Atom Unit Study Guide - Mid Unit

Atomic Discovery Timeline

Democritus- First atomic theory, stated that everything was made of small particles called ‘atomos’, believed that atoms were INDIVISIBLE

Dalton- Same as Democritus, said that atoms are in ratios and there are different types of atoms for different elements, believed that atoms were INDIVISIBLE

Thomson- Discovered the SUBatomic particle: electron thought that electrons were packed in the positively charged matter, believed that atoms were DIVISIBLE

Rutherford- Discovered that atom was mostly empty space with dense core call the Nucleus inside, Nicleus is positively charged, discovered protons

Bhor- Said that electrons orbit nucleus in shells, specific amount for how many electrons can fit in one shell

Chadwick- Discovered neutrons

+more current models with ‘orbitals’ but these are the basics

MODEL \n

Defenitions

Proton- A subatomic particle that has a positive charge and is found inside the nucleus of an atom. Mass: 1amu

Neutron- A subatomic particle that has no charge and is found inside the nucleus of an atom. Mass: 1amu

Electron- A subatomic particle that has a negative charge and orbits the nucleus of an atom. Mass: 1/1836amu

Valence elctron- Valence electrons are electrons that are located in the outer electron shell of an atom.

Isotope- Each of two or more forms of the same element that contains an equal number of protons but a different number of neutrons. They differ in relative atomic mass but not in chemical properties. Isotopes are written as: (Carbon-14→ 6p+ and 8n)

Ion- A changed atom. Ions can have positive or negative electrical charges based on the number of protons and electrons. Ions are written as: (C²⁺→6p+ and 4e-)