Ch. 3: Atoms

3.1 Foundations

HistoryHistory

DemocritusDemocritus named the most basic named the most basic

particleparticle atomatom- means “indivisible- means “indivisible

AristotleAristotle didn’t believe in atomsdidn’t believe in atoms thought matter was thought matter was

continuouscontinuous

HistoryHistory

by 1700s, all chemists agreed:by 1700s, all chemists agreed: on the existence of atomson the existence of atoms that atoms combined to make that atoms combined to make

compoundscompounds

Still did not agree on whether Still did not agree on whether elements combined in the same ratio elements combined in the same ratio when making a compoundwhen making a compound

Law of Conservation of MassLaw of Conservation of Mass

mass is neither created or destroyed mass is neither created or destroyed during regular chemical or physical during regular chemical or physical changeschanges

Law of Definite ProportionsLaw of Definite Proportions

any amount of a compound contains any amount of a compound contains the same element in the same the same element in the same proportions by mass proportions by mass

No matter where the copper carbonate is used, it still has the same composition

Law of Multiple ProportionsLaw of Multiple Proportions applies when 2 or more elements combine applies when 2 or more elements combine

to make more than one type of compoundto make more than one type of compound the mass ratios of the second element the mass ratios of the second element

simplify to small whole numberssimplify to small whole numbers

Law of Multiple ProportionsLaw of Multiple Proportions

Dalton’s Atomic TheoryDalton’s Atomic Theory

1.1. All mass is made of atomsAll mass is made of atoms

2.2. Atoms of same element have the same Atoms of same element have the same size, mass, and propertiessize, mass, and properties

3.3. Atoms can’t be subdivided, created or Atoms can’t be subdivided, created or destroyeddestroyed

4.4. Atoms of different element combine in Atoms of different element combine in whole number ratios to make compoundswhole number ratios to make compounds

5.5. In chemical reactions, atoms are In chemical reactions, atoms are combined, separated, and rearranged.combined, separated, and rearranged.

Modern Atomic TheoryModern Atomic Theory

Some parts of Dalton’s theory were wrong:Some parts of Dalton’s theory were wrong: atoms are divisible into smaller particles atoms are divisible into smaller particles

(subatomic particles)(subatomic particles) atoms of the same element can have different atoms of the same element can have different

masses (isotopes)masses (isotopes) Most important parts of atomic theory:Most important parts of atomic theory:

all matter is made of atomsall matter is made of atoms atoms of different elements have different atoms of different elements have different

propertiesproperties

Ch. 3: Atoms

3.2 Structure of Atom

Structure of AtomStructure of Atom

Nucleus:Nucleus: contains protons contains protons

and neutronsand neutrons takes up very little takes up very little

spacespace Electron Cloud:Electron Cloud:

contains electronscontains electrons takes up most of takes up most of

spacespace

Subatomic ParticlesSubatomic Particles

includes all particles inside atomincludes all particles inside atom protonproton electronelectron neutronneutron

charge on protons and electrons are charge on protons and electrons are equal but oppositeequal but opposite

to make an atom neutral, need equal to make an atom neutral, need equal numbers of protons and electronsnumbers of protons and electrons

Subatomic ParticlesSubatomic Particles

number of protons identifies the atom as a number of protons identifies the atom as a certain elementcertain element

protons and neutrons are about same sizeprotons and neutrons are about same size electrons are much smaller electrons are much smaller nuclear forcenuclear force- when particles in the - when particles in the

nucleus get very close, they have a strong nucleus get very close, they have a strong attractionattraction proton + protonproton + proton proton + neutronproton + neutron neutron + neutronneutron + neutron

Atomic RadiusAtomic Radius size of atomsize of atom measured from center of nucleus to outside of measured from center of nucleus to outside of

electron cloudelectron cloud expressed in picometers (10expressed in picometers (101212 pm = 1 m) pm = 1 m) usually 40-270 pmusually 40-270 pm

ExampleExample

An atom has a radius of 140 pm. An atom has a radius of 140 pm. How large is that in meters?How large is that in meters?

mpm

mpm 1012

12104.110140

10

1140