In a helium atom, which contains two electrons, do you think that on average the electrons are closer to the nucleus or farther away than in a hydrogen atom? Why?

An oxygen isotope, ${ }_{8}^{16} \mathrm{O}$, has a nuclear mass of 15.994915 u. a. What is the mass defect of this isotope? b. What is the binding energy of its nucleus?

Thorium-231 is the product of alpha emission. It is radioactive and emits beta radiation. Determine (a) the parent nucleus of Th-231. (b) the daughter product of Th-231 decay.

Suppose an organism usually has 24 chromosomes in its nucleus. How many chromatids would it have just after the $S$ phase of the cell cycle?

Show that the magnetic dipole moment M of an electron orbiting the proton nucleus of a hydrogen atom is related to the orbital momentum $L$ of the electron by

$$M=\frac{e}{2 m} L.$$

How many protons and how many neutrons are there in a nucleus of
(a) neon, $76 \mathrm{Ne}$
(b) zinc, 557 ( $\mathrm{Z}$
(c) silver, ${ }^{10} \mathrm{Ag}$.

Positive and negative charges are attracted to one another. Which of the following are attracted to a negative charge: an electron, a proton, a neutron, a nucleus, an atom? Explain your thinking.

The element oxygen has three naturally occurring isotopes, with 8, 9, and 10 neutrons in the nucleus, respectively. Write the full chemical symbols for these three isotopes.

Describe how eukaryotic cells are able to keep such large amounts of DNA in the small volume of the cell nucleus. (Hint Review the structure of a chromosome in Chapter 10.)

The two ions $K^+}and $Ca^{2+}$ each have 18 electrons surrounding the nucleus. Which would you expect to have the smaller radius? Why?

Consider the beta decay ${ }^{10} \mathrm{Be} \rightarrow{ }^{10} \mathrm{~B}+\beta^{-}$, with the beryllium nucleus initially at rest. (c) What are the possible energies of that other particle?

Near the surface of the nucleus of a lead atom, the electric field has a strength of $3.4 \times 10^{21} \mathrm{~V} / \mathrm{m}$. What is the energy density in this field?

A nucleus of 4 neutrons and 4 protons that is surrounded by 2 orbiting electrons is

(a) a positive ion.

(b) a negative ion.

(c ) an alpha particle

(d) a beta particle

Give the number of protons and number of neutrons in the nucleus of each the following: (16.1) a. sodium-25 b. nickel-61 c. rubidium- 84 d. silver-110