Starter S-23

What are the 3 parts of an atom?

Atomic Structure

Chapter 4

4.1 Defining the Atom

Chapter 4

4.1 Defining the AtomEarly Model

1. Democritus (460-370 B.C.) – matter consists of tiny indivisible, unchangeable particles

2. first to coin term atom

3. Did not use scientific method

4.1 Defining the AtomDalton’s Atomic Theory

Dalton (1766-1844) – used scientific method to support Democritus’s ideas

Most famous for work with the atom, but also worked with

a.Weather

b.Color blindness

4.1 Defining the AtomPostulates of Dalton’s Atomic Theory

1. Elements are composed of tiny indivisible particles called atoms

2. Atoms of the same element are the same, they are different from atoms of any other element

3. Atoms combine in simple whole number ratios to form compounds

4. Chemical reactions join, separate, or recombine atoms, the atoms never change

4.1 Defining the AtomAtoms are very small

Can only be observed with a scanning tunneling microscope

Size is 1 x 10-10m

Or 0.0000000001 m

4.2 Structure of the Nuclear Atom

Chapter 4

4.2 Structure of the Nuclear Atom

Three kinds of sub atomic particles

Proton, Neutron, Electron

Actually many more

Name ofLepton

SymbolMass(MeV)

Electron e 0.511

Electron Neutrino e ~ 0

Muon 106

Muon Neutrino ~ 0

Tau 1,777

Tau Neutrino ~ 0

4.2 Structure of the Nuclear AtomThree kinds of sub

atomic particlesProton, Neutron,

ElectronActually many moreFermions

LeptonsQuarks

HadronsBaryonsMeson

Bosons

Name ofLepton

SymbolMass(MeV)

Electron e 0.511

Electron Neutrino e ~ 0

Muon 106

Muon Neutrino ~ 0

Tau 1,777

Tau Neutrino ~ 0

4.2 Structure of the Nuclear Atom

Electron

Discovered by JJ Thompson (1897)

Negative charge

Very small mass (we will call it 0)

Discovered using a cathode ray tube

Deflects toward the positive plate, so stream of negative particles

Cathode Ray

Simulation

4.2 Structure of the Nuclear Atom

Robert Millikan – preformed experiments to calculate the amount of negative charge

4.2 Structure of the Nuclear Atom

Proton

Positive Charge

Relative Mass of 1 (1840 x electron)

Found in Nucleus

Discovered in 1886 by Eugen Goldstein

Starter S-24

What did each of these scientists contribute to our understanding of the atom?

A. Democritus

B. JJ Thompson

C. Robert Millikan

D. James Dalton

4.2 Structure of the Nuclear Atom

Neutron

Neutral

Found in nucleus

Relative mass is 1

Discovered in 1932 by James Chadwick

4.2 Structure of the Nuclear Atom

In SummaryParticle Symbol Relative

ChargeRelative Mass

Actual Mass

Electron e- 1- 1/1840 (0)

9.11x10-28

Proton p+ 1+ 1 1.67x10-24

Neutron n0 0 1 1.67x10-24

4.2 Structure of the Nuclear Atom

In SummaryParticle Symbol Relative

ChargeRelative Mass

Actual Mass

Electron e- 1- 1/1840 (0)

9.11x10-28

Proton p+ 1+ 1 1.67x10-24

Neutron n0 0 1 1.67x10-24

4.2 Structure of the Nuclear Atom

The Nucleus

Originally believed that all the particles were spread out evenly

1911 Rutherford’s Gold Foil Experiment proved that matter is mostly empty space with a dense positive nucleus

Gold Foil Experiment

Scattering

4.2 Structure of the Nuclear Atom

The Rutherford Model of the Atom

1. The atom is mostly empty space

2. All the positive charge and most of the mass is concentrated in a small nucleus

3. Protons and neutrons are in the nucleus

Called the Nuclear Atom

Does not explain electrons

4.3 Distinguishing Among Atoms

Chapter 4

4.3 Distinguishing Among Atoms

Protons – determine what element is the atom is

Hydrogen – 1 proton

Still Hydrogen if you add

1 Neutron

2 Neutron

4.3 Distinguishing Among Atoms

However, if we add a proton

The element is now Helium

4.3 Distinguishing Among Atoms

Atomic number – the number of protons in an element

This is called the value of Z

A is the mass number

X is the symbol

Hydrogen would beAZ X

4.3 Distinguishing Among Atoms

Atomic number – the number of protons in an element

This is called the value of Z

A is the mass number

X is the symbol

Hydrogen would be11H

4.3 Distinguishing Among Atoms

Atomic number – the number of protons in an element

This is called the value of Z

A is the mass number

X is the symbol

Helium would be11H

4.3 Distinguishing Among Atoms

Atomic number – the number of protons in an element

This is called the value of Z

A is the mass number

X is the symbol

Helium would be42He

4.3 Distinguishing Among Atoms

In a uncharged (neutral) atom, the number of protons equals the number of electrons

If extra electrons are added

Atom becomes negative42He

4.3 Distinguishing Among Atoms

In a uncharged (neutral) atom, the number of protons equals the number of electrons

If extra electrons are added

Atom becomes negative42He

4.3 Distinguishing Among Atoms

In a uncharged (neutral) atom, the number of protons equals the number of electrons

If extra electrons are added

Atom becomes negative

If electrons are lost

Atom becomes positive

42He

4.3 Distinguishing Among Atoms

In a uncharged (neutral) atom, the number of protons equals the number of electrons

If extra electrons are added

Atom becomes negative

If electrons are lost

Atom becomes positive

42He

Starter S-25

How many protons and electrons are in the following atom?

2178

O

4.3 Distinguishing Among Atoms

Mass Number (A) is the total number of protons and neutrons

So hydrogen with no neutrons

With one neutron

11H21H

4.3 Distinguishing Among Atoms

So the number of neutrons is

Neutrons = A – Z

Isotope – same element, but different numbers of neutrons, and different mass numbers

4.3 Distinguishing Among Atoms

4.3 Distinguishing Among Atoms

There are two isotopes of Carbon.

One has a mass of 12, and the other a mass of 13.

What is the symbol for Carbon-12?

How many neutrons

N = A – Z

N = 12 – 6 = 6126C

4.3 Distinguishing Among Atoms

Atomic Mass

Determined using a mass spectrometer

Masses are given relative to the mass Carbon-12

1 amu (Atomic Mass Unit) = 1/12 the mass of 126C

Mass Spectrometer

4.3 Distinguishing Among Atoms

The atomic mass is a weighted average of the mass of different isotopes

Depends on the mass of the isotopes and how common they are

Carbon-12 mass = 12.000, abundance is 98.89%

Carbon-13 mass = 13.003, abundance is 1.11%

011.12144333.08668.11

1443333.00111.0003.13

8668.119889.0000.12

x

x

4.3 Distinguishing Among Atoms

Your turn

Chlorine-35, mass=34.969, abundcance=75.77%

Chlorine-37, mass=36.966, abundance=24.23%

45.359569.8496.26

9569.82423.0966.36

496.267577.0969.34

x

x

4.3 Distinguishing Among Atoms

The Periodic Table

Arranged by increasing atomic number

Columns by similar chemical properties

Periodic Table

4.3 Distinguishing Among Atoms

Period – horizontal row

Group (family) – vertical row

Periodic – chemical properties repeat