If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Carbon and hydrocarbons

The element carbon and why it's essential to life as we know it. Properties and bonding patterns of carbon atoms.


Carbon isn’t a difficult element to spot in your daily life. For instance, if you’ve used a pencil, you’ve seen carbon in its graphite form. Similarly, the charcoal briquettes on your barbeque are made out of carbon, and even the diamonds in a ring or necklace are a form of carbon (in this case, one that has been exposed to high temperature and pressure). What you may not realize, though, is that about 18% of your body (by weight) is also made of carbon. In fact, carbon atoms make up the backbone of many important molecules in your body, including proteins, DNA, RNA, sugars, and fats.
These complex biological molecules are often called macromolecules; they’re also classified as organic molecules, which simply means that they contain carbon atoms. (Notably, there are a few exceptions to this rule. For example, carbon dioxide and carbon monoxide contain carbon, but generally aren't considered to be organic.)

The bonding properties of carbon

Why is carbon so popular for making molecular backbones? Why don’t we instead use, say, oxygen for the same purpose? For one thing, carbon-carbon bonds are unusually strong, so carbon can form a stable, sturdy backbone for a large molecule. Perhaps more important, however, is carbon’s capacity for covalent bonding. Because a C atom can form covalent bonds to as many as four other atoms, it’s well suited to form the basic skeleton, or “backbone,” of a macromolecule.
As an analogy, imagine that you’re playing with a Tinker Toy® set and have connector wheels with either two or four holes. If you choose the connector wheel with four holes, you’ll be able to make more connections and build a complex structure more easily than if you choose the wheel with two holes. A carbon atom can bond with four other atoms and is like the four-hole wheel, while an oxygen atom, which can bond only to two, is like the two-hole wheel.
Carbon’s ability to form bonds with four other atoms goes back to its number and configuration of electrons. Carbon has an atomic number of six (meaning six protons, and six electrons as well in a neutral atom), so the first two electrons fill the inner shell and the remaining four are left in the second shell, which is the valence (outermost) shell. To achieve stability, carbon must find four more electrons to fill its outer shell, giving a total of eight and satisfying the octet rule. Carbon atoms may thus form bonds to as many as four other atoms. For example, in methane (CH4), carbon forms covalent bonds with four hydrogen atoms. Each bond corresponds to a pair of shared electrons (one from carbon and one from hydrogen), giving carbon the eight electrons it needs for a full outer shell.


Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. We often use hydrocarbons in our daily lives: for instance, the propane in a gas grill and the butane in a lighter are both hydrocarbons. They make good fuels because their covalent bonds store a large amount of energy, which is released when the molecules are burned (i.e., when they react with oxygen to form carbon dioxide and water).
Image of a methane molecule, showing its tetrahedral shape and the bond angle of 109.5 degrees for each H-C-H unit.
Image credit: OpenStax Biology.
Methane (CH4), the simplest hydrocarbon molecule, consists of a central carbon atom bonded to four hydrogen atoms. The carbon and the four hydrogen atoms form the vertices of a three-dimensional shape known as a tetrahedron, which has four triangular faces; because of this, methane is said to have a tetrahedral geometry. More generally, when a carbon atom is bonded to four other atoms, the molecule (or part of a molecule) will take on a tetrahedral shape similar to that of methane. This happens because the electron pairs that make up the bonds repel each other, and the shape that maximizes their distance from each other is a tetrahedron.
Most macromolecules are not classified as hydrocarbons, because they contain other atoms in addition to carbon and hydrogen, such as nitrogen, oxygen, and phosphorus. However, carbon chains with attached hydrogens are a key structural component of most macromolecules (even if they are interspersed with other atoms), so understanding the properties of hydrocarbons is important to understanding the behavior of macromolecules.

Want to join the conversation?

  • leaf green style avatar for user Kachinsky
    How do people actually look and measure the angles of bonds if we haven't actually seen an atom?
    (31 votes)
    Default Khan Academy avatar avatar for user
    • purple pi teal style avatar for user Michaela O'Connor
      I think it's just maths, based on the knowledge we already have. If a molecule has 4 hydrogens and 1 carbon (methane, as in the example above), and we know that electrons repel each other, then there's only one set of angles that allow those electrons to all be as far apart from one another as possible. The lower the number of electrons, the greater the angle, presumably.
      (49 votes)
  • male robot hal style avatar for user usbatlle
    is there a program in which a person can mix and match different elements together and see what compounds they come up with, what compounds they form. then when the compound is formed the program gives a backstory o how that compound is used throughout life
    (29 votes)
    Default Khan Academy avatar avatar for user
  • piceratops seed style avatar for user pimentel.nestor
    Why is oxygen electronegative?
    (11 votes)
    Default Khan Academy avatar avatar for user
    • leafers ultimate style avatar for user Anthonie
      Oxygen is electronegative because it only needs 2 electrons to complete it's valence shell. Instead of losing an electron (like sodium, in sodium chlorine), it simply attracts to those 2 electrons. The more a atom wants an electron, the more electronegative it is and visa versa.

      To imagine whats more electronegative, simply look at the periodic table. At the far bottom left to the top right is the scale for how electronegative an atom is. The closer to the bottom left, the less an atom is electronegative. Closer to the top right, the more electronegative the atom is.

      Hope this helps ;)~
      (28 votes)
  • aqualine ultimate style avatar for user 16sylvia.wright
    If the bonds in methane are repelled to each other, then wouldn't the bonds be too far apart that it would break the bonds?
    (6 votes)
    Default Khan Academy avatar avatar for user
    • piceratops ultimate style avatar for user Darmon
      The force that repels the pairs of electrons in the bonds in not as strong as the force that attract the electron to the protons of the carbon and hydrogen atoms. Thus, the best the electron bonds can do to stay away from each other is to form a tetrahedron. :)
      (15 votes)
  • blobby green style avatar for user Ana Guidolin
    How do people die?
    (6 votes)
    Default Khan Academy avatar avatar for user
    • mr pink red style avatar for user DMS_HK
      People can die from various causes, and the scientific study of death is known as thanatology. Some common scientific explanations for death include:

      1. Cardiovascular events: Heart attacks, strokes, or other conditions that disrupt blood flow to vital organs can lead to death.

      2. Respiratory failure: Illnesses such as pneumonia, chronic obstructive pulmonary disease (COPD), or severe asthma can result in the inability to breathe properly, leading to death.

      3. Infections: Bacterial, viral, or fungal infections can overwhelm the body's immune system, causing organ failure and ultimately leading to death.

      4. Trauma: Severe injuries, including those from accidents, falls, or violence, can damage vital organs and cause death.

      5. Cancer: Uncontrolled growth of abnormal cells can invade and destroy healthy tissue, impairing essential bodily functions and eventually leading to death if left untreated.

      6. Neurological disorders: Conditions like Alzheimer's disease, Parkinson's disease, or amyotrophic lateral sclerosis (ALS) can progressively affect the brain and nervous system, leading to death.

      7. Organ failure: When one or more vital organs, such as the heart, liver, kidneys, or lungs, stop functioning properly, it can result in death if not treated or replaced through transplantation.

      8. Metabolic disorders: Conditions like diabetes, kidney failure, or liver disease can disrupt the body's normal metabolic processes, leading to complications that can be fatal.

      It is important to note that this list is not exhaustive, and each case of death is unique. Scientists and healthcare professionals continually study different aspects of death to better understand its causes and find ways to prevent or treat the underlying conditions.
      (15 votes)
  • piceratops seedling style avatar for user Atