Unit 2: Atomic Concepts and Periodic Table (Level 1)



Chemistry 112A

Mrs. Ozment, Mr. Harvey & Mrs. McCall

UNIT 4:

Atomic Concepts Structure

Student Study Guide

Name:

UNIT 4: Atomic Structure

Unit 4 Study Guide: Atomic Concepts & Periodic Table

Vocabulary:

atom

nucleus

subatomic particle(s)

▪ Proton

▪ Electron

▪ Neutron

gold foil experiment

electron energy levels

atomic number

atomic mass

atomic mass unit (amu)

ion

isotope

elements

chemical property

chemical change

What you need to know and be able to do within Unit 4 is listed at the top of each topic page

**TOPIC 1**

Development of the Atomic Model

You Should Know/Understand OR Be Able To Do:

1. Define an atom as the smallest piece of matter retaining elemental properties.

2. Summarize Dalton’s Atomic Theory and relate this theory to models of atoms and compounds learned in Unit 1.

3. Describe the atomic theories of Thomson, Rutherford, and Bohr and relate experimental evidence to the model of the atom.

4. Discuss the structure of an atom including location of the protons, electrons, and neutrons in relation to the nucleus

NOTES:

Atom: smallest particle of an element that retains its properties.

Atoms are so small we have special microscopes to see them.

These pictures of groups of carbon atoms were taken with a TEM (Tunneling Electron Microscope) and an AFM (Atomic Force Microscope).

Notice the scale bar (small black line in lower right of picture). That line represents 2 nm (that’s 2 nanometers.)

If one nanometer equals 1x10-9 meters…

Then 62,500,000 of these pictures would fit in one meter!

That’s REALLY small!!

The Atom – Background & History

A summary of the models of the Atomic Jig-Saw Activity we did in class…

1. The Ancient Greeks Propose a Good Idea - Democritus:

a. He was a Greek smart guy (a philosopher, a thinker) who suggested an indivisible form of matter.

b. He did no “science.” Testing of a good idea did not occur.

ATOMIC MODEL SKETCH:

2. Rediscovering a Good Idea: Dalton and Atoms (1766-1844):

a. He proposed that all elements are composed of a “smallest particle” that could not be further subdivided.

b. He suggested that all atoms of the same element are identical.

c. He noted that atoms of different elements can combine with each other in simple, whole number ratios to form compounds. (Some simple compounds were known about by the early 1800’s. Among the first was ammonia – NH3)

d. Recall particle diagrams:

Chemical reactions (aka “chemical changes”) occur when atoms/molecules are:

1.) separated: **Note that the atoms themselves

remain unchanged!**

2.) joined:

3.) rearranged:

ATOMIC MODEL SKETCH: (Think of a BILLIARD BALL!)

3. Discovery of Subatomic Particles…Dalton’s Undoing…

a. Starting in the late 1800’s, particles smaller than atoms were being detected in experiments.

b. Eventually, this collection of particles was referred to as “sub-atomic” (smaller than atomic) particles.

c. These particles are called electrons, protons and neutrons today.

Discovering Electrons:

Thomson (1897): Experimented with Cathode Ray Tubes (CRTs)

[pic]

A CRT is similar to your TV. It has an anode (A Negative electrODE) and a cathode (A positive electrode). These are enclosed in an evacuated (air removed) glass container and when a charge is applied, the electrons flow from anode to cathode through the open space of the glass container.

Thomson observed these particles and determined that the particles:

• Move at a very high speed (about 10% the speed of light)

• Have a negative charge

• Have a mass of about 1/2000 of a hydrogen atom (hydrogen is the smallest atom)

• Were the same regardless of which gas was used in the container or the metal used as the electrode

The “plum pudding model” attempted to explain atomic structure once the electron (e- or e) had been discovered. An atom, according to this model, was a cluster of small positive and negative charges.

ATOMIC MODEL SKETCH: (Think of a CHOCOLATE CHIP MUFFIN!)

Discovering Protons – The Nucleus:

Rutherford (1911): Performed the Gold Foil Experiment

[pic]

View the online simulations of Rutherford’s Gold Foil Experiment & make observations:

1.

