Chemistry 1-2: Modeling Atoms

Section 1-2: Modeling Atoms

Multiple Choice

211 lb=? kg
1kg =2.2 lb

• 95794.0
• 95.90
• 9.59x10^-11
• .9590

Multiple Select

Which items below represent an element and NOT a molecule? (Select all that apply)

• F

• O₃

• Ca

• NH₃

• CO₂

Multiple Choice

Which of the following best describes matter?

• Anything that has volume.

• Anything that has definite weight.

• Anything that can be turned into liquid.

• Anything that has mass and occupies a space.

Multiple Choice

What is the most important law in chemistry?

• The law of conservation of mass

• the law of reactions

• the electron cloud law

• the periodic law

Multiple Choice

Which scientist developed the Modern atomic theory?

• JJ Thomson
• Ernest Rutherford
• John Dalton
• Democritus

• Aristotle

Lesson Objectives

• Review the Parts of the atom

• Calculate the atomic mass of an atom

• Define an Isotope

• Describe the difference between an atom and its isotope

Subatomic Particles

• Atoms are made up of smaller particles called subatomic Particles

  • Protons

  • Electrons

  • Neutrons

Electrons

• Have a negative charge

• Were the first subatomic particles discovered

  • Found through studies in electricity by J. J. Thomson

    • Created Cathode rays that emit light from the negative end to the positive end

• Electrons have a mass of 9.109 × 10^-31 kg

Protons

• Are Positively Charged

• Not really discovered as much as inferred to exist once electrons were discovered

  • All atoms are neutral, but electrons have a negative charge, so there have to be particles with a positive charge to cancel out the electrons

The Plum Pudding Model

• Thomson knew that electrons and protons existed in atoms, but did not know how.

• Proposed the "Plum Pudding" Model

  • Electrons and Protons just mixed

  • Explained why the atom was neutral, but not why it had mass

Rutherford's Gold Foil Experiment

• Ernest Rutherford

  • A student of Thomson

• 1911- Preformed an experiment where he shot a piece of foil with a laser of negative charges

  • Most passed through the foil, but some bounced back

• Rutherford concluded that the beam was hitting a mass in the center where the protons were

  • Called this mass the nucleus

Visualizing the Atom

• Two parts to the atom

  • Nucleus: The center of the atom, contains most of the mass

    • made up of protons and neutrons

  • Electron Cloud: Surrounds the nucleus

    • holds the electrons orbiting the nucleus​

Multiple Choice

Subatomic particles with a negative charge are called....

• Electrons

• Neutrons

• Protons

• Quarks

• Negatrons

Multiple Choice

What did Thomson discover?

• electron
• proton
• neutron
• electron cloud

Multiple Choice

This is the subatomic particle with a positive charge

• Proton

• Neutron

• Electron

Multiple Choice

Which Scientist discovered the nucleus of the atom?

• JJ Thomson

• Isaac Newton
• Democritus

• Ernest Rutherford

Multiple Choice

This is the subatomic particle with a neutral charge

• Proton

• Neutron

• Electron

Types of Atoms

• The number of protons in an atom are what determines the type of element it is

  • Atomic Number: The number of protons in an atom

    • Example: Hydrogen has 1, Sodium has 11

• All elements have a neutral charge, therefore, they have to have the same number of electrons as protons

  • Hydrogen has 1 proton, so it has 1 electron​

The Periodic Table

• There are currently 118 known elements, all with different atomic numbers arranged on a periodic table

  • The Periodic Table: an arrangement of the elements in which the elements are separated into groups based on sets of repeating properties

    • Elements are listed in order of atomic number

Mass Number

• Most of the mass in an atom comes from protons and neutrons

• The Mass Number: the total number of Protons + the total number of Neutrons

  • Usually, if you know the number of protons, you can use the periodic table to figure out the number of neutrons

  • Mass is measured in atomic mass units (amu)

Multiple Choice

Find the element with the atomic number of 8

• Oxygen

• Sulfur

• Beryllium

• Lithium

Multiple Choice

Find the element with 16 electrons

• Oxygen

• Sulfur

• Beryllium

• Lithium

Multiple Choice

The atomic number tells you how many ________ an element has

• Protons

• Neutrons

Isotopes

• All atoms of an element have the same number of protons, but they can have different numbers of neutrons

