1.

What is the number of electrons, protons and neutrons in an atom of radon-224?

Answer:

There are 86 protons in the radon nucleus. You determine this by looking for Rn in the periodic table and reading the atomic number for Rn.

 

There are 86 electrons in a neutral radon atom because the 86 positive protons must have 86 negative electrons to bring the total charge to zero.

 

The number of neutrons equals the mass number(224) minus the atomic number (86)

Number neutrons = 224 - 86 = 138.

2.

Copper has two naturally occurring isotopes. What is the average atomic mass for copper? Use the percent abundances and masses given here.

Isotope---------------------------------------	percent abundance	mass in amu
copper-63------------------------------------	69.09%----------------------------	62.93 amu----------------------------
copper-65	30.91%	64.93 amu

Answer:

The average atomic mass for copper is 63.546 amu in the periodic table Average = [ 69.09 / 100.00] [62.93 amu] + [30.91% / 100.00] [64.93 amu] Average = 43.478 amu + 20.069 amu = 63.547 amu Average = 63.55 amu rounded to four significant figures

 

 

3.

Locate the following on the outline of a periodic table.

a. alkali metals  Answer: Alkali metals are the elements Li, Na, K, Rb, Cs, Fr in Group 1A.

 

b. halogens       Answer: Halogens are the elements F, Cl, Br, I and At in Group 7A

 

c. elements with ns²np³ set of outer electrons

 

Answer: The representative elements in Group 5A N, P, As, Sb, and Bi have five outer electrons with the subshell ns²np³.

4.

Write the electron configuration for an atom with 17 electrons. Mark the valence electrons. What is the identity and group for this element?

Answer:

Chlorine, Cl, is an atom with 17 electrons.

 

Chlorine is in Group 7A and is one of the halogens.

 

 

The electron configuration for chlorine is 1s²2s²2p⁶3s²3p⁵.

 

The valence electrons are seven in the 3s²3p⁵ subshells. Chlorine is an example of a p-block element. The last electron is in the "3p" subshell.

5.

Sketch an atom of beryllium-9. Indicate the number of neutrons and protons in the nucleus. Show the relative average distances out from the nucleus for the electron subshells. Identify the valence electrons. Tell whether or not this element is an s-block element.

Answer:

Beryllium, Be, has atomic number 4. It has four(4 ) protons and four(4) electrons. The Be-9 isotope has 5 neutrons, ( neutrons = mass number - atomic number; neutrons = 9 -4 = 5) The electron configuration for beryllium is 1s22s2. The valence electrons are the two in the 2s2 subshell. The relative average distance for a shell is determined on average by the values for "n". The higher the quantum number "n" the greater the distance between the nucleus and the electrons in the shell. this was illustrated in the lectures when the 1s, 2s, 3s orbitals were discussed. Beryllium is an s-block element because the last electron is in the 2s subshell. All s-block elements have the outermost electrons (valence electrons) in an "s" subshell. The elements in Groups 1A and 2A of the periodic table are s-block.