Chapter 4: Atoms and Elements

This set of flashcards covers the fundamental concepts of atoms and elements, including chemical symbols, atomic theories, subatomic particle behavior and calculations, isotope notation, and the organization of the periodic table.

Elements

Pure substances from which everything else is built.

Chemical Symbols

One or two letter abbreviations for an element's name, where the second letter is never capitalized.

Dalton's Atomic Theory

A theory developed in 1808 stating that all matter is made of atoms, atoms of an element are identical, atoms combine to form compounds, and chemical reactions involve the rearrangement of atoms.

Atom

The smallest particle of an element.

Law of Conservation of Mass

The principle that mass is neither created nor destroyed during a chemical reaction, meaning the total mass of reactants equals the total mass of products.

Percent Composition

The ratio of the mass of one component to the total mass, expressed as a percentage: $\frac{\text{Mass of One}}{\text{Mass of Total}} \times 100$.

Subatomic Particles

The tiny particles that compose an atom, specifically protons, neutrons, and electrons.

Cathode Rays

Streams of small negatively charged particles called electrons, discovered by J. J. Thomson in 1897.

Plum Pudding Model

A model of the atom proposed by J. J. Thomson where protons and electrons are scattered / distributed throughout the atom.

Gold Foil Experiment

An experiment conducted by Ernest Rutherford in 1911 that led to the discovery of the nucleus and the empty space model of the atom.

Nucleus

The small region in the center of an atom that contains the protons and neutrons and holds a positive charge.

Neutron

A neutral subatomic particle discovered by James Chadwick in 1932 that is located in the nucleus.

Atomic Mass Unit (amu)

A unit of mass defined as the mass of a hydrogen atom with 1 proton; used to compare the mass of all elements to $^{12}C$.

Atomic Number

A number specific to each element that is equal to the number of protons in its nucleus: $\text{Atomic Number} = \text{Number of Protons}$.

Mass Number

The total number of particles in the nucleus of a single atom: \text{Mass Number} = \text{# Protons} + \text{# Neutrons}.

Atomic Symbol

A representation of an isotope that shows the mass number in the upper left, the atomic number in the lower left, and the charge in the upper right of the chemical symbol.

Charge

The electrical state of an atom determined by the difference between protons and electrons: \text{Charge} = \text{# Protons} - \text{# Electrons}.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different mass numbers.

Atomic Mass

The weighted average of all naturally occurring isotopes of an element, listed below the symbol on the periodic table.

Periodic Table

An arrangement of elements created by Dmitri Mendeleev in 1872, originally organized by increasing atomic mass and similar properties.

Groups

Vertical columns on the periodic table that contain elements with similar properties.

Periods

Horizontal rows of elements on the periodic table.

Alkali Metals

Elements in Group 1A (1), including Li, Na, K, Rb, Cs, and Fr, but excluding Hydrogen.

Alkaline Earth Metals

Elements in Group 2A (2), including Be, Mg, Ca, Sr, Ba, and Ra.

Halogens

Elements in Group 7A (17), including F, Cl, Br, I, and At.

Noble Gases

Elements in Group 8A (18), including He, Ne, Ar, Kr, Xe, and Rn.

Metals

Shiny solids that are ductile, malleable, good conductors of electricity, and have high melting points.

Nonmetals

Elements that are typically not shiny, malleable, or ductile, are poor conductors, and have low melting points and densities.

Metalloids

Elements located along the heavy zigzag line (except Aluminum) that exhibit properties of both metals and nonmetals and act as semiconductors.