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Covalent bonds

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.


Covalent bonding is the sharing of electrons between atoms.

Once two atoms bond, their behavior complete changes, for instance, water is made of hydrogen gas (which is very explosive) and oxygen gas (which makes almost everything else around it flammable) yet together they form water.

Consider mercury, sulfur, sodium, carbon, hydrogen, oxygen

By itself, mercury is poisonous, and sodium is explosive. Yet covalently bonded together in thiomersal, is a safe and very well-tested antiseptic and antifungal agent.

Some people believe that just because an element, by itself, is dangerous, that any molecular containing the element must also be dangerous, but that is not so.

The very process of combining atoms contently changes their properties completely.


Elements are not compounds thimerosal

Covalent bonding can occur :

Between two atoms of the same element

Between atoms of elements close to each other in the periodic table.

Between atoms that have similar electronegativities (affinities for electrons)

It mostly occurs in nonmetals.

Why does covalent bonding occur? When atoms meet, and their electron clouds overlap, they are unstable. So their electron clouds reconfigure into lower energy, more stable shapes. For common chemicals, most of the time, this produces an octet.

Remember that octets aren’t a law of nature; they’re “magic numberw. To learn more about octets, Lewis theory, and magic numbers, see: Lewis theory, Dot Diagrams and Magic Numbers

Example: Carbon does not form ionic bonds. Each has 4 valence electrons (half an octet.)
To form ionic bonds, Carbon molecules would have to either gain or lose 4 electrons. This is highly unfavorable (takes too much energy)  Takes less energy to share electrons.


How does bonding occur?

A hydrogen atom has 1 p+ and 1 e-

If 2 H atoms get close enough, then the e- from each H feels the attraction from the proton of the other H atom
(shown by double headed arrow below)

The attractions are not strong enough to pull the e- completely away from its own proton. But they are strong enough to pull the 2 atoms close enough together – so that the e- feel the attraction from both protons.

When the e- are attracted to and shared by both atoms, the individual H atoms have bonded : they are now the H2 molecule.

This is a covalent bond.

 Two or more atoms covalently bonded are called a molecule.

Once bonded, the H2 molecule is more stable than the individual H atoms.

Atoms bond until their outer energy levels are full

Each H atom now feels 2 e- in its first energy level.

For any atom, the first energy level only accommodates 2e-

So for H2, each atom’s outer energy level is full.

Atoms will covalently bond until their outer energy level is full.

Once the outer levels are full, additional atoms will not covalently bond to it, for 2 reasons:

• An e- from a new atom would have to join an atom in the H2 molecule on the next energy level, further from the nucleus – where it would not feel a strong enough attraction.

• An e- from a H atom already in the H2 molecule – and close to the nucleus – would need to move further away to share with the new atom.

Both of these possibilities would make the molecule less stable, and so would not happen.

Covalent bonding also happens in a water molecule.

they share electrons = forms a covalent bond

Hydrogen and fluorine bonding

only showing valence electrons

from http://chemwiki.ucdavis.edu/Organic_Chemistry/Fundamentals/Introduction_to_Organic_Chemistry


The Molecular Shape of You (Ed Sheeran Parody) | By A Capella Science, Tim Blais

A dot isn’t the best way to try to sum up how electrons come and go
They are the states of a matter field that follows and equation that Dirac wrote
The Schrodinger part of the whole equation will just lead
In sub-c when it expands
Now get that Coulomb and add it in with a proton
And watch them start to dance
As hydrogen it’s like

“Oh proton I feel your tug
Central potential dip down pulling on me
But I’m not falling in deep
No that would break uncertainty”

“Say oh
Electrons move too much
Slow down your pace and put that orbit on me
Come on now follow my lead
Come come on now follow my lead

Orbitals take the shape they do
As stable states of the quantum rules
And when a one approaches two
They combine and they’re bonding
Thus hydrogen as a rule
Is found in nature as H2
Energy configuring a molecule
Diatomically bonding

Low high low high low high low high
Diatomically bonding (x3)

Energy cofiguring a molecule
When orbitals take the shape they do

1/2 spin’ll give a lepton a twin
One up one down in the ground state
With S and P in quadruple degeneracy
The second shell can be filled up with eight
The higher angular powers spread out like beautiful flowers
In middle families they come into play
Well here’s a carbon with 6e
This ain’t nothing tricksy
But we’re gonna make some methane today
With hydrogen it’s like

“Oh atoms I feel your tug
Got my electrons bugged out pulling on me
Come on now settle round me
I’ll hybridize to sp3”

“Say oh
Carbon here’s touch
Spread out 109.47 degrees
Come on now follow our lead
Come come on now follow our lead”

Molecules take the shape they do
Combining states of the quantum rules
Like when a shell goes sp2
For sigma pi double bonding
And as widely as their purview
They spread out in the molecule
Look at benzene in a ring they hold it true
Aromatically bonding

Low high low high low high low high
Aromatically bonding (x3)

Look at benzene in a ring they hold it true
When orbitals take the shape they do

Come bond with me baby, come bond (x8)

Polymers take the shape they do
Combining base-level residues
Look they’re hydrogen bonding!
Peptides make a chain and group
In beta pleat sheets and corkscrews
With these secondary links they fold and move
They’re all over your body

Come bond with me baby, come bond (x6)

You’re a chemical machine
It’s best you knew
That molecules take the shape of you.

Copyright 2017 Tim Blais and A Capella Science
Original music by Ed Sheeran

Learning Standards

HS-PS1-1. Use the periodic table as a model to predict the relative properties of main group elements, including ionization energy and relative sizes of atoms and ions, based on the patterns of electrons in the outermost energy level of each element. Use the patterns of valence electron configurations, core charge, and Coulomb’s law to explain and predict general trends in ionization energies, relative sizes of atoms and ions, and reactivity of pure elements.

HS-PS1-2. Use the periodic table model to predict and design simple reactions that result in two main classes of binary compounds, ionic and molecular. Develop an explanation based on given observational data and the electronegativity model about the relative strengths of ionic or covalent bonds.

Benchmarks: American Association for the Advancement of Science.

The number of protons in the nucleus determines what an atom’s electron configuration can be and so defines the element. An atom’s electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons. 4D/H2*

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