Chemistry Midterm Short Answers

How was Dalton able to formulate the first atomic theory without performing any experiments himself? What are the four postulates of his atomic theory?

1. All matter is made up of tiny particles called atoms. 2. Atoms of a given element are identical and different from other element's atoms 3. Two or more elements atoms make up compounds. Compounds are always made up of the same types of atoms and same number of atoms. 4. During chemical reactions atoms are never created or destroyed. They are not changed into different types of atoms by chemical reactions. He was able to go straight from hypothesis to theory without experimentation using the previous work of Lavoisier (conservation of matter) and Proust (definite proportions).

You are given two measurements, 2.03 and 203600. How many significant figures are there in each measurement? What can you tell me about the accuracy of each measuring device? Why would the first device be preferred to the second?

2.03 has three significant figures while 203600. has six significant figures. The measuring device for 203600. had more marks and allowed the measurer to get a more accurate measure. The first device may be preferred, if precision and accuracy did not matter as much. It is less accurate to the second. Or if the measurement only required 2 decimal places, the first might be used.

What is a natural law and how does it differ from a theory? Give an example of a Natural Law.

A theory is made after an Observation, Hypothesis, and Experiment; it answers both how and why something occurs. A Natural Law can only answer the how part, we know how this happens, but not why. An example of a Natural Law is gravity. We know how gravity works but do not know why we have gravity.

What is Absolute Zero? What does this point represent? Why are scientists interested in studying the atom's behavior near this theoretical point? Give an example from the video of this behavior.

Absolute zero is the temperature in which motion and heat cease. To find absolute zero, Lord Kelvin removed all pressure thus removing all heat. It can only be reached in theory. It is the lowest temperature possible. Absolute zero occurs at 0 K or -273.15 C or -460 F. Scientists are interested in studying the atom at absolute zero because at absolute zero all particle motion ceases and weird occurrences happen like tights are stretchier, razors are sharper, and golf balls go farther.

What is accuracy and how does it differ from precision? Why is a good measurement considered both accurate and precise?

Accuracy is how close a measurement is to the actual value while precision is how close the measurements are to each other. A good measurement should be close to the actual value, and all measurements should be close to each other.

What is an "equivalency fraction"? How is it created and used? If a cow costs the same amount as 9 goats and a goat costs the same as 72 chickens, what equivalency fractions would you use to see how many chickens you could acquire by selling one cow?

An equivalency fraction is a ration. It is created from equalities and it is used to convert one unit of measurement to another. 1 cow = 9 goats 1 goat = 72 chickens 1 cow = 1 goat 1 cow = 648 chickens 1 cow or 648 chickens 9 goats 72 chickens 648 chickens 1 cow

What is an "exact number"? How does it differ from a measured number? Give an example of an exact number.

An exact number is not measured, and is definitely accurate. An exact number is a counting number, an example is a dozen. A measurement is not exact and cannot be infinitely correct.

Give the complete electron configurations of the following elements: Br and Pb

Br: 1s22s22p63s23p64s23d104p5 Pb:1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2

What is the Celsius scale? What is it based upon? Name one advantage that this scale has over the Fahrenheit scale.

Celsius is widely used in scientific fields. It is based upon 100 degrees C as the boiling point and zero degrees C as melting point. It has advantages over Fahrenheit because it is used by the scientific community, so there is less confusion between switching units. 1C=1K, this is also helpful in science, and is not true on the Fahrenheit scale.

Who proposed the first atomic theory? When did he propose this theory? Why was it so easily dismissed?

Democritus first proposed that there must be a smallest piece of matter in about 400 B.C. Atom comes from atomos (Greek for indivisible). Aristotle said he was wrong and that if there was a smallest piece of matter why didn't we fall apart like sandcastles. And that life was hyle (continuous). He said you could keep cutting smaller as long as you had a sharper knife.

Of the 20 essential elements in the human body, approximately how many elements are essential for the life functions associated with the human body? What is the difference between macro and micro minerals in the human body? What micromineral that is in our body surprised you? Why?

Elements essential for life are carbon, hydrogen, oxygen, nitrogen (those 4 make up 96%), phosphorus, and sulfur. Macro-minerals (calcium, sodium, phosphorus) are representative elements and are involved in bone and teeth formation and are essential. Less common are the micro-minerals (zinc, iron, arsenic). Arsenic is surprising because it is harmful.

What is the Heisenberg Uncertainty Principle and why did he develop this concept?

Heisenberg proposed that it is impossible to know both an electron's position and momentum simultaneously. Electrons absorb energy so easily the best we can say is where it was. Just in the process of detecting electrons, we can give them enough energy to move up a level. He developed this concept to explain why we cannot know both an electron's position and momentum at the same time and to explain why we cannot know an electron's location.

What is Hund's rule? Give an example of Hund's rule.

Hund's rule states that an equal energy orbital must be singly occupied before it is doubly occupied. An electron will not pair if there is an equal energy orbital available. Ex: ↑↓ ↑↓ ↑↓ 1s^2 2s^2 2p^2 Violation of Hund's Rule

Briefly outline how Lavoisier was able to prove the conservation of matter and ultimately disprove phlogiston.

