When writing electron confi gurations for elements in period 4, why are electrons placed in the 4s sublevel before the 3d sublevel?

List the four different sublevels. Given that only a maximum of two electrons can occupy an orbital, determine the maximum number of electrons that can exist in each sublevel.

Use the periodic table to give the number of electrons in the indicated sublevels for the 3d in manganese.

Consider the electron confi gurations of the noble gases. Which valence sublevels are completely fi lled for each noble gas?

Which is the larger ion, $S^{2-}$ or $Cl^-$ ? Explain.

For each pair, identify the larger atom or ion.
(a) F or $F^-$ (b) Sr or $Sr^{2+}$

Why are krypton atoms larger than argon atoms?

Rank the following elements in order of increasing atomic size: Mg, P, O.

Explain, in terms of ionization energies, why the following ions do not form under normal conditions.
(a) $Ba^{3+}$ (b) $O^{2+}$ (c) $Cl^+$

What does it mean when we say that photon energy is proportional to frequency?

Complete each sentence by writing the form of the verb indicated in parentheses.

The art students are _________ pictures of buildings. (present participle of sketch)

Solve the given problems.

The vertical cross-section of a culvert under a road is elliptical. The culvert is $18$ m wide and $12$ m high. Find an equation to represent the perimeter of the culvert with the origin at road level and $2.0$ m above the top of the culvert.

Complete of the following mini-dialogues by writing in the question that was asked.

(a qui / tu) - $\rule{5cm}{1pt}$

• J'ai téléphoné a ma cousine.

Complete each sentence by writing the form of the verb indicated in parentheses.

_________ anyone _________ my little brother? (present perfect of see)