Covalent Bonds

What are covalent bonds?

Bonds which occur between two atoms with similar electronegativities such that the electrons are shared between both atoms, commonly between two non-metals. Molecular oxygen, O$_{2}$, is a good example of this:

Figure 30.2: The Covalent Bond: O$_{2}$

What is bond order?

Fancy scientific term for the number of electrons shared between two atoms.

What are the three general types of covalent bonds and how do the bond lengths and energies vary with the different types of bonds?

Table 30.1: Three general covalent bonds, bond lengths and bond energies.

Bond type ($e^{-}$ number)	Bond Length	Bond Energy
Single bonds (2 $e^{-}$)	Short	Low
Double bonds (4 $e^{-}$)	Shorter	Medium
Triple bonds (6 $e^{-}$)	Shortest	High

Bond energy basically means the energy required to break a bond. As we will see later in thermochemistry (and the law of conservation of energy), the energy to create something is equal to the energy required to break it. Therefore, ``bond energies'' are equivalent to the amount of energy to create or break a respective bond.

Figure 30.3: Single, double and triple covalent bonds.

What types of bonds can form when s and p orbitals overlap?

Sigma ($\sigma$) and pi ($\pi$).

What do sigma ($\sigma$) and pi ($\pi$) bonds look like?

$\sigma$- and $\pi$-bonds are seen below in Figure 30.4:

Figure 30.4: $\sigma$- and $\pi$-bonds. $\sigma$- bonds (left) are formed between two s orbitals (left, top), one s and one p (left, middle) or two p$_{x}$ orbitals (left, bottom). $\pi$- bonds (right) are formed between two p$_{y}$ or two p$_{z}$ orbitals; each would appear similarly and only one is depicted (right).

What are hybridized orbitals?

Concept that describes the mixing of s and p orbitals.

What are the three most common hybridized orbitals?

sp$^{3}$, sp$^{2}$ and sp orbitals: see Table 30.2 below:

Table 30.2: sp$^{3}$, sp$^{2}$ and sp orbitals.

	# of hybrid orbitals	Used Orbitals	Unused Orbitals
		$s$
$sp$	2	$p_{x}$
			$p_{y}$
			$p_{z}$
		$s$
$sp^{2}$	3	$p_{x}$
		$p_{y}$
			$p_{z}$
		$s$
$sp^{3}$	4	$p_{x}$
		$p_{y}$
		$p_{z}$

What hybridized orbital creates single bonds?

$sp^{3}$

What theory predicts the spacial configuration assumed by the atoms in a molecule?

Valence shell electron pair repulsion theory (VSEPR).

What are five key arrangements that you should be familiar with?

Figure 30.5: Five key bond arrangements: linear (a), trigonal planar (b), tetrahedral (c), trigonal bipyramidal (d), and octahedral (e).

What are the steps involved when predicting a molecule's arrangement given a formula, e.g. CH$_{4}$ or H$_{2}$O?

Figure 30.6: VSEPR: Lewis dot structures for CH$_{4}$ and H$_{2}$O.

Figure 30.7: VSEPR: lone pairs of electrons for CH$_{4}$ and H$_{2}$O.

Figure 30.8: VSEPR: most stable arrangement for CH$_{4}$ and H$_{2}$O.

Note: VSEPR treats bonding and non-bonding electron pairs equally and they can be considered as ``spherical objects''. Therefore, methane has four ``spherical objects'' corresponding to its four C-H bonds. Similarly, water also has four ``spherical objects'' corresponding to two H-O bonds and two pairs of non-bonding electrons. Ultimately, both have tetrahedral structures because of their electrons, but water appears bent because it only has two bonding pairs of electrons.