Lavoisier proposed that the fundamental truth of the same amount of matter exists before and after each experiment.Therefore, the fact that calx was heavier than the metal even though phlogiston had left the metal bothered him. He conducted his experiments in public using a huge burning lens that focused the sun's rays to produce intense heat. He placed the calx of lead mixed with charcoal inside a glass vessel partially filled with water.Phlogiston means that heat, smoke and light are released as fire burns. He found that a portion of air was absorbed into the solid material when burning and that was why the calx was heavier than the metal. He finished the theory of phlogiston.

How did Mendeleev organize his periodic table? What did he get wrong when he organized the elements? Why was his organization of the elements still accepted despite this problem?

Mendeleev organized the periodic table in vertical columns. These groups shared family properties. He place iodine and tellurium wrong but decided it was more important for them to be in their proper groups/columns than in correct atomic mass order. If something did not fit, he left it out and was able to make very accurate predictions on what would fit. Moseley fixed his table and organized it by atomic number.

What interesting thing did Moseley discover with his x-ray experiments? How did this change Mendeleev's arrangement of the elements?

Mendeleev's problem was that a few of the elements on the periodic table needed to have the mass reversed. Moseley redefined the periodic table. He found all the x ray spectrums of the elements and arranged the films with wavelengths on them according to their frequency. The dominant x ray lines rose in frequency step by step like a staircase. And all the elements appeared to be where they should be. Moseley proved that the periodic table is actually arranged by atomic numbers, not atomic mass. Chemical properties of elements are dependent on proton numbers.

What are the properties of metals, nonmetals, and metalloids? Give an example of a metal, a nonmetal, and a metalloid:

Metals: typically shiny, solid at room temperature (except Mercury), ductile, malleable, good conductors of heat and electricity, high melting points. Ag, Au, Cu Non-metals: not especially shiny, low densities and melting points, not very ductile or malleable, bad conductors. H, N, O, C Metalloids: exhibits properties of metals and non-metals, better conductors than non-metals but not as good as metals, semi-conductor (can function as insulator or conductor). Sb, Si, Te In chemical reactions: metals tend to lose electrons and form cations; non-metals tend to gain electrons and form anions; metalloids gain/share ions equally

What does temperature truly measure? How is it different from "heat energy"?

Temperature truly measures the speed of particles and this differs from "heat energy" because "heat energy" is determined by mass and speed of particles.

What is meant by the wave particle duality of nature? When does light behave as a particle, a wave?

The EM Spectra is both a particle and a wave. At our normal perception it is a wave, but at the subatomic level it is a particle due to tiny size of quanta.

Why was the Fahrenheit scale the first temperature scale universally adapted? What is the scale based upon? What is one advantage that this scale has over the Celsius scale?

The Fahrenheit scale was adapted first because Daniel Fahrenheit made the first precise glassware to measure with, making his scale more accurate. The 0F point is the temperature at which water and salt freeze. 32F is where just water freezes. It has less negatives than Celsius. It also has more accuracy because the ticks are closer together.

What is the Pauli Exclusion Principle? Give an example of this principle.

The Pauli Exclusion Principle states that an orbital can hold a maximum of 2 electrons. In an orbital with 2 electrons, the electrons must have opposite spins while all orbitals singly occupied, the electrons would have to spin the same way. Ex: ↑↓ ↑↓ ↑↓ 1s^2 2s^2 2p^2 Violation of Pauli Exclusion Principle

What contains a greater amount of energy, an iceberg or a cup of boiling water? Why?

The iceberg contains a greater amount of energy because even though the cup of water has a greater temperature, the iceberg has much more mass. Heat which is a form of energy is determined by speed of particles, mass, and specific heat, therefore the iceberg has more energy.

Why did the lab table feel colder to your hand than your textbook? What does the term cold truly mean?

The lab table felt colder than the textbook because even though they were both about room temperature, they have different specific heats and the table is a conductor, whereas the book is an insulator. The term cold truly means lack of heat.

Identify each of the underlined phrases in the following account of a laboratory procedure as either a chemical change of a physical change. Explain your answers.

The unknown substance was tested to determine its properties. First a sample was ground up finely (Physical: change in appearance) with a mortar and pestle. Next, the samples were dissolved in water (Physical: mixing into a solution) and other solvents. A Bunsen burner was lighted (Chemical: creates an oxidation reaction) and some of the pure chemical was placed into a test tube and heated gently until it melted (Physical: change of state). Because the heating was too rapid, the test tube cracked (Physical appearance/shape change) and the experiment was repeated. Heating was continued until the substance boiled (Physical: change of state). Some of the fumes of the boiling substance reacted with oxygen in the air (Chemical: substance reacting with a compound to create new substance with different properties) to form a white powder.

Why did Rutherford predict the presence of the neutron? Who eventually found the neutron? How did finding the neutron advance atomic theory? What do they believe is the purpose of the neutron in the nucleus?

With the amount of alpha ray particle deflection in the gold foil experiment that there must be something other than protons within the nucleus. James Chadwick found the neutron, this advanced atomic theory because they were able to split the nucleus (nuclear fission, new elements, nuclear weapons). They thought the neutron's purpose was to stabilize the atom.