UNIT 1: Atoms, Patterns, and the Periodic Table

Part 1

Chemistry Fall 2015


Unit 1: Atoms, Patterns, and the Periodic Table

KUDos are a way organizing our learning goals. By the end of this unit, you should:

KNOW: Things you need to ‘know’ are facts that you need to memorize and recall. They are like the ingredients in a recipe. You cannot ‘understand’ or ‘do’ without these basics.

Chemistry
Property
Atom
Atomic Number / Proton
Neutron
Electron
Valence Electrons / Isotope
Mass Number
Average Atomic Mass
Atomic Sketch

UNDERSTAND: Things you need to ‘understand’ are big picture generalizations you need to generate. This is like the recipe. It is the big picture/plan. This understanding helps you do the ‘do’.

  1. Matter is classified by its physical and chemical properties.
  2. Evidence gathered over hundreds of years has helped us to produce an ever more accurate model of the atom.
  3. The physical and chemical properties of substances result from the types and arrangement of atoms in the substance.

DO: The things you need to ‘do’ are skills and processes that you need to independently do. These are like the different actions you do to actually make a meal. You will be tracking your progress in the table below and you can check them off when you see you are ready for the quiz.

1)Define vocabulary words in the KNOW section.

2)Provide evidence for the structure of the atom. (protons, electrons, , neutrons, nucleus, mostly empty space)

3)Identify an element and its number of protons, electrons, neutrons, and mass number if you are given its atomic number

4)Create/draw a model of an atom that accurately shows the number & placement of protons, neutrons, and electrons

5)Draw an atomic sketch that represents the correct number of energy levels and number of electrons in each energy level.

CCRS SKILLS

E.24.5 Determine which model(s) is(are) supported or weakened by new information

KNOW: Chemistry, Property

Baggie Lab

An Introduction to Chemistry

PreLab Questions: Answer these question based on your experience. There are no right or wrong answers to these questions.

  1. Based on your experience, what do you think chemistry is?
  2. What do you think chemists do?
  3. What things are important when designing an experiment?

Purpose:To investigate the unique properties of substances when they are alone vs combined with other substances.

Materials:

  • 1 dropper bottle ofBTB (bromthymol blue)
  • 1 beaker of water
  • calcium chloride (CaCl2)
  • baking soda (sodium bicarbonate- NaHCO3)
  • 1-qt Ziploc bag

Procedure Part I

  1. Record observations of each substance before the reactants are mixed.

Initial Observations

Calcium chloride
CaCl2 / Baking soda
NaHCO3 / Water
H20 / Bromthymol Blue Solution (BTB)
  1. Place a 1-quart Ziploc flat on the lab counter
  2. Fill a spoon up to the BLACK line with baking soda and place into a corner of the Ziploc baggie.
  3. Fill a spoon up to the BLUE line with calcium chloride and place into a second corner of the baggie.
  4. Carefully inject 5 drops of bromthymol blue solution into a third corner of the baggie.
  5. Carefully inject ONE pipet-full of water into the fourth corner of the baggie.
  6. Quickly and gently close the baggie, keeping all four items separate.
  7. Pick the baggie up off of the table. Holding the baggie upright, mix all four ingredients and record your observations.
  8. Carefully wash out the baggie and dry the inside of it with a towel.
  9. Repeat the experiment, leaving out 1, and only 1, ingredient each time. Record your observations for each trial in the following table. Place a checkmark in each box if the substance was used, and a ----- if it was not used.

Data and Observations:

Part I Trials / CaCl2 Baking soda Water BTB / Observations
1 / / / /
2 / / / /
3
4
5
  1. For the Part II trials, leave out 2 ingredients for each trial.

Part II Trials / CaCl2 Baking soda Water BTB / Observations
1 / / / /
2
3
4

Questions:

  1. Based on your observations, Can you tell
  2. Which ingredient is responsible for the rise in temperature? Explain.
  1. Which ingredient is responsible for the drop in temperature? Explain.
  1. Which ingredient is responsible for the color changes? Explain.
  1. Which ingredients are required to produce all the changes in Experiment #1?

Class definition of chemistry:

Class definition of property:

KNOW: Atom, Property

UNDERSTAND: The physical and chemical properties of substances result from the types and arrangement of atoms in the substance.

Why do we care about atoms?

We have seen that different substances have different properties, or characteristics. But why? We are going to make the connection between the properties we can see with our own eyes, and the scale of atoms. An atom is the smallest unit of an element that maintains the chemical properties of that element. In other words, it’s the smallest possible piece of an element, and cannot be broken down. Sometimes people use the term “nanoscale” to describe the atomic level, since atoms are generally only a nanometer in length. That’s one billionth of a meter, so pretty tiny! But can such tiny particles really make a difference?

We are going to use everyday objects to stand for atoms and the different ways they can be arranged.

