Terms for Unit 1

Anion

A negatively charged ion. It has gained electrons, having a negative charge.

Fission

A nuclear reaction in which one massive nucleus splits into two smaller nuclei.

Fusion

A nuclear reaction where two smaller nuclei combine to form one big nucleus.

Cation

A positively charged ion. It has lost electrons, therefore having more protons and a positive charge.

Aufbau Principle

A principle stating that an electron will fill in the lowest energy level available, filling into the orbitals outward from the nucleus.

Pauli's Exclusion Principle

A principle stating that no two electrons in the same orbital have the same spin. They will have opposite "spins" represented by arrows going up and down in orbital diagrams.

Groups

Along the period table, the elements are sectioned into special groups and periods along the table, generally based off of their properties. Groups are vertical columns whose atoms have more valence electrons are you go from left to right. There are 18.

Periods

Along the period table, the elements are sectioned into special groups and periods along the table, generally based off of their properties. Periods are the horizontal rows that have atoms with the same amount of electron shells in each row. There are seven.

Electron cloud

Around the nucleus of an atom, there is a region of orbitals that have electrons moving within them. This region is called the electron cloud. It is where there is negative charge.

Electron Configuration

Arrangement/placement of electrons within an atom.

Lewis Dot Diagram

Diagram of the atom with the element symbol and valence electrons around it.

Valence Electron

Electrons found on the outermost orbital/energy level within an electron cloud.

Metals

Elements on the periodic table that have many distinguishing properties such as luster, being solid at room temperature and being good conductors of both heat and electricity. One of the three main classifications of elements.

Metalloids

Elements that contain properties of both metals and nonmetals. They lie on the border/staircase. Most important: Silicon and Germanium.

Gold-Foil Experiment

Ernest Rutherford's experiment whose results showcased that atoms were mostly empty space. In this experiment, he fired positively charged alpha particles at a sheet of gold foil. He found that some deflected and some went through the foil. From this, Ernest Rutherford concluded that a positive charged was concentrated into a center region of the atom.

Transition Metals

Groups 3-12 on the periodic table.

Atomic Radius

Half of the distance between nuclei of two neighboring nuclei. Decreases as you go left to right on the periodic table.

Isotope

In an element, there are variations of atomic mass. This is because some atoms have varying numbers of neutrons. Atoms with a number of neutrons that is not equal to the number of protons are called isotopes.

Nonmetals

In the upper right hand corner of the periodic table. They are brittle, dull solids who do not conduct heat or electricity well.

Billiard Ball Model

John Dalton believed that atoms were hard, spherical, and solid. He saw that these characteristics resembled a billiard (pool) ball, so this atomic model was called the billiard ball model.

Radioactive Decay

Particles of energy are released spontaneously from a radioactive substance. The nucleus will release this energy until it becomes stable again.

Half Life

Radioactive substances all have a half life. This is how long it takes for half of the mass of the substance to decay. When a half life has passed, the radioactive material will be half of its original mass.

Ion

Some atoms will gain or lose electrons to have a full valence shell. The atoms that have an unequal number of protons and electrons are ions. They have varying numbers of electrons.

Electronegativity

The ability of an atom to attract electrons in a bond. Increases going left to right.

Atom

The basic unit/building block of matter. Derived from Greek word "atomos", meaning indivisible (though it is further indivisible into subatomic particles). What everything is made up of.

Nucleus

The center of an atom which is dense and positively charged throughout. Makes up the mass almost entirely.

Ionization Energy

The energy that is exerted to remove an electron from an atom. Increases going left to right on the periodic table (metals usually lose electrons/nonmetals tend to gain)

Alkali Metals

The first group of the periodic table. Extremely reactive metals with one valence electron. They usually form ionic compounds. Properties: Soft, low density, good conductors.

Neutron

The neutral/no charge subatomic particle in the nucleus. Mass of 1 amu.

Proton

The positively charged subatomic particle in the nucleus. Mass of 1 amu.

Alkaline Earth Metals

The second group on the periodic table. Very reactive metals holding two valence electrons. Properties: Silvery colored, soft, and low density.

Plum Pudding Model

This model is an early version of the atomic model that displays an atom as a spherical concentration of positive charge with negative charges (electrons) scattered throughout. The Plum Pudding desert was a popular desert in the time that this atomic model was made, so J.J. Thomson named his model after it.