Learning Target• Analyze and explain Rutherford’s Gold Foil

Experiment.

Comparison of Atomic Models

Dalton’s Model

Thomson’s Model Rutherford’s Model

J.J. Thomson (IN 1896)A= CathodeB= Anode C= electrical sourceD= Positively charged plateE= negatively charged plate

• http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#

Robert Millikan - 1909

• He measured the charge of an electron.• Using this he gave a negative charge to oil

droplets and was able to measure how different charged plates changed the droplets rate of fall.

• This also allowed him to measure the mass from the charge to mass ratio.

http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#

New Zealand Scientist Ernest Rutherford(1871-1937)

Had performed experiments to find that atoms were made of positively charged particles moving around a very tiny positively charged nucleus.

Rutherford’s Gold Foil experiment

He did an famous experiment whereby he shot a stream of alpha particles at a thin piece of gold (Au) foil expecting most of the particles to be deflected-instead most of them passed directly through the foil and onto the photographic film

Rutherford experiment animation

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

Rutherford’s Atomic Structure Model

+ =positively charged particles- = electrons

• YOU WILL NEED:

–NOTEBOOK

–PERIODIC TABLE

• Protons (positive) are bigger than electrons. The part of an atom that gives an element its identity.

• Neutrons (neutral) are slightly bigger in mass than a proton.

• Electrons (negative) charge, have a mass of close to zero-negligible

Atomic Mass Units (amu): roughly equal to the mass of a proton or neutron.**the mass of an atom is measured in amu’s

1 amu = 1.66x10-24g

Particle Location Charge(C) Mass (g) Mass (amu)

Proton Inside nucleus

1.602 x 10-19 1.673x10-24 1.0073=1

Neutron Inside nucleus

0 1.675x10-24 1.0087=1

Electron Outside nucleus

-1.602 x 10-14 7.109x10-28 0.0006=0

• Every element has a unique atomic number which is the number of protons in the atom.

• Elements atomic number is just above the chemical symbol on periodic table.

• Atoms are electrically neutral-means number of protons always equal number of electrons.

Electron Number

• An Element’s atomic number also indicates number of electron in its atoms.

Ions

•Ions are atoms that have lost or gained one or more electrons giving them a positive or negative charge!

For example: Na (Sodium), has originally 11 electrons but when an electron is lost it becomes a positive ion. Na+

If an ion loses an electron it has a positive charge.

If an ion gains an electron it has a negative charge.

A neutral magnesium atom (atomic number=12) has 12 protons/electrons. If it loses 2 electrons it becomes an ion with a charge of 2+.

Number of protons 12Number of electrons - 10 Charge of Ion 2+

19. Cu²+

20. As3-

29

33

Ion Protons Electrons

27

36

Isotopes• Isotopes are atoms that have the same

number of protons but different numbers of neutrons

• Most elements in the first two rows of the periodic table have at least 2 isotopes with one being more common than the other

• In nature, elements are almost always found as a mixture of isotopes

Differences between isotopes?

• Isotopes react in the same way as others of the same element

Atomic massAtomic Number/number of protons

Atomic mass: weighted average of the masses of the existing isotopes of an element.

• What was Dalton’s 2nd Postulate?

• Was it correct?

Hmmm

• The most common isotope of hydrogen has no neutrons at all

• There's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

Isotopes of Hydrogen

• To identify an isotope more specifically, chemists add a number after the elements name.

ex. Carbon-11 Carbon-12 Carbon-14

• This number is called the isotope’s mass number and is the sum of the isotope’s number of protons and neutrons.

• What is the atomic mass on your Periodic Table?• Which of the 3 isotopes of Carbon is the most

abundant?

Complete Chemical Symbols

14156

Mass number

Atomic number

ChargeBa2+

Number of protons = Atomic #Number of neutrons = Mass # - Atomic #Charge = Atomic # – Number of electrons

Complete the Table

Chemical Symbol

No. of Protons

No. of Electrons

No. of Neutrons

Atom or Ion?

38Sr2+

46 45 50

14 29 Atom

90

WARM UP

• What is the atomic mass unit of a proton? Neutron? Electron?

• What is the atomic mass of an element represent?

Complete the Table

Chemical Symbol

No. of Protons

No. of Electrons

No. of Neutrons

Atom or Ion?

38Sr2+

46 45 50

14 29 Atom

90