Unit 3- Organization of the PT and the Atom- Honors

Element

Made up of only atoms

Democritus

Greek philosopher who coined the term "atom" which means indestructible and indivisible.

Dalton

Re-visited Democritus' ideas about the atom. Stated that all matter is composed of small, indivisible, indestructible particles called atoms and that atoms combine in simple whole number ratios to form atoms.

Thompson

Discovered the first subatomic particle, the electron through the use of a cathode ray tube. Proposed the plum pudding model.

Rutherford

Discovered the existence of a dense, centrally located nucleus filled with a positive charge (proton). Discovered that the atom is mostly empty space. (Gold foil experiment.)

Chadwick

\n Discovered the existence of the neutron.

Bohr

Discovered the Bohr model which stated that electrons exist in distinct orbits or paths around the nucleus. This model only worked for the element hydrogen.

electron cloud model

The current model of the atom. Says that electrons do not exist on specific paths, but are in a cloud that is more dense closer to the nucleus. Also known as the quantum model.

proton

Positively charged particle with a relative mass of 1. Its role is to add mass and stability to an atom. It is used to identify which atom you have.

electron

Negatively charged particle. Its relative mass is 2000 times less than a proton or neutron. Its role is chemical stability.

neutron

Particle with no charge. Its relative mass is 1, which is the same as a proton. Its role is to add stability and mass to an element.

isotope

An atom that has a varying number of neutrons. Every atom is an isotope.

standard nuclear notation

Used to represent each isotope in existance

Millikan

Discovered the mathematical charge of an electron through his oil drop experiment

mass defect

The difference in the mass of the individual nucleons and the mass of the nucleus; the mass that is converted to energy in the formation of the nucleus.

nucleon

A term used to describe the protons and neutrons in an atom.

binding energy

The energy needed to create the nucleus in the formation of an atom. The stronger the binding energy, the more energy it takes to break apart the nucleus.

average atomic mass

\n The weighted mass of all of the naturally occurring isotopes of an atom

alkali metals

most reactive metals on the periodic table. In group I A

alkaline earth metals

reactive metals in group II A of the periodic table

Halogens

Most reactive non-metal group. Found in group VII A

Noble Gases

Least reactive elements on the table. Found in group VIII A

valence electrons

Electrons on the outermost energy level of an atom; a number between 1 and 8; denoted by the roman numerals of the A groups

Metalloids

Elements that have properties of both metals and nonmetals. Found along the staircase

Dimitri Mendeleev

Russian scientist that created the periodic table according to increasing atomic mass and similar characteristics

Mosely

re-arranged elements by increasing atomic number

Period

\n A horizontal row of elements in the periodic table

Group

A vertical column in the periodic table. Elements have similar characteristics. Also known as a family

Roman Numerals

Shows the number of valence electrons for the A groups