The mystery gift

Have you ever received a gift in a wrapped box and shaken the box to try to guess what may be inside? How would you feel if you could shake the box and measure the box, but you never got to open the box? What if you had to do your best to determine what was in the box and just appreciate it without unwrapping it?

Now imagine what it might be like if the box were incredibly small and what was inside even smaller. Since an atom is too small to be photographed, this was essentially the task undertaken by scientists of the 1800s and early 1900s who studied the atom.

You may have come across diagrams of an atom that are similar to the following diagram presented. What discoveries were made in previous centuries that allow us today to draw an atom as shown in the following diagram?

Scientists studying the atom sought to determine the structure and behaviour of something too small for them to actually observe. Nobody knew the right answer to their questions, so they could only do their best to figure out what was happening on the atomic scale of matter. The collective achievements that uncovered the structure of the atom remain one of the major accomplishments of all science.

Development of the Atomic model

The smallest unit of matter is the atom, just as the smallest meaningful unit of a sentence is a word. A word is made of letters. What is an atom made of? How is an atom organized internally?

Philosophers and scientists have wondered about this for centuries.

We will examine seven major “pieces of the puzzle”, or things that played a role in the development of the atomic model. You will be placed into groups, selected by your teacher, to conduct research into various scientists that have contributed to the atomic model theory as many of these scientists have made other contributions in other areas of science. Use the “Scientists and the development of the Atomic theory” (Opens in new window) to record your research notes. You will place your responses in the following discussion board.

If instead of sunlight you observe light emitted by a heated sample of a pure element, you will notice a distinctive pattern of lines, as in the following images. You can determine from the images that each spectrum has a different pattern of lines specific to the element in the sample.

Each element has its own distinct spectrum. You can use the distinct pattern of lines to determine which element is present in a sample as long as the sample is a pure element.

For many years prior to Rutherford, scientists knew that each element produced distinctive emission spectra but they were unable to explain this phenomenon. It was eventually explained when Niels Bohr combined his knowledge of physics with Rutherford’s conclusions from the gold foil experiment.

These fireworks are orange because of the sodium that is present in the fireworks when they go off.

When various types of matter are burned at high temperatures, they produce flames of different colours. You can use a qualitative analysis technique called a flame test to help determine the presence of a particular metal in an unknown sample by exposing that sample to high temperatures.

Since different metals produce different colours, you can match the known colour that the metal produces to the colour that the unknown sample produces and determine its identity.

Boiling point: >1,000° C

Melting point: <200° C

Density: <0.61 g/cm³

Boiling point: >800° C

Melting point: <100

Density: <0.100 g/cm³

Boiling point: >700° C

Melting point: <100° C

Density: >0.80 g/cm³

Bohr-Rutherford diagram of Hydrogen. Notice how the number of protons and neutrons are indicated within the nucleus. Also notice how the standard notation of the hydrogen atom is provided on the bottom right corner of the image (you will learn more about this later in the learning activity.)

Bohr-Rutherford diagram of Nitrogen. When placing electrons in the second and third orbit of an atom, the first electron is placed at the top of the orbit, the second at the ‘three o’clock position’, the third at the ‘six o’clock position’, and the fourth at the ‘nine o’clock position’. Subsequent electrons are placed in the same fashion, but as pairs. Notice how the fifth electron in the second orbit of nitrogen has been added as a pair for nitrogen.

Example

Draw Bohr-Rutherford diagrams for Helium (2 protons, 2 neutrons, and 2 electrons).

Draw Bohr-Rutherford diagrams for Oxygen (8 protons, 8 neutrons, and 8 electrons).

Draw Bohr-Rutherford diagrams for Chlorine (17 protons, 17 electrons, and 18 neutrons).

The periodic table of elements

Earlier in this learning activity you were asked to investigate the interactive periodic table provided in this course. Explore the following interactive again and examine the Bohr-Rutherford diagrams for the elements.

A change in the number of neutrons has no effect on the atomic number, but it changes the mass number. This is because the atomic number represents the number of protons that the atoms has.

An element’s average atomic mass is listed on the periodic table. This value represents the average of all the naturally occurring isotopes of an element. The mass number for nitrogen is listed as 14.0067. This means that in an average sample of nitrogen there are 7.0067 neutrons for every 7 protons. The decimal value indicates that a sample of nitrogen is actually made up of some atoms that have more or less than 7 neutrons. The mass number listed on the periodic table is an average of all the different forms of nitrogen. Rounding the average mass number provides the mass number of nitrogen, which is 14. For instance, nitrogen-14 is the most common atom in a sample, but a bit of nitrogen-15 also exists. (Note: In the naming of isotopes, a hyphen precedes the mass number when the isotope name is written.) Since the atomic number never changes for nitrogen, the number of protons remains 7 in all isotopes of nitrogen. Therefore, nitrogen-15 has 8 neutrons, one more than the typical nitrogen atom.

All of this information can easily be denoted using standard atomic notation. You have actually encountered this already. In general terms, the standard atomic notation for an element is as follows:

${}_A^{Z}X$

Where Z is the mass number

A is the atomic number

X is the symbol for the element

The following is an example of the standard atomic notation for a fluorine ion with an extra electron:

${\left[{}_9^{19}F\right]}^{-1}$

Where 19 is the mass number

9 is the atomic number

F is the symbol for the element

The square brackets indicate it is an ion, and the superscript “–1” indicates that one extra electron (a negative charge) is present.

In the Minds On section of this learning activity, you were asked to imagine that you had a box and didn’t know what was inside of it. Now, that you have studied the atom in more detail it is time to consolidate your knowledge.

Using the following interactive PhET simulation, press the blue Game component with the happy face.

Initial basic research

Spend a few minutes researching how fireworks work. You will NOT be submitting this report for feedback. It is for practice only.

Evaluating sources of information

Use the following table to learn about the questions you can ask yourself about websites to help you evaluate the sources of information.

*adapted from Purdue OWL; SPARK at York University

Reflection

Review the learning goals and success criteria for this learning activity. Revisit any areas where you need to strengthen your understand.

Now that you have completed the learning activity, reflect on the following success criteria, and make note of your responses in your notebook.