• YOU WILL NEED:–CALCULATOR–NOTEBOOK–PERIODIC TABLE

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#

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#

Comparison of Atomic Models

Dalton’s Model

Thomson’s Model Rutherford’s Model

Learning Target

• Know the differences between electrons, protons, and neutrons.

• Determine the number of electrons and protons in a neutral atom and ion.

Atom Comparisons

VS.

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

•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.

•Every element has a unique atomic number which is equal to the number of protons.

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

•The individual atom is electrically neutral-means number of protons always equal number of electrons.

How many protons and electrons in the following atoms:

1. Na

2. Pb

3. Os

Ions

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

If an ion looses an election it has a positive charge.

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

How many protons and electrons does a magnesium atom have?

What will the charge be if it loses 2 electrons?

No. of protons -12 (+)No. of electrons - 10 (-) Charge of Ion 2+

Write it like this:Mg2+

19. Cu²+

20. F-

29

9

Ion Protons Electrons

27

10

Learning Target

• Know how the atomic masses on the periodic table are calculated using the isotopes of the element.

• Know how to determine the number of protons, neutrons and electron in an atom or ion.

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

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

VS.

Isotopes•Isotopes are atoms that have the same

number of protons but different numbers of neutrons

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

Penny Isotopes

Analogy the pennies are different atoms of the element penny (Pe).

Step #1 Mass of pennies

1. Record the total number of pennies in your container.2. Separate your penny atoms into 2 categories:

1. 1982 and earlier2. Later than 1982

3. In 2 data tables (1 for pre-1982 and 1 for post-1982) record

the year and mass of each individual penny.

Some years may be duplicated – record each penny individually.

Step #2 Averages

• Calculate the average mass of the pennies in your sample that are 1982 or earlier. This is isotope #1

• Calculate the average mass of the pennies in your sample that are post-1982. This is isotope #2

Step #3 Percentages

• Calculate the percentage of pennies that are pre1982 pennies in your container.

• Calculate the percentage of pennies that are post 1982 in your container.

**KEEP THESE IN DECIMAL FORM.

(0.47 not 47%)

Step #4 Calculate the Average Atomic Mass

• Use the formula:

Average Atomic Mass = (decimal % of 1st Isotope x Average Mass of 1st Isotope) + (% of 2nd Isotope x Average Mass of 2nd Isotope) *Use decimal form of percentage in calculation. .50 not 50%

Atomic massAtomic Number/number of protons

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

•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.

•Which of the 3 isotopes of Carbon is the most abundant?

Differences between isotopes?

•What are the differences between isotopes of the same element?

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

•Do you think that two different isotopes of the same element react the same way?

• Yes they react the same way.

HOW ARE PENNIES AN ANALOGY FOR ISOTOPES?

• What was Dalton’s 2nd Postulate? (page 92)• Was it correct?

Hmmm

Complete Chemical Symbols

14156

Mass number

Atomic number

Charge

Ba2+

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

• YOU WILL NEED:–CALCULATOR–NOTEBOOK–PERIODIC TABLE–3-3 Apply Worksheet

WARM UP

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

• What is the atomic mass of an element represent?

Practice

• What is the chemical symbol for the ion with 13 protons and 10 electrons?

• What is the chemical symbol for the ion with 7 protons and 10 electrons?

• How many protons and electrons are present in the S2- ion?

• How many protons and electrons in Li+ ion?

•Mass Number – the sum of an isotope’s protons and neutrons.

•To name an isotope using chemical symbols, simply place the atom’s mass number to the upper left of the element symbol.

•For example 37Cl.

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