ChemH Unit 2: Matter and the Atom Study Guide

Comprehensive vocabulary flashcards covering key terms, atomic discoveries, scientists, and radioactivity concepts from Unit 2: Matter and the Atom.

Matter

Anything that has mass and takes up space.

Pure Substance

Matter that has a uniform and definite composition, consisting of either a single element or a single compound.

Mixture

A physical blend of two or more substances that are not chemically combined.

Element

The simplest form of matter that has a unique set of properties and cannot be broken down into simpler substances by chemical means.

Compound

A substance containing two or more elements chemically combined in a fixed proportion.

Heterogeneous mixture

A mixture in which the composition is not uniform throughout and the individual components remain distinct.

Homogeneous mixture

A mixture in which the composition is completely uniform throughout, also known as a solution.

Solution

A homogeneous mixture of two or more substances, typically composed of a solute dissolved in a solvent.

Physical property

A quality or condition of a substance that can be observed or measured without altering the substance's chemical identity or composition.

Physical change

A change during which some properties of a material alter, but the chemical composition of the material remains identical.

Chemical property

The ability of a substance to undergo a specific chemical change or react to form new substances.

Chemical change

A change that produces matter with a different chemical composition than that of the original matter.

Chemical reaction

A process in which one or more starting substances (reactants) are converted into one or more new substances (products).

Reactant

A starting substance present at the beginning of a chemical reaction.

Product

A new substance formed as a result of a chemical reaction.

Law of Conservation of Mass

A fundamental law stating that in any physical change or chemical reaction, mass is neither created nor destroyed; total mass of reactants equals total mass of products.

Atom

The smallest unit or particle of an element that retains the chemical identity and properties of that element.

Proton

A positively charged subatomic particle found in the nucleus of an atom, with a relative mass of approximately $1\,\text{amu}$.

Neutron

A neutral subatomic particle having no electrical charge, located within the nucleus, with a relative mass of approximately $1\,\text{amu}$.

Electron

A negatively charged subatomic particle with very little mass that occupies the space outside the atomic nucleus.

Ion

An atom or group of bonded atoms that possesses a net positive or negative electrical charge due to the loss or gain of one or more electrons.

Isotope

Atoms of the same element that contain identical numbers of protons but differing numbers of neutrons, resulting in different mass numbers.

Cathode ray tube

An evacuated glass tube used by J.J. Thomson to produce a stream of negatively charged particles, leading to the discovery of the electron.

Gold foil experiment

An experiment conducted by Ernest Rutherford where alpha particles were fired at thin gold foil; the deflection of particles proved the existence of a small, dense, positively charged nucleus.

Democritus

The ancient Greek philosopher who first proposed that matter is composed of tiny, indivisible, and indestructible particles called atomos.

John Dalton

The English chemist who formulated the first modern atomic theory consisting of 4 postulates explaining the nature and chemical combination of atoms.

J.J. Thomson

The scientist who discovered the electron using the cathode ray tube and proposed the plum pudding atomic model.

Ernest Rutherford

The scientist who discovered the atomic nucleus through the gold foil experiment and proposed the nuclear model of the atom.

Niels Bohr

The scientist who proposed the planetary atomic model where electrons travel only in specific circular orbits or fixed energy levels around the nucleus.

Erwin Schrödinger

The physicist who formulated the quantum mechanical model of the atom, treating electrons as wave-like entities inside three-dimensional probability regions called orbitals.

James Chadwick

The English physicist who experimentally confirmed the existence of the neutron in the nucleus of an atom.

Radioactivity

The spontaneous process by which an unstable atomic nucleus releases energy and matter by emitting radiation.

Radiation

The penetrating particles and electromagnetic rays emitted by a radioactive source.

Radioactive decay

The spontaneous breakdown of an unstable atomic nucleus resulting in the release of particles and energy until stability is achieved.

Nuclear radiation

Rays and particles, including alpha particles, beta particles, and gamma rays, emitted from an atomic nucleus during radioactive decay.

Alpha decay

A radioactive decay process where an unstable nucleus emits an alpha particle ($^4_2\text{He}$), reducing the mass number by 4 and the atomic number by 2.

Beta decay

A radioactive decay process where a neutron in an unstable nucleus converts into a proton while emitting a high-speed electron ($^0_{-1}\beta$ or $^0_{-1}e$), raising the atomic number by 1.

Gamma rays

High-energy electromagnetic radiation ($^0_0\gamma$) emitted from an unstable nucleus that possesses no mass and no electrical charge.

Radioisotope

An unstable isotope of an element that undergoes spontaneous nuclear decay and emits ionizing radiation.

Transmutation

The conversion of an atom of one chemical element into an atom of a different element via radioactive decay or nuclear bombardment.

Half life

The duration of time required for half of the radioactive nuclei in a given sample of a radioisotope to decay.

Decay series

A sequential series of radioactive decays that an unstable parent radioisotope undergoes until reaching a stable, non-radioactive end product.