Live practice

Some central atoms have fewer than eight electrons, some species have an odd total electron count, and third-period or heavier atoms may exceed eight.

A noble gas combines very high ionisation enthalpy with positive electron-gain enthalpy (V). The smallest IE₁ marks the strongest metal (II); the most negative electron-gain value marks the strongest non-metal (III). Element VI has two relatively accessible electrons, while I has one valence electron but a very large IE₂ and corresponds to a small, polarising metal cation.

Shell n contains n² orbitals; each can contain one electron of a specified spin. An s subshell contains one orbital with two spins.

For multiplication and division, retain the least number of significant figures. An exact counting number does not limit precision. For addition, retain the least number of decimal places.

Translate every condition into an equation and retain exact values throughout the ellipse calculation.

The last line satisfies the original conditions and supplies every requested part.

Translate every condition into an equation and retain exact values throughout the straight-line calculation.

The last line satisfies the original conditions and supplies every requested part.

Every real number is either rational or irrational. Removing all rational numbers from \(\mathbb R\) therefore leaves precisely those reals that cannot be written as \(\frac{p}{q}\), where \(p,q\in\mathbb Z\) and \(q e0\).

\(I=2.5\times10^{-3}\) A.

\[\begin{aligned}f &= \frac{1}{P}\\&= \frac{1}{1.5}\\&= +0.667\end{aligned}\] m \(=+66.7\) cm. Positive focal length identifies a convex converging lens.