Unit Two Study Guide: Atoms, Atomic Theory, and Introduction to the Periodic Table

Vocabulary study cards reviewing atomic theory, subatomic particles, isotopes, ions, average atomic mass calculations, and periodic table organization based on lecture notes.

Bohr Model

The atomic model created by scientist Niels Bohr.

Aristotle

Ancient philosopher who did not believe in the existence of atoms.

James Chadwick

The scientist responsible for discovering the neutron.

Cathode Ray Tube Experiment

An experiment performed by J.J. Thomson that demonstrated atoms contain negatively charged particles.

Plum Pudding Model

The atomic model created by J.J. Thomson following his discovery of negatively charged particles.

Dalton's Atomic Theory

Theory stating that all matter is made of atoms, atoms of the same element are alike, atoms of different elements are different, atoms are rearranged during chemical reactions, and atoms combine in whole number ratios to form compounds.

Problems with Dalton's Atomic Theory

Two main flaws in Dalton's theory: 1) Atoms can be divided into smaller subatomic particles, and 2) Atoms of the same element are not always identical because of isotopes.

Robert Millikan

Scientist who determined the mass of an electron to be $0.00055\,\text{amu}$.

Proton

A subatomic particle located in the nucleus with a charge of $+1$ that determines the identity of an element.

Neutron

A subatomic particle located in the nucleus of an atom with a charge of $0$.

Electron

A subatomic particle with a charge of $-1$ located outside the nucleus in the electron cloud, contributing the least to the mass of an atom ($0.00055\,\text{amu}$).

Electron Cloud

The region outside the nucleus of an atom where electrons are located.

Atomic Number

The number of protons in an atom, which uniquely identifies the element.

Mass Number

The total number of protons plus neutrons in an atom's nucleus.

Isotope

An atom of the same element that has a different number of neutrons (and mass number), but the same number of protons.

Ion

An atom with a positive or negative overall charge formed because it gained or lost electrons.

Positive Ion

A charged atom formed when an atom loses an electron.

Negative Ion

A charged atom formed when an atom loses a proton (or gains an electron).

Neutral Atom

An atom with no overall charge because it has an equal number of protons and electrons, canceling out the charges.

Period

A horizontal row on the periodic table.

Group or Family

A vertical column on the periodic table.

Metals

Elements located generally on the left side and center of the periodic table.

Nonmetals

Elements located generally on the upper right side of the periodic table.

Metalloid

An element that exhibits some properties of metals and some properties of nonmetals.

Average Atomic Mass

The weighted average mass of an element's naturally occurring isotopes, calculated using the formula $\sum (\text{abundance} \times \text{mass})$.

Radon-222

An atom of radon containing 86 protons, 136 neutrons, and 86 electrons.

Potassium-40 Ion ($+1$ charge)

An ion of potassium containing 19 protons, 21 neutrons, and 18 electrons.

Selenium-79 Ion ($-2$ charge)

An ion of selenium containing 34 protons, 45 neutrons, and 36 electrons.