  1. Place two cups upside down, about 1 inch apart.
  2. Peel off 2 Post-it notes and stack them as a flat bridge between the cups.
  3. Place pennies one at a time on the middle of your Post-it note bridge. When the structure falls, count how many pennies you used.
  4. Roll up 2 Post-it notes. Use a pen or pencil to help roll the tubes, and use the sticky ends to seal the tubes closed.
  5. Place the tubes across the gap between the cups.
  6. Place pennies one at a time over your bridge. Like you did before, count how many pennies the bridge could hold.

Which bridge was stronger? Why do you think this is?

Imagine that your Post-it notes are made of millions of tiny carbon atoms (which, they sort of are, since paper is largely made of carbon). The Post-its left as sheets are more like graphite, which is what we call pencil “lead.” In graphite, carbon atoms are arranged in hexagons that join together in sheets, like in the picture on the left below:

Because graphite is arranged in sheets, it’s easy for those sheets to slide past each other, and graphite is kind of brittle. On the other hand, carbon can also be arranged in rolls of those hexagons, just like how you rolled up the Post-it. As you saw, this structure is much stronger. We call carbon in this form carbon nanotubes, or CNT. It’s what makes really tough hockey sticks.

As you can see, it’s not only the type of atoms you have, but also how they are arranged at that tiny nanoscale that affects properties like strength. We choose different materials for different purposes based on their properties.

So let’s back up and find out…what IS an atom in the first place? In the drawings above, small dots are used as a symbol for atoms, but what do they really look like?

READING: Main Ideas of Five Models of the Atom

We are going to be learning about how models of the atom have changed through time, and practice a CCRS skill. But before we do that, let’s get familiar with main ideas of the models we will be working with.

Use your Five Models of the Atom handout to complete the table below. The first row is completed for you as an example.

Model / Main Idea (MI.24.1) / Supporting Details (SD.20.1)
Solid sphere / The atom is a solid sphere. / Atoms cannot be broken into smaller pieces.
Plum pudding
Nuclear
Proton
Solar System

GOAL: E.24.5 Determine which model(s) is(are) supported or weakened by new information

GOAL 2: Provide evidence for the structure of the atom. (protons, electrons, neutrons, nucleus, mostly empty space)

Models of the Atom: How do we know what an atom looks like?

Use model descriptions on from your Models handout as we go along.

Background:

In 1803, John Dalton proposed that atoms were simply solid spheres. In the decades that followed, chemists collected a lot of evidence suggesting that there was more to the atom. We will look at the five models of the atom, read their descriptions, and watch short videos about how the pieces of evidence were collected. Then we will use the evidence to evaluate the models. It’s important to remember that scientists are still adding to our knowledge of what an atom looks like, so the model can still change!

EVIDENCE 1: It is possible to remove a negatively charged particle from an atom using electrical forces. (Thomson, 1897)

1. Does the evidence better support the solid sphere model or the plum pudding model?

Let’s break it down:

  1. Main characteristics of the solid sphere model (E.20.2):
  1. Main characteristics of the plum pudding model (E.20.2):
  1. Main idea of evidence 1 is that atoms must contain ______.
  1. Which model best matches evidence 1, based on your answer above? Explain.

EVIDENCE 2: If a tiny particle is shot into the middle of an atom, it hits something dense in the center and bounces back in the direction from which it came. If a tiny particle is shot into the edges of the atom, it goes through. Most tiny particles shot at an atom will go through. (Rutherford, 1911)

2. Does the evidence better support the nuclear model or the plum pudding model?

a. Main characteristics of the nuclear model (E.20.2):

b. Main characteristics of the plum pudding model (E.20.2):

c. Main ideas of evidence 2 are that the atom’s parts are most concentrated in its (center, edges) and that the edges of the atom must contain mostly (particles, empty space).

d. Based on your answers above, which model is best supported by evidence 2? Explain.

3. EVIDENCE 3: Some electrons are easier to remove from an atom than others, suggesting that some electrons are farther from the center of an atom than others. (Bohr, 1913)

This time, let’s identify whether evidence 3 supports or weakens each model:

  1. Solid sphere model (supported/weakened). Explain your choice:

Example: Evidence 3 shows that there are smaller particles within the atom, but the solid sphere model has no particles.

  1. Plum pudding model (supported/weakened). Explain your choice:
  1. Nuclear model (supported/weakened). Explain your choice:
  1. Proton model (supported/weakened). Explain your choice:
  1. Solar system model (supported/weakened). Explain your choice:

EVIDENCE 4. In 1932, British physicist James Chadwick discovered that the nucleus was made up of uncharged, or neutral, particles called neutrons, in addition to the protons discovered by Rutherford. He also knew about Bohr’s experiments with removing electrons from atoms.

Which model(s) is(are) supported or weakened by evidence 4?

  1. Plum pudding model (supported/weakened). Explain your choice:
  1. Proton model (supported/weakened). Explain your choice:
  1. Solar system model (supported/weakened). Explain your choice:
  1. Which model is the closest match with evidence 4? Why?
  1. How could you revise the model so that it incorporates evidence 4? Draw a picture of an atom based on your model, and give it a name.

Goal 2: Provide evidence for the structure of the atom. (nucleus, protons, electrons, neutrons, mostly empty space)

Fill in the table to describe the pieces of evidence which support the existence of each part of the atom.

