shape; it expands to fill its container. Particles are far apart and move randomly and rapidly, representing the least ordered state.

Pure Substances

Matter with distinct properties and a constant composition throughout. They cannot be separated into simpler substances by physical means.

Elements

Fundamental substances that cannot be chemically decomposed into simpler substances. Each element is defined by its atomic number (number of protons).

Compounds

Substances formed when two or more different elements are chemically combined in fixed, definite proportions. Their properties are distinct from those of their constituent elements.

Mixtures

Combinations of two or more pure substances that are physically mixed but not chemically combined. Their proportions can vary, and they retain the properties of their components.

Homogeneous Mixture (Solution)

Mixtures with a uniform composition and appearance throughout. All parts of the mixture are identical.

Heterogeneous Mixture

Mixtures where the composition is not uniform; different regions have different properties or appearances. Components are visibly distinguishable.

Intrinsic Properties

Properties of matter that are independent of the amount of substance present (e.g., density, melting point, boiling point, color).

Extrinsic Properties

Properties of matter that are dependent on the amount of substance present (e.g., mass, volume, length).

Empirical

Based on observation and experimentation.

Observation

A phenomenon competent observers agree upon, often quantitative measurements.

Scientific Law

A general statement about natural quantities, tested and uncontradicted, describing what happens but not why.

Hypothesis

An initial attempt to explain the underlying cause of an observation; a testable, tentative explanation.

Experiment

A controlled observation designed to test a hypothesis by manipulating variables.

Theory

One or more confirmed hypotheses forming a comprehensive model that explains why natural phenomena occur and predicts behavior. extensively tested and widely accepted.

Law of Conservation of Mass

In any closed system, during a chemical reaction or physical transformation, matter is neither created nor destroyed. The total mass of the reactants must equal the total mass of the products.

Law of Definite Proportions

All samples of a given chemical compound, regardless of their source or method of preparation, contain the same elements in the exact same proportions by mass.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers.

Dalton's Atomic Theory Postulates

Each element is composed of extremely small, indivisible particles called atoms. Atoms of a given element are identical in mass and properties; atoms are neither created nor destroyed in reactions; compounds form when atoms combine in fixed ratios.

Cathode Rays

Experiments with cathode ray tubes (by J.J. Thomson) demonstrated that electricity was transmitted by negatively charged particles, later identified as electrons.

Electron (e-)

A subatomic particle that carries a fundamental negative charge (-1 or -1.60 x 10^-19 C) and has a mass of 9.10 x 10^-28 g. Located in the electron cloud outside the nucleus.

Thomson's "Plum Pudding" Model

A proposed model of the atom where it was a positively charged sphere with negatively charged electrons embedded within it, like plums in a pudding.

Radioactivity

The spontaneous emission by certain elements like Uranium and Radium, revealing that atoms are not indivisible.

Alpha particles (α particles)

A type of radiation that is positively charged (equivalent to a helium nucleus).

Beta particles (β particles)

A type of radiation that is negatively charged (high-energy electrons).

Gamma rays (γ rays)

A type of radiation that is electromagnetic with no charge or mass.

Rutherford's Gold Foil Experiment

By bombarding thin gold foil with α particles, Rutherford discovered the atomic nucleus, observing that most particles passed through, but some were deflected at large angles.

Nucleus

A tiny, incredibly dense, positively charged center within the atom, discovered by Rutherford.

Proton (p+)

A subatomic particle that carries a fundamental positive charge (+1 or +1.602 x 10^-19 C) and has a mass of approximately 1 atomic mass unit (amu). Located in the nucleus.

Neutron (n0)

A subatomic particle that carries no electrical charge (neutral) and has a mass of approximately 1 amu (slightly heavier than a proton). Located in the nucleus.

Atomic Number (Z)

The characteristic number of protons in the nucleus of an atom. It defines the element and its chemical identity. For a neutral atom, the number of protons equals the number of electrons.

Mass Number (A)

The sum of the number of protons (p+) and neutrons (n0) in an atom's nucleus (A = p+ + n0). This value gives the approximate mass of an atom in atomic mass units (amu).

Isotopes

Atoms of the same element (meaning they have the same atomic number, Z) but possess different numbers of neutrons and therefore different mass numbers (A).

Ions

Atoms that have either lost or gained electrons, resulting in a net electrical charge. The charge (C) is determined by (number of protons - number of electrons).

Cations

Positively charged ions formed when an atom loses one or more electrons.

Anions

Negatively charged ions formed when an atom gains one or more electrons.

Atomic Mass (Weight)

The weighted average of the masses of all naturally occurring isotopes of an element. This is the value commonly found on the periodic table.

Mole (mol)

A fundamental unit in chemistry that provides a bridge between the macroscopic world (grams) and the microscopic world (atoms, molecules). One mole represents a specific number of particles.

Avogadro's Number (NA)

Exactly 6.022 x 10^23 particles (atoms, molecules, ions, or formula units) per mole. This constant allows for conversion between the number of moles and the number of individual particles.

Molar Mass (g/mol)

The mass in grams of one mole of a substance. For elements, it is numerically equal to the average atomic mass of that element in atomic mass units (amu). For compounds, it is the sum of the atomic masses of all atoms in its chemical formula.