HOMEWORK for UNIT 2. Atoms

Atomic theory

1. Define the terms element, compound, and mixture. Illustrate your definitions with simple circle pictures.

2. Identify each of these circle pictures as pure element, pure compound, or mixture.

3. Using the symbols shown at right, draw circle pictures that depict

a. 4 atoms of pure B

b. A mixture of 3 A atoms and 2 B atoms

c. 3 molecules of pure AB

d. 2 molecules of pure A2B

e. a mixture of 1 molecule of A2, 2 molecules of B2, and 2 molecules of AB2

4. The drawing at right represents one molecule of CD. Draw circle pictures that

depict 4 molecules of CD

a. turning from liquid CD to gaseous CD

b. decomposing into C atoms and D atoms

Nuclear atom

5. a. How does the mass of a neutron compare to the mass of a proton?

b. How does the mass of an electron compare to the mass of a proton?

c. According to the nuclear model of the atom, how is mass distributed in the atom?

d. Compare the size of the nucleus to the size of the atom.

6. Complete this table of atoms. The symbol must include the mass number.

Symbol / Protons / Neutrons / Electrons / Atomic number / Mass number
34S
31 / 40 / 31
60 / 47
74 / 182
26 / 26 / 56

7. Argon has three naturally-occurring isotopes, with 18, 20, and 22 neutrons. Write the symbols for isotopes of argon.

8. List the number of protons & neutrons in the four naturally-occurring isotopes of chromium: 50Cr, 52Cr, 53Cr, and 54Cr.

Atomic mass

9. One atom of 12C has been assigned a mass of exactly 12 amu. What is the mass of one proton in amu? What is the mass of one neutron in amu?

10. Using an instrument called a mass spectrometer, it was found that atoms of element X were 2.25 times as heavy as atoms of 12C. What is the atomic mass of element X?

11. Copper has two naturally-occurring isotopes. 69.17% of naturally occurring copper is 63Cu (mass 62.9396 amu), and 30.83% is 65Cu (mass 64.9278 amu). What is the average atomic mass of Cu?

isotope / mass (amu) / abundance
Si-28 / 27.9769 / 92.2%
Si-29 / 28.9765 / 4.67%
Si-30 / 29.9737 / 3.10%

12. Silicon has three naturally-occurring isotopes, whose masses and abundances are shown in the table at right. Calculate the average atomic mass of Si.

Periodic table

13. Write these items into a blank periodic table:

a. the staircase that marks the boundary between metals and nonmetals

b. the metal, semi-metal (or metalloid), and nonmetal regions

c. alkali metals, alkaline earths, transition metals, halogens, and noble gases

d. the trends in atomic size across a period and down a group

e. period numbers and group numbers

14. Write the symbol for each element (some may have more than one possible answer):

a. period 3, group 4A d. period 6 alkali metal g. period 4 semi-metal (metalloid)

b. period 2, group 6Ae. period 5 halogenh. period 3 alkaline earth

c. period 1 noble gasf. the fifth transition metali. the element that does

in period 4 not belong to any family

15. Which is larger:

a. P or Clb. Kr or Xec. O or Cd. Rb or Na