The Atoms and Molecules

Average Atomic Mass

the weighted average mass of an element's naturally occurring isotopes, calculated by multiplying the mass of each isotope by its relative abundance (as a decimal) and summing the results.

Isotope

atoms of the same element that have the same number of protons but different numbers of neutrons, leading to different atomic masses

Electron

A negatively charged particle that is found in the electron cloud and was discovered by J.J Thompson.

Proton

A positive particle that is found in the nucleus and discovered by Ernest Rutherford 

Neutron

A neutral particle that is found in the nucleus discovered by James Chadwick 

Nucleus

A positively charged center of an atom made up of protons and neutrons. Discovered by Rutherford

Atomic Number

The number of protons in the nucleus

Mass Number

The total count of protons and neutrons in the nucleus.

Law of Conservation of Mass

A law that states no matter can be created nor destroyed. Created by Lavoisier

What is the charge of an atom

Neutral

What is the smallest subatomic particle?

Electron

What is the largest part of an atom?

Area around the nucleus

What determines atomic mass

The protons and neutrons

What particles effect charge

Electrons and Protons

What particles effect identity 

Protons 

What particles effect mass 

Protons and Neutrons 

Why do you balance equations?

The law of conservation of mass

To calculate Molar Mass

Multiply Molar mass of given sub atomic particles than add 

H2O 

H: 1.008(2)

O: 15.999

= 18.015

particle to mole

8.30 × 10²² molecules 

Divide by Avogadros

6.022 × 10²³ 

mole to particle

4.00 moles 

Multiply by Avogadros

mass to mole

Divide by Molar mass

mole to mass

Multiply by Molar mass

mass to particle

Divide by Molar mass

Multiply by Avogadros

particle to mass

Divide by avogadro

Multiply by molar mass 

Democritus 

First to say that something can only be divided so many times (Atomus)

400 BCE

Solid Sphere Model

Dalton

Created the first formal atomic theory based off of Lavoisier and Prosts’ ideas 

Circa 1808

Thomson

Used the Cathode Ray tube experiment

Discovered electrons 

Circa 1897

Plum pudding model (First to show subatomic particles) 

Millikan

Oil drop experiment

Determined that mass of an electron 

Circa 1909

Rutherford

Discovered the nucleus/ protons

Gold foil experiment 

Model used is the subatomic/ nucleus model 

Circa 1911 

Chadwick

Discovered the neutron 

Circa 1932

Aristotle

Believed that things could be divided infinitely

Believe in the basic elements made up everything 

330 BCE 

Dalton’s first atomic theory

1: Each element consists of indivisible, minute particles (atoms)

2: Atoms can be neither created nor destroyed in a Chemical reaction 

3: All atoms of a given element are identical 

4: Atoms chemically combined in definite whole number ratios

5: Atoms of different elements have different masses

Which of Dalton’s postulates are no longer true?

Postulate 1 and 3

1: Subatomic particles (protons, electrons, neutrons 

3: Isotopes 

What is the order of these discoveries

Aristotle, Democritus, Dalton, Thomson, Millikan, Rutherford, Chadwick

ADDTMRC

Gold foil Experiment

Used by Rutherford to discover the nucleus and Protons. He blasted a sheet of gold foil with positively charged alpha particles. When the particles got near the nucleus they would warp around.

Cathode Ray Tube experiment

Used by JJ Thompson to discover electrons

Involved a glass tube with a vacuum inside, where a high voltage was applied to two metal electrodes, a cathode (negative) and an anode (positive). This created a glowing, invisible "cathode ray" that traveled from the cathode to the anode. By placing a positive plate nearby, the ray was deflected, proving it consisted of negatively charged particles, which were the first discovered electrons.

Oil Drop Experiment

Used by Robert Millikan to discover the mass of an electron

Balancing the gravitational force on tiny oil droplets with an upward electric force from charged parallel plates.