Physics Assignment Answers

Chapters 17 & 18

Ch 17 Review Answers:

  1. There are about 110 different elements known today.
  2. Hydrogen (H) is the element with the lightest atoms. It is also the most plentiful element in the Universe.
  3. Most atoms are much older than the Solar System.
  4. Atoms are "recyclable"! The atoms that make up your body were probably created billions of years ago in a violent stellar explosion - they were not created when you were born. When you die, "your" atoms continue to exist. Therefore, you don't own the atoms that make up your body - you are merely using them for a while.
  6. Atoms are much smaller than the wavelengths of visible light. This means that atoms cannot be seen in visible light.
  7. Dust and pollen particles move with Brownian motion when suspended in water because they are bombarded by the tiny-but-fast-moving water molecules around them.
  8. Images showing individual atoms, such as Figure 17.3, were not produced with a conventional microscope since individual atoms are too small to be seen with visible light. These images are produced by a computer using data from an instrument that uses waves with much smaller wavelength than visible light.
  15. Since protons and neutrons are much more massive than electrons (about 2000 times as massive), the mass of the nucleus and the mass of the entire atom are about the same. In other words, almost all of the mass of the atom is contained in the nucleus.
  16. Even though almost all of the mass of the atom is contained in the nucleus, the size of the nucleus is extremely tiny compared to the size of the atom. In other words, the atom is mostly empty space.
  17. Protons and neutrons are the two kinds of nucleons.
  18. a) An isotope of an element is an atom which contains a non-typical number of neutrons.
  19. The atomic number of an atom equals the number of protons in the atom's nucleus, and also equals the number of electrons in a normal atom.
  20. The mass of the electron is about 1/2000 the mass of a nucleon.
  21. a) An ion is an atom which has different numbers of protons and electrons.
  25. The four common phases of matter are solid, liquid, gas, and plasma.

Chapter 18 Review Answers:

  1. In a crystalline solid, atoms have a regular geometric arrangement. In a non-crystalline solid, they don't.
  2. Regular geometric patterns made by X-rays reflected from the surfaces of crystals are evidence of the geometric arrangement of atoms in a crystal. More recently, instruments such as scanning tunneling electron microscopes have enabled scientists to create images of individual atoms (as in chapter 17), which also presents strong evidence for the arrangement of atoms.
  3. Evidence for large-scale crystal structure in solids includes rock crystals and the etched surfaces of some metals.
  4. When a uniform piece of wood is cut in half, its density stays the same. The cut piece of wood has half the mass (or half the weight), but it also has half the volume. Density = mass (or weight) divided by volume.
  6. The heavy bar of pure gold and the pure gold ring have the same density.
  7. When you squeeze a loaf of bread, its mass does not change, but its volume does change - it gets smaller. This means that the density of the loaf gets larger. (Density = mass/volume)

last update February 6, 2006 by JL Stanbrough