Question

1. what trends do you notice for the atomic radii of group 2a?
2. what trends do you notice for the atomic radii of period 3?
3. explain why this trend occurs.
4. ionization energy is the amount of energy required to remove an electron from an element. using the ionization energies of the elements in period 2 listed below, make a line graph the values vs. atomic number.

element	ie (kj/mole)	element	ie (kj/mole)
be	900	o	1314
b	799	f	1682
c	1088	ne	2080

Explanation:

Question 2

Group 2A elements are alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra). As we move down Group 2A (increasing atomic number), the atomic radius increases. This is because each subsequent element has an additional electron shell. For example, Be has electron shells \(1s^2 2s^2\), Mg has \(1s^2 2s^2 2p^6 3s^2\) – the outermost electrons are in a shell further from the nucleus, so the radius is larger.

Period 3 elements are Na, Mg, Al, Si, P, S, Cl, Ar. As we move across Period 3 (from left to right, increasing atomic number), the atomic radius decreases. This is due to increasing nuclear charge (more protons) pulling the valence electrons closer to the nucleus, while the number of electron shells remains the same (all in the 3rd shell for Period 3).

For atomic radius trends:

• Down a group (e.g., Group 2A): Each element has an additional electron shell. The outermost electrons are farther from the nucleus, so atomic radius increases (shielding from inner shells reduces nuclear pull on outer electrons).
• Across a period (e.g., Period 3): Nuclear charge (\(Z\)) increases (more protons) while electron shells remain the same. The increased positive charge pulls valence electrons closer to the nucleus, decreasing atomic radius (shielding from inner electrons is constant across a period).

(Note: The question likely refers to the period trend from Q3, but the explanation applies to group/period trends generally.)

Answer:

As atomic number increases (moving down Group 2A), atomic radii increase.

Question 3