Question

activity b (continued from previous page)

1. interpret: select the atomic radius tab. what do you notice?
2. predict: on the atomic radius tab click clear. select the periodic table tab. elements in the same column of the periodic table are called chemical families, or groups. how do you think the size of atoms will change from top to bottom within a chemical family?
3. test: hydrogen, lithium, and sodium are all in the same chemical family. use the gizmo to find the atomic radius of each, and list them below.

hydrogen radius: ____ lithium radius: __ sodium radius: ____

1. analyze: how does the atomic radius change as you go from the top to the bottom of a chemical family?
2. challenge: think about the factors that control atomic radius and the patterns youve seen.

a. why does the atomic radius decrease as electrons are added to a shell?
b. why does the atomic radius increase as you go from the top to the bottom of a chemical family?

1. think and discuss: compare the electron configurations of hydrogen, lithium, and sodium. why do you think these elements are grouped in the same family?

Explanation:

Step1: Interpret atomic radius trends

When looking at the atomic - radius data, one may notice trends across periods and groups. In general, across a period (from left to right), the atomic radius decreases, and down a group (from top to bottom), the atomic radius increases.

Step2: Predict group - trend

As we move from top to bottom within a chemical family (group), the number of electron shells increases. Each new shell is farther from the nucleus, so we predict that the atomic radius will increase.

Step3: Test for specific elements

Hydrogen radius: 37 pm; Lithium radius: 152 pm; Sodium radius: 186 pm. (These values are approximate and can vary depending on the measurement method).

Step4: Analyze group - trend

As we go from the top to the bottom of a chemical family, the atomic radius increases. This is because with each successive element down a group, a new electron shell is added, increasing the distance between the outermost electrons and the nucleus.

Step5: Challenge - part A

When electrons are added to a shell, the effective nuclear charge increases. The protons in the nucleus attract the added electrons more strongly, pulling the electrons closer to the nucleus, thus decreasing the atomic radius.

Step6: Challenge - part B

As we go from the top to the bottom of a chemical family, new electron shells are added. Each new shell is farther from the nucleus, and the shielding effect of the inner - shell electrons reduces the effective nuclear charge on the outermost electrons. So, the outermost electrons are held less tightly, and the atomic radius increases.

Step7: Think and discuss

Hydrogen has an electron configuration of 1s¹, lithium has 1s²2s¹, and sodium has 1s²2s²2p⁶3s¹. They are grouped in the same family (Group 1, alkali metals) because they all have one valence electron in their outermost shell. This similar valence - electron configuration gives them similar chemical properties.

Answer:

1. Trends in atomic radius across periods and groups can be observed.
2. The atomic radius will increase from top to bottom within a chemical family.
3. Hydrogen radius: 37 pm; Lithium radius: 152 pm; Sodium radius: 186 pm
4. The atomic radius increases as we go from the top to the bottom of a chemical family.
5. A. The effective nuclear charge increases, pulling electrons closer. B. New electron shells are added, increasing the distance from the nucleus.
6. They all have one valence electron in their outermost shell, giving them similar chemical properties.