Anna and Ben are two high school students who are curious about the atom. They decide to do some experiments with different materials and instruments to learn more about this topic.
They start by using a magnifying glass to observe some small objects, such as a grain of salt, a piece of sugar, and a strand of hair. They notice that they can see the shape and texture of each object, but they cannot see the individual atoms that make up the object. They wonder how small atoms are and how many of them are in each object.
They use a calculator to estimate the size and number of atoms in each object. They learn that atoms are very small, about 0.1 nanometers in diameter, and that a nanometer is one billionth of a meter. They also learn that there are about 6.02 x 10^23 atoms in one mole of any substance, and that a mole is a unit of measurement for the amount of substance. They use the molar mass of each substance to calculate how many moles and atoms are in each object. They record their results in a table:
| Object | Mass (g) | Molar mass (g/mol) | Moles | Atoms |
|--------|----------|--------------------|-------|-------|
| Salt | 0.1 | 58.44 | 0.00171 | 1.03 x 10^21 |
| Sugar | 0.1 | 342.3 | 0.000292 | 1.76 x 10^20 |
| Hair | 0.1 | 113.16 | 0.000884 | 5.32 x 10^20 |
They are amazed by the large numbers of atoms in such small objects. They also notice that different substances have different molar masses, which depend on the type and number of atoms in each molecule. They wonder what kinds of atoms are in each substance and how they are arranged.
They use a computer program to visualize the molecular structure of each substance. They learn that salt is made of sodium and chlorine atoms, sugar is made of carbon, hydrogen, and oxygen atoms, and hair is made of nitrogen, carbon, hydrogen, oxygen, and sulfur atoms. They also learn that atoms are bonded together by sharing or transferring electrons, which are negatively charged particles that orbit the nucleus of the atom. They see that the nucleus of the atom contains protons, which are positively charged particles, and neutrons, which are neutral particles. They record the number of protons, neutrons, and electrons in each atom in another table:
| Atom | Protons | Neutrons | Electrons |
|------|---------|----------|-----------|
| Sodium | 11 | 12 | 11 |
| Chlorine | 17 | 18 | 17 |
| Carbon | 6 | 6 | 6 |
| Hydrogen | 1 | 0 | 1 |
| Oxygen | 8 | 8 | 8 |
| Nitrogen | 7 | 7 | 7 |
| Sulfur | 16 | 16 | 16 |
They compare the two tables and realize that the number of protons determines the identity of the atom, and that the number of protons and neutrons determines the mass of the atom. They also realize that the number of electrons determines the charge of the atom, and that atoms are neutral when they have equal numbers of protons and electrons. They learn that the number of protons is called the atomic number, and that the sum of protons and neutrons is called the mass number. They also learn that some atoms can have different numbers of neutrons, which are called isotopes.
Anna and Ben are satisfied with their experiments and feel that they have learned a lot about the atom. They decide to write some questions and answers based on their observations to test their knowledge. Here are some examples:
Q: What are the three main subatomic particles in an atom?
A: Protons, neutrons, and electrons.
Q: What are the charges of each subatomic particle?
A: Protons are positive, neutrons are neutral, and electrons are negative.
Q: What are the units of measurement for the size and number of atoms?
A: Nanometers and moles.
Q: What is the name of the unit that represents 6.02 x 10^23 atoms?
A: Avogadro's number.
Q: What is the name of the formula that relates the mass, molar mass, and number of moles of a substance?
A: Molar mass = mass / moles
Q: What is the name of the formula that relates the number of moles, Avogadro's number, and number of atoms of a substance?
A: Number of atoms = moles x Avogadro's number
Q: What is the name of the center of the atom that contains protons and neutrons?
A: Nucleus.
Q: What is the name of the region around the nucleus that contains electrons?
A: Electron cloud.
Q: What is the name of the number that represents the number of protons in an atom?
A: Atomic number.
Q: What is the name of the number that represents the sum of protons and neutrons in an atom?
A: Mass number.
Q: What is the name of the atoms that have the same number of protons but different numbers of neutrons?
A: Isotopes.