Part of Atom / Pieces of Evidence that support it / Is it located in the nucleus or outside the nucleus? / What is its charge? (positive, negative, neutral)
Nucleus
Electron
Proton
Neutron
Mostly empty space

Use the space below to draw important parts of the experiments that gave us the evidence.

Draw Rutherford’s gold foil experiment:

Draw Thomson’s cathode ray experiment:

How do we know the nucleus is made of both protons and neutrons?

Practice: Evidence for the Structure of the Atom

GOAL 2: Provide evidence for the structure of the atom. (protons, electrons, neutrons, nucleus, mostly empty space)

  1. Rutherford’s gold foil experiment
  2. Explain the experiment in words
  1. List the conclusions of the Rutherford experiment
  1. Cathode Ray experiment
  2. Explain the experiment in words
  1. List the conclusions of the cathode ray experiment

  1. Rutherford’s gold foil experiment provided
evidence that the atom consisted of a
  1. A small, positive nucleus
  2. Mostly empty space
  3. Electrons moved freely
  4. A and B
  5. A, B, and C
/
  1. The cathode ray experiment provided evidence that the atom consisted of :
  2. A small, positive nucleus
  3. Neutrons that were neutral
  4. Electrons that were negative
  5. Protons that were positive
  6. All of the above

  1. The conclusion that there was a positive nucleus from Rutherford’s experiment was because:
  2. The alpha particles were positive and repelled the nucleus.
  3. The alpha particles were negative and were attracted to the nucleus.
  4. The alpha particles were positive and were attracted to the nucleus.
  5. The alpha particles were neutral so they didn’t have an effect on the nucleus.
/
  1. Neutrons were discovered based on an experiment with alpha particles, too. Neutrons are needed to make the nucleus stable because:
  2. The negative protons would be attracted to each other.
  3. The positive protons would repel each other.
  4. The positive protons would be attracted to each other.

GOAL: E.24.5 Determine which model(s) is(are) supported by new information

Directions: As you read the passage, summarize the supporting details of each model in the margin so it will be easy for you to find the information you need later. One supporting detail is given for you.

Passage: Explaining the Extinction of the Dinosaurs

Asteroid-Impact (AI) Model

The dinosaurs disappeared at the end of the Mesozoic era, about 65 million years ago. The disappearance took place over a very short period of time and was, according to some scientists, triggered by Earth colliding with a large asteroid.

Today, evidence of this collision can be found in the rock record. Geologists have discovered a thin layer of clay containing a high concentration of the element iridium between 2 particular rock layers. This boundary marks the end of the Mesozoic and the beginning of the Cenozoic era. This iridium-rich layer has been identified at the Mesozoic-Cenozoic boundary at many different locations around the world. Iridium, while rare on Earth, is a common substance in meteorites and asteroids.

The asteroid not only supplied the iridium, but its white-hot rock fragments also started fires that engulfed entire continents. The soot from these fires, combined with asteroid particles that were propelled into the atmosphere, blocked out the Sun’s energy. The lack of sunlight halted photosynthesis and caused a decrease in global temperatures. Much of the plant and animal life, including the dinosaurs, could not adapt to the temperature change and died.

Gradual-Extinction (GE) Model

Some scientists disagree with the asteroid-impact model. They point to evidence that the dinosaurs died out gradually because of a long-term climatic change.

Earth experienced increased volcanic activity 65 million years ago. Not only could Earth’s volcanism have produced the iridium, but more important, volcanoes did produce tremendous amounts of carbon dioxide. The increased levels of carbon dioxide in the atmosphere prevented Earth from radiating excess heat back into space, and thus caused a worldwide warming.

The warming of Earth is what caused the dinosaurs’ disappearance. After examining dinosaur egg fossils, paleontologists discovered that the eggshells became thinner in at least one species. This was thought to be the result of heat adversely affecting the dinosaurs’ metabolism. These thin-shelled eggs, which were easily broken, lowered the survival rate among the offspring and contributed to the eventual extinction of the dinosaurs.

Now choose the best answers to the questions, explaining your choices.

1. Astronomers recently estimated that only 3% of asteroids with orbits that intersect Earth’s have been identified. Which model is supported by this evidence?

A. The asteroid-impact model

B. The gradual extinction model

C. Both models are supported by the new information

D. Neither model is supported by the new information

2. A geologist examines a sedimentary rock layer from the Mesozoic-Cenozoic boundary, finding evidence of great volcanic activity. Which model, if any, would most likely be in agreement with this evidence?

A. The asteroid-impact model

B. The gradual extinction model

C. Both models

D. Neither model

3. Which piece of evidence do BOTH models suggest as a direct cause of the extinction of the dinosaurs?

A. High levels of soot and volcanic ash

B. High concentrations of iridium

C. Global temperature change

D. Increased amounts of carbon dioxide introduced into the atmosphere

4. Some massive object periodically disrupts the solar system, causing comets and asteroids to enter the inner solar system. Which model is weakened by this information?