Unit 2 Chemistry: Bonding, Ionic and Covalent Structures, and Properties

Flashcards covering photoelectron spectroscopy, ionic lattice structures, metallic bonding, alloys, covalent bonding, sigma/pi bonds, and potential energy diagrams.

In photoelectron spectroscopy (PES), what do the different peaks and the height of each peak represent?

Different peaks represent different orbitals ($1s$, $2s$, $2p$, $3s$), and the height of a peak represents the number of electrons in that orbital.

In a photoelectron spectroscopy plot with an inverted $x$-axis, what does a peak positioned further to the right indicate?

It indicates that the electrons are further from the nucleus.

Why do ionic compounds form crystal lattice structures instead of individual molecules?

They form lattice structures to maximize the attraction of opposite charges and reduce the repulsion between like charges.

What is the correct chemical formula for Magnesium Nitride formed from $\text{Mg}^{2+}$ and $\text{N}^{3-}$ ions?

$$\text{Mg}_3\text{N}_2$$

What is lattice energy, and how does a higher lattice energy affect a compound's melting point and solubility?

Lattice energy is the energy required to dissociate a solid lattice structure into gaseous ions. A higher lattice energy results in a higher melting point and lower solubility in water.

Why are solid ionic compounds brittle and non-conductive?

They are brittle because attempting to move the ions causes like-charge repulsion that breaks the crystal. They are non-conductive in the solid state because the ions cannot move freely (unless dissolved in water).

What atomic structure characterizes metallic compounds, and what physical characteristics does this structure produce?

Metals consist of ionic cores surrounded by a delocalized "sea of electrons." This structure makes them conductive, malleable, and shiny/lustrous, with high melting points.

According to the lecture notes, what metal combinations form steel/cast iron, bronze, and brass?

Steel/cast iron is carbon and iron; bronze is copper and tin; brass is copper and zinc.

How do substitutional alloys and interstitial alloys differ structurally?

Substitutional alloys consist of metals with similar atomic radii where one metal's atoms occupy the same lattice sites as the other. Interstitial alloys feature smaller atoms occupying the spaces in between the metal atoms.

What happens to the potential energy as two nonmetal atoms approach each other to form a covalent bond?

The potential energy goes down as the atoms approach until it reaches a minimum (the most stable bond distance), and then increases sharply if they get too close.

What is a sigma ($\sigma$) bond, and what conditions are required for orbitals to form one?

A sigma bond is formed by orbitals overlapping directly in the plane between the atoms. Conditions require that the atomic orbitals overlap and each orbital contains 1 unpaired electron (orbitals with 2 paired electrons cannot overlap).

What is a pi ($\pi$) bond, and which type of orbital can form it?

A pi bond occurs when orbitals overlap in the plane above and below the atoms (used when a sigma bond already exists), and only $p$ orbitals can form pi bonds.

How do bond order, bond length, and bond strength relate to one another?

Higher bond order (sharing more electron pairs) leads to shorter bond length and higher bond strength.

On a potential energy curve relative to internuclear distance, how do strong vs. weak bonds and shorter vs. longer bond lengths shift the graph?

Stronger bonds shift the potential energy curve down (lower energy), weaker bonds shift up, shorter bond distances shift to the left, and longer bond distances shift to the right.