2.

a. Observation #1 –

Conclusion #1 –

**He called this the nucleus.

b. Observation #2 –

Conclusion #2 –

Real-life relation of “mostly empty space”:

If the nucleus is a marble/pea at midfield, the closest electron is at the goal post!

What Rutherford expected to see,

based on Thompson’s chocolate

chip muffin model (

What Rutherford really saw.

Why did some alpha particles

bounce back? How did this change

the model of the atom? (

ATOMIC MODEL SKETCH: (Think of a PEACH!)

Discovering Neutrons:

Chadwick (1932):

a. Subatomic particle with no charge. (Hard to find without a charge!)

b. The nucleus is now considered to be composed of protons and neutrons.

c. This realization led to the “nuclear age” in the 1940s.

4. Bohr (Planetary) Model:

a. Rutherford proposed atoms had a positively charged nucleus, with negatively charged electrons orbiting around it. The only problem: He could not explain why the electrons would not just spiral into the nucleus (since opposite charges attract).

[pic]

b. Bohr used data from atomic spectra to propose a soluton to the flaw in Rutherford’s model

c.Electrons must exist in fixed, stable orbits (or energy levels), which are at a specific distance from the nucleus.

ATOMIC MODEL SKETCH: (Think of an ONION!)

5. Modern Model: (Think of a FAN!)

a. aka - Quantum Mechanical Model, Wave Model, Wave Mechanical Model, Cloud Model, Electron Cloud Model

b. There is a probability for finding the electron in regions of space chemists today call “orbitals.”

Assignment #1 -Discoveries

1. What discoveries concerning the Modern Atomic Theory are each of the following scientists credited with?

a. Ernest Rutherford –

b. John Dalton –

c. J.J. Thomson –

d. Neils Bohr –

2. Draw each atomic model and identify which scientist is associated with it:

|“Nuclear” |“Planetary” |“Billiard Ball” |“Plum Pudding” |

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

|Name of Scientist |Name of Scientist |Name of Scientist |Name of Scientist |

| | | | |

Topic 1: Teachers Sign-Off: ___________________

**TOPIC 2**

Subatomic Particles & Symbols

You Should Know/Understand OR Be Able To Do:

1. Discuss the structure of an atom including location of the protons, electrons, and neutrons in relation to the nucleus.

2. Describe the three basic subatomic particles (protons, electrons, and neutrons) in terms of relative masses and electrical charges.

3. Use atomic number and mass number of an element to find the number of protons, electrons, and neutrons in a particular atom.

Subatomic Particles & Their Properties

| | | |Relative Electrical |Approximate Relative |Actual Mass |

|Particle |Symbol |Location |Charge |Mass |(g) |

| | | | |(amu) | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

• What does the unit “amu” mean?

• Atoms are electrically . This means that the number of

must equal the number of .

• What are “atomic numbers”?

• What are “mass numbers”?

Time for the Reference Tables….open up to the Periodic Table!

Examples of Writing Element Symbols (Notation):

Assignment #2: Atomic Number & Mass Number Worksheet

Complete the following chart and answer the questions below.

|Element |Atomic |Number of |Number of |Number of Electrons |Mass Number |

|Name |Number |Protons |Neutrons | | |

|carbon | | | | |12 |

| |8 | |8 | | |

|hydrogen | | | | |1 |

| | |6 | | |14 |

|hydrogen | | |2 | | |

|nitrogen | | | | |14 |

| | | |1 | |2 |

| |92 | |146 | | |

|cesium | | |82 | | |

| |11 | |12 | | |

| | |47 | | |108 |

|tungsten | | |110 | | |

| | | |45 | |80 |

| | |24 | | |52 |

|Silver | | | | |107 |

| |76 | |114 | | |

1. How are the atomic number and the number of protons related to each other?

2. How do the number of protons, number of neutrons, and the mass number relate to each other?

3. What is the one thing that determines the identity of an atom (that is, whether it is an oxygen atom or a carbon atom, etc.)?

