Chapter 4.1Chapter 4.1

Defining the AtomDefining the Atom

DemocritusDemocritus (Greece 460 BCE)(Greece 460 BCE)

Believed that atoms were Believed that atoms were indivisible and indivisible and indestructible.indestructible.

Did not explain chemical Did not explain chemical behavior.behavior.

Did not test his ideas with Did not test his ideas with scientific method.scientific method.

Dalton’s Model (1808)Dalton’s Model (1808)

Each element made of Each element made of small atoms. small atoms.

Imagined atoms as tiny, Imagined atoms as tiny, solid balls.solid balls.Like marbles. Like marbles. Each element was Each element was

different.different.

Dalton’s Atomic TheoryDalton’s Atomic Theory

1.1. All elements are composed of All elements are composed of tiny indivisible particles called tiny indivisible particles called atoms.atoms.

2.2. Atoms of the same element are Atoms of the same element are identical. The atoms of any one identical. The atoms of any one element are different from those element are different from those of any other element.of any other element.

3.3. Atoms of different elements can Atoms of different elements can physically mix together or can physically mix together or can chemically combine in simple whole-chemically combine in simple whole-number ratios to form compounds.number ratios to form compounds.

4.4. Chemical reactions occur when atoms Chemical reactions occur when atoms are separated, joined, or rearranged. are separated, joined, or rearranged. Atoms of one element are never Atoms of one element are never changed into atoms of another changed into atoms of another element as a result of a chemical element as a result of a chemical reaction.reaction.

Chapter 4.2Chapter 4.2

Structure of the Nuclear AtomStructure of the Nuclear Atom

Subatomic ParticlesSubatomic Particles

ElectronsElectronsProtonsProtonsNeutronsNeutrons

Subatomic ParticlesSubatomic Particles

ParticleParticle SymbolSymbol RelativeRelative

ChargeCharge

Relative Relative MassMass

Actual Actual MassMass

ElectronElectron

ProtonProton

NeutronNeutron

ElectronsElectrons

J.J.ThomsonJ.J.ThomsonDiscovered the existence of Discovered the existence of

electrons. (1897)electrons. (1897)Tiny, negatively charged Tiny, negatively charged particles.particles.

ProtonsProtons

Ernest Rutherford (1911)Ernest Rutherford (1911)Discovered the location of protons Discovered the location of protons

in an atom.in an atom.Positively charged particles.Positively charged particles.Identified the nucleus of an atom.Identified the nucleus of an atom.

http://chemmovies.unl.edu/ChemAnime/RUhttp://chemmovies.unl.edu/ChemAnime/RUERFD/RUTHERFD.htmlERFD/RUTHERFD.html

NeutronsNeutrons

James Chadwick (1932)James Chadwick (1932)Discovered the existence of Discovered the existence of

neutrons. neutrons. Neutral particles found in the Neutral particles found in the nucleus of an atom.nucleus of an atom.

Chapter 4.3Chapter 4.3

Distinguishing Among AtomsDistinguishing Among Atoms

Atomic Number:Atomic Number: The number of protons in an atom.The number of protons in an atom.This is what identifies each element on the This is what identifies each element on the

periodic table.periodic table.

Examples:Examples:

CC 2727 BrBr6 Cobalt 35

Mass NumberMass NumberThe total number of protons and The total number of protons and

neutrons in an atom.neutrons in an atom.Mass number = protons + neutronsMass number = protons + neutrons

Atomic Mass/Atomic WeightAtomic Mass/Atomic WeightAverage of all the isotope masses of Average of all the isotope masses of

an element.an element.Found on Periodic TableFound on Periodic Table

Round off to nearest whole Round off to nearest whole number to calculate # of neutronsnumber to calculate # of neutrons

Examples of Mass NumberExamples of Mass Number

C-14C-14 1111BB

Calculating Protons, Electrons and Calculating Protons, Electrons and NeutronsNeutrons

Protons = Atomic NumberProtons = Atomic Number

Electrons = # of Protons (for a neutral atom)Electrons = # of Protons (for a neutral atom)

Neutrons = Mass Number - # of protonsNeutrons = Mass Number - # of protons

Mg-24 Ba-137Mg-24 Ba-137

Shorthand Form:Shorthand Form:

C12

6

Practice…Practice…

Shorthand Shorthand SymbolSymbol

Atomic Atomic NumberNumber ProtonsProtons NeutronsNeutrons ElectronsElectrons Mass Mass

NumberNumber

GeGe 7373

2525 3030

3939 5050

7575 186186

IsotopesIsotopes

Atoms that have the same number of Atoms that have the same number of protons (same element), but a protons (same element), but a different number of neutrons.different number of neutrons.They have gained or lost neutrons.They have gained or lost neutrons.They have different atomic masses.They have different atomic masses.

Ions Ions

An atom or group of atoms that has a An atom or group of atoms that has a positive or negative charge.positive or negative charge.

How do atoms become ions?How do atoms become ions?They gain or lose electronsThey gain or lose electrons

Electrons have negative charges.Electrons have negative charges.Gain electron(s)Gain electron(s)negative ionnegative ionLose electron(s)Lose electron(s)positive ionpositive ion

How do we write the symbol for isotopes How do we write the symbol for isotopes and ions?and ions?

Shorthand Form:Shorthand Form:

How many:How many:Protons:Protons:Neutrons:Neutrons:Electrons:Electrons:

F199-1

Atomic number

Mass number

Charge on ion

10

910