Vocab
Explain the connection between atoms and elements.
Atoms are the building blocks of matter, and all atoms of the same type make up an element.
What is "A property that can be observed and measured directly without considering atoms or molecules."
Macroscopic Property
These molecules: O₂ and C₂ are also compounds. Explain why this statement is correct or incorrect.
A compound must contain atoms of at least two different elements.
Since O₂ and C₂ contain only one type of element, they are molecules but not compounds.
Calculate the average atomic mass of gold with the 50% being gold-197 and 50% being gold-198
197.5 amu
Chlorine has two naturally occurring isotopes, chlorine-35 and chlorine-37. Chlorine-35 is the most abundant isotope of chlorine.
Justify why this claim is correct using concepts of isotopes and average atomic mass.
Evidence: Chlorine has two naturally occurring isotopes, chlorine-35 and chlorine-37. Its average atomic mass is 35.45 amu, which is closer to 35 than 37.
Reasoning: Because the average atomic mass is weighted toward chlorine-35, it must be more abundant than chlorine-37.
Explain the connection between protons and atomic number.
The atomic number of an element equals the number of protons in its nucleus, which identifies the element.
What is a Weighted average of all naturally occurring isotopes of an element
Average Atomic Mass
Particles in a solid are far apart and move freely.” Explain why this claim is incorrect using particle arrangement and motion.
Incorrect. In solids, particles are tightly packed and vibrate in place. They do not move freely and maintain a definite shape and volume.
Why is the mass (in amu) of a carbon-12 atom reported on the periodic table of elements as 12.011 and not as the whole number 12?
12.011 is a weighted average of all the naturally occuring isotopes of carbon. No one atom is exactly 12 amu.
An atom with 6 protons and mass number 12 and another with 6 protons and mass number 14 are both carbon atoms.
Question: Explain why this claim is correct by justifying the difference in mass numbers using protons, neutrons, and isotopes.
Evidence: Both atoms have 6 protons, which identifies them as carbon. The first atom has 6 neutrons (12 − 6 = 6), and the second has 8 neutrons (14 − 6 = 8).
Reasoning: The difference in mass number is due to the different number of neutrons, making them isotopes of carbon.
Explain the connection between neutrons and isotopes.
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.
What is a "Sum of protons and neutrons in an atom."
“A stretched rubber band has potential energy.” Explain why this is correct.
The rubber band stores elastic potential energy because of its stretched position. It is not moving, so it has no kinetic energy yet. The energy can be released when the rubber band snaps.
Hydrogen is 99% 1H, 0.8% 2H, and 0.2% 3H. Calculate its average atomic mass.
1.01 amu
Atoms (the smallest units of elements) combine to form molecules, and molecules combine to form compounds.
Question: Justify why this claim is correct by explaining the relationships between atoms, molecules, elements, and compounds, using examples.
Evidence: An element is made of only one type of atom. Atoms of elements can bond to form molecules (e.g., H₂, O₂), and molecules of elements can combine to form compounds (e.g., H₂ + O → H₂O).
Reasoning: This shows the hierarchy: atoms → molecules → compounds, and connects the concept of elements to the formation of molecules and compounds.
Explain the connection between kinetic energy and thermal energy.
Thermal energy is the total kinetic energy of all particles in a substance, so the motion of individual particles (kinetic energy) contributes to thermal energy.
What is a "Chart that organizes elements by increasing atomic number and similar chemical properties."
Periodic Table
A hot cup of coffee has thermal energy. Explain why this is correct and why it is considered thermal energy.
The particles in the coffee are moving quickly due to heat. This random motion of particles is thermal energy, a form of kinetic energy at the particle level.
Iodine is 80% 127I, 17% 126I, and 3% 128I. Calculate the average atomic mass of iodine.
126.86 amu
Ice floats on water because it is less dense than liquid water. Explain why ice is less dense than liquid water by discussing how the arrangement of water molecules in solid and liquid states affects density.
Evidence: In ice, water molecules form a crystalline lattice that spaces molecules farther apart than in liquid water.
Reasoning: Because the molecules are more spread out, ice has a lower density than liquid water, allowing it to float.
Explain the connection between energy levels and atomic emission spectra.
Electrons move between energy levels when they absorb or release energy, producing the unique pattern of light called the atomic emission spectrum.
What is a "Unique pattern of light emitted when an element’s electrons drop from higher energy levels to lower ones."
Atomic emission spectra
“A chemical battery has stored chemical energy.” Explain why this is correct and why it is potential energy.
Chemical bonds store chemical potential energy, which can be converted into electrical energy when the battery powers a device. It is not yet using the energy, so it is chemical potential energy.
Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%), and 50Ti (5.3%). What is the average atomic mass of titanium?
47.92 amu
Claim: The atomic weight listed on the periodic table represents the weighted average of all naturally occurring isotopes of an element, while the atomic mass refers to the the mass of a specific isotope.
Question:
"Justify why this claim is correct by explaining the difference between atomic weight and atomic mass, using examples of isotopes.
Evidence: Atomic mass is the sum of protons and neutrons in a single isotope (e.g., carbon-12 has 6 protons + 6 neutrons = 12 amu; carbon-14 has 6 protons + 8 neutrons = 14 amu). Atomic weight is the weighted average of all naturally occurring isotopes (e.g., carbon ≈ 12.01 amu).
Reasoning: Atomic weight accounts for the relative abundance of isotopes, whereas atomic mass is specific to one isotope, showing why the two terms are different.