Topic 2: Teachers Sign-Off: ___________________

**TOPIC 3**

Subatomic Particles & Isotopes

You Should Know/Understand OR Be Able To Do:

1. Use atomic number and mass number of an element to find the number of protons, electrons, and neutrons in a particular atom.

2. State how isotopes of an atom differ.

3. Interpret and write isotopic notation.

NOTES:

There are two different naturally occurring types of chlorine atoms, represented by Cl-35 and Cl-37.

➢ What is the difference between these two?!

Isotopes =

“Iso-” is a prefix that means…

So… What are three things that are the same between atoms that are isotopes?

What are two things that are different?

Remember:

1. The number of protons defines the element.

2. The number of neutrons determines which isotope of a given element you have.

ISOTOPES AND ATOMIC MASS

1. Atomic Mass: We need to differentiate between atomic mass and mass (number) of an atom!

Atomic Mass - Mass Number -

2. Look at a Periodic Table....Atomic mass is given to a number of decimal places.

This is because, in most cases, there are a number of naturally occurring isotopes.

For example:

A natural sample of C (atomic mass = 12.011 amu) is a mixture of C-12 (98.89%) and

C-14 (1.11%).

A natural sample of N (atomic mass = 14.007) is a mixture of N-14 (99.63%) and

N-15 (0.37%).

Consider the following periodic table information for carbon:

[Notice on this symbol that the location of the atomic mass and the atomic number seem to be reversed from how it shown on the Periodic Table in our reference tables. Be OK with that… the atomic mass is always the number that is bigger in value, regardless of whether it is above or below the symbol. European and Canadian charts show it this way.]

Carbon's atomic number is 6, has an average atomic mass of 12.011 amu, and carbon's most common isotope has a mass number of 12 amu. Therefore, the most common type of carbon atom has 6 protons, 6 neutrons and 6 electrons. Another naturally-occurring isotope of carbon is C-14, but it is rare in comparison to the amount of C-12 in nature.

|Isotope |Atomic Number |Number of Protons |Number of Neutrons |Number of Electrons |Mass Number (amu) |

| | | | | | |

|[pic] | | | | | |

| | | | | | |

| |8 | |10 | |16 |

| | | | | | |

|[pic] | | | | | |

| | | | | | |

| |17 |20 |18 | | |

4. Fill in the following table:

|Particle |Charge |Mass |Location |

| | | | |

|neutron | | | |

| | | | |

| |+1 |1 | |

| | | | |

|electron | | | |

5. Describe Rutherford’s experiment and his conclusions.

6. How many significant figures in the following numbers:

a. 2.080 b. 0.009 c. 1.009 d. 1800.

7. What is the correct answer (CORRECT NUMBER of SIG FIGS AND UNITS)?

a. The volume of a box which is 1.2 meters long, 0.23 meters wide and 10.6 meters high

b. The density of a piece of metal that weighs 3.456 grams and whose volume is 1.23 ml.

c. The area of a rectangle which is 0.0230 meters long and 1.0230 meters wide

8. Convert the following

a. 2.49 Liters to ______________mL

b. 18.6 mL to ____________Liters

c. 16 cm to ____________meters

9. Calculate the following:

a. Silver has 2 isotopes: Ag-107 has a mass of 106.905 amu and an abundance of 52.00% and Ag-109 has a mass of 108.905 amu and an abundance of 48.00%. What is the atomic mass of silver?

b. Gallium, which has an atomic mass of 69.723 amu, has 2 naturally occurring isotopes, Ga-69 and Ga-71. Which isotope occurs in greater abundance? Explain.

**REMEMBER TO MAKE SURE YOU KNOW/UNDERSTAND

OR ARE ABLE TO DO EACH OF THE OBJECTIVES GIVEN

AT THE TOP OF EACH TOPIC PAGE!**

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Essential Questions for the Unit:

• How has the view of the atom evolved over time?

• What are the parts of an atom, where are they located, and how are the parts held together?

• What are isotopes?

• What is the atomic number for an element?

• What is an ion?

• How is an amu calculated?

• What are electron energy levels and how are they used in chemistry?

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