The Atom

Law of Conservation of Mass

Law of Conservation of Mass

Matter is not created nor destroyed in any ordinary chemical or physical change

Law of Definite Proportions

A chemical compound contains the exact same ​proportions by mass no matter the size of the sample of the compound

Law of Multiple Proportions

If 2 or more different compounds are composed of the same 2 elements, then the ratio of the masses of the 2nd element combined with a certain mass of the 1st element is always a ratio of small whole numbers

Democritus (400 BC)

Named the atom -- 'atomos', meaning small indivisible particle

Dalton ~1803

Concluded that:
All matter is made of atoms
Atoms of a given element are identical in size, mass and properties
Atoms cannot be divided, created or destroyed
Atoms of different elements combine in simple whole# ratios to form compounds
In chemical reactions atoms are combined, separated or rearranged

J.J. Thomson/Millikan

-performed cathode ray tube experiment
-discovered the electron with a mass of less than 1 and a negative charge

Plum Pudding Model

Concluded that electrons ​were negatively charged in a positive cloud

E. Rutherford

Fired alpha particles at gold foil

Positive Nucleus Model

Discovered atom was mostly empty space with
positive center

Modern Atomic Theory

The atom is smallest particle of an element that retains the chemical properties of that element, and could be seperated into subatomic particles

Atomic Number

Symbol; the number of protons in the nucleus of an atom; Identifies each element

Mass Number

the sum of the number of neutrons and protons in an atomic nucleus; Mass# - Atomic# = # of neutrons

12 protons, 12 electrons, 12 neutrons

Find the subatomic particles of Magnesium (Mg)

14 protons, 14 electrons, 14 neutrons

Find the subatomic particles of Silicon (Si)

Isotopes

Atoms of the same element that have different masses; same # of protons and electrons; different # of neutrons

Hyphen Notation

the mass number is written with a hyphen after the name of the element (Ex: Nitrogen-15)

Nuclear Symbol

shows the atomic number, mass number and charge(if any)

Same protons & electrons; 2 neutron difference

State the subatomic particles of Carbon-14 vs Carbon-12

Same protons and neutrons, different electrons

State the subatomic particles of O^2 vs O

Average Atomic Mass

the weighted average of the masses of all naturally occurring isotopes of an element

Turn % into a decimal
Multiply by Mass
Add together

How to calculate atomic weight

2 electron difference, same neutrons and protons

State the Subatomic Particles of O^-2 vs O (^2 is an exponent)