The AtomCh 3.1

Law of Conservation of Mass◦ Mass cannot be created or destroyed

Law of Definite Proportions◦ Chemical compound always has the same

proportions of elements no matter the size

Law of Multiple Proportions◦ When elements combine, they do so in the ratio

of small whole numbers. The mass of one element combines with a fixed mass of another element 

Foundations of Atomic Theory

1. Matter is composed of atoms

2. Atoms of a given element are identical in mass, size, and properties

3. Atoms cannot be created or destroyed

4. Atoms of different elements combine in simple whole number ratios to form compounds

5. In chemical reactions atoms combine, separate or rearange

Dalton’s Atomic Theory

1. All matter is composed of atoms

2. Atoms of any one element differ in properties from another element

Modern Atomic Theory

The Structure of an Atom

Ch 3.2

Electron- ◦ negatively charged, surround the nucleus

Proton-◦ Positively charged, in nucleus

Neutron-◦ Neutrally charged, in nucleus

Subatomic Particles

Used cathode rays to discover electrons

Found electrons to be negatively charged particles

Plum Pudding Model◦ Negative and

positive charges spread evenly

Thompson

Used alpha particles to discover the nucleus

Rutherford

Composition of Atomic NucleusProtons Neutrons Positive Charge Equal in magnitude to

the negative chare of an electron(same # of protons and electrons)

Determine atoms identity

Neutral Charge

Hold nuclear particles together◦ Proton- Proton force◦ Neutron-Neutron Force◦ Proton-Neutron Force

Nuclear Forces

Counting AtomsCh 3.3

The number of protons of each atom in the element

Z In order on periodic

table

Atomic Number

Atoms of the same element with different number of neutrons(different mass)

Isotopes

Total number of protons and neutrons

Mass Number

Designating IsotopesHyphen Notation Nuclear Symbol

Mass written with a hyphen after the element name

Hydrogen-3◦ 1 Proton◦ 1 Electron◦ 2 Neutrons

Element mass and atomic # written with the elements symbol

Neutrons= Mass-atomic

Practice

Carbon-12 atom◦ Standard to compare

units of atomic mass

Atomic Mass Unit 1amu = 1/12 mass

of Carbon-12

Ex:Oxygen-16◦ Mass 16/12 of

Carbon-12◦ 16 amu

Relative Atomic Masses

Weighted average of atomic masses of naturally occurring isotopes of an element

Calculating AAM

1.Multiply atomic mass of each isotope by relative abundance

2. Add the results

Average Atomic Mass

Relating Mass to Numbers of AtomsMole Avogadro's Number SI unit for amount of

substance

Amount of a substance that contains as many particles as are atoms in 12g of carbon-12

Number of particles in a mole

6.022 x 1023

Relating Mass to Numbers of AtomsMolar Mass Gram/Mole Conversion Mass of 1mole of a

pure substance g/mol

Practice

Practice

Avogadro's Number can be used to find◦ The number of atoms in an element◦ The amount of an element in moles

Conversions with Avogadro's Number

Practice

Practice