Instructor’s Copy

Lab Worksheet – The Latest Trend

The data on this table depends on the property assigned.

Table 1: Scale data on ______(which property)

Scale information / # / Mass / MP / BP / Dens. / Radii / Ion / Elect
Length of soda straw (cm) 19.6
Half the straw length (cm) 9.8
Largest value of property to be investigated / 88 / 226 / 3620 / 4200 / 11.9 / 280 / 2372 / 4.0
Scale for straw length vs. property (cm):1/2 straw length /largest value of property / .11 / .04 / .003 / .002 / .82 / .035 / .004 / 2.45

Table 2: Trends on the periodic table

Property modeled / Trend down groups / Trend from left to right in period
Atomic number (# of protons) /

Increases going down

/ Increases going right
Atomic mass / Increases going down / Increases going right
Melting point / Except for hydrogen, decreases going down / Increases for first 4, then a major drop with continued decrease
Boiling point / Except for hydrogen, decreases going down / Increases for first 4 then decreases
Density / Except for sodium, increases going down / In general, it increases for the first 4, then a major drop with slight increases.
Atomic radius / Increases going down / Decreases going right until it reaches noble gas, which is bigger
Ionization energy / Decreases going down / Increases going right
Electronegativity / Decreases going down / Increases going right

QUESTIONS:

  1. What is the trend in atomic number? Using the idea that the atomic number is the number of protons, explain why this trend occurs.

The table is set up by increasing # of protons (atomic number).

  1. What is atomic mass? Explain why this trend occurs.

Atomic mass is the mass of the protons + neutrons. As the # of protons increases, so does the number of neutrons and electrons. This increases the mass.

  1. What is the trend in melting and boiling points? Explain why this might occur.

Both points decrease going down the groups because the elements

  1. What is density? Explain why this trend might occur.

Density is the mass/volume of a substance. It tells how tightly packed the atom is. In general, the density increases for the first 4 columns in a period because the mass increases while the volume does not change much. After the first 4, the volume decreases as the electrons are held slightly closer. Going down the group, the density generally increases as a large amount of mass is added to the nucleus.

  1. What is atomic radii? Explain why this trend might occur.

Half the distance from the center of the nucleus to the outer electrons. Radius increases going down the group as more energy levels are added to the atom. Radius decreases going right because the electrons are held closer to the nucleus as the energy level fills up.

  1. What is ionization energy? Explain why this trend is present.

Ionization energy is the energy needed to remove the most loosely held electron. This is directly related to radius, it decreases as the radius increases because the electrons are easier to pick off.

  1. What is electronegativity? Explain why this trend might occur.

A measure of the tendency of an atom to attract a bonding pair of electrons. As the atom gets bigger, it does not attract its own electrons so it cannot pick electrons off another atom.

  1. What is the relationship between electronegativity and ionization energy?

They are directly related. If the atom can’t hold its electrons to its nucleus, it can’t attract other electrons either.

  1. What is the relationship between atomic number and atomic mass?

Protons have mass. If the number of protons increases, the mass increases.

  1. What is the relationship between atomic radius and other properties on the table.

The atomic radius seems to directly affects the ionization energy and the electronegativity because the larger the atom, the less likely it is to hold its own electrons tightly or attract electrons from other atoms.