• Isotopes: atoms that have the same number of protons but different numbers of neutrons

  • The different number of neutrons means​ they have different masses as well

  • Isotopes are identified by their mass number

    • Example: Hydrogen-3, Carbon-14

Isotopes & Atomic Mass

• It is not easy to compare the mass of single atoms because they are so small

  • It is more useful to compare the masses of atoms using a reference isotope that can be easily measured accurately

    • Carbon-12: The isotope used to compare the relative masses of all atoms

      • has a mass of 12 atomic mass units amu​

Reading and Writing Isotopes

• There are two ways to write an isotope

  • Using the Elemental symbols

    • On the left side of the chemical symbol: Put the mass on top, the atomic number on the bottom

  • Using the element name

    • Hyphenated with the mass

      • example: Hydrogen-3

Isotopes-Sample Problem 1

• How many protons, electrons, and neutrons are there in an atom of chlorine-37?

  • The atomic number tells us how many protons are in any element, no matter what

  • Step 1: Find the atomic number of Chlorine using the periodic table

Isotopes-Sample Problem 1

• How many protons, electrons, and neutrons are there in an atom of chlorine-37?

  • The atomic number tells us how many protons and electrons are in any element, no matter what

  • Step 1: Find the atomic number of Chlorine using the periodic table

    • Chlorine has a mass of 17

  • Step 2: Determine the mass of Chlorine-37

    • Look at the name

  • Step 3: Use the equation for the mass of an isotope

    • isotope mass= protons + Neutrons

Isotopes-Sample Problem 2

• Calculate the number of protons, electrons, and neutrons in oxygen-17

  • Step 1: Identify how we find the information

Categorize

Options (3)

Protons

Electrons

Neutrons

Organize these options into the right categories

Look at the Atomic Number

Atomic Mass-Atomic numner

Isotopes-Sample Problem 2

• Calculate the number of protons, electrons, and neutrons in oxygen-17

  • Step 1: Identify how we find the information

  • Step 2: Solve for the information we need

    • Protons=Atomic number

    • Electrons=Atomic Number

    • Neutrons=Atomic Mass-Atomic Number

Multiple Choice

What is the Atomic number of Oxygen?

• 16

• 10
• 12
• 8

Multiple Choice

What is the Atomic Mass of Oxygen? (Round to a Whole Number)

• 16

• 10
• 12
• 8

Fill in the Blanks

Fill in the Blanks

Fill in the Blanks

Fill in the Blanks

Isotope Abundance and Atomic Mass

• In nature, most elements occur as a combination of two or more isotopes

  • Each isotope has a natural percent abundance​

• The average atomic mass is the weighted average of the masses of its isotopes

  • a weighted average reflects the relative abundance of each isotope found in nature

• Calculated Atomic Mass: The more common an isotope is, the more important it is in atomic mass calculations

  • Step 1: ​multiply the mass of each isotope by its natural abundance

  • Step 2: add the products of all the weighted isotopes masses

Atomic Mass Estimations Practice Problem 1

• Element X has two naturally occurring isotopes. One isotope has a mass of 10 amu with a relative abundance of 20%. The other isotope hasa mass of 11 amu and relative abundance of 80%. What is the average atomic mass of Element X

  • Step 1: Multiply the masses of each isotope by its relative abundance

    • 10 x 0.20=2​

    • 11 x 0.80= 8.8

  • Step 2: Add the two relative masses together

Atomic Mass Estimations Practice Problem 2

• Consider a hypothetical element, X, that has three isotopes. Calculate the weighted- average atomic mass of the element from the following data:

  • ​Step 1: Multiply each atomic mass by it's abundance

    • 85.32 x 0.10

    • 87.51 x 0.70

    • 88.10 x 0.20

  • Add the sum of the relative masses together

Chem 1 | Unit 1 Lessons 2 & 3

​Isotope	​Abundance	​Atomic Mass
​X-85	​10%	​85.32 amu
​X-87	​70%	​87.51 amu
​X-88	​20%	​88.10 amu

Fill in the Blanks

Open Ended

Explain in your own words how our understanding of atoms has changed over time. Write at Least 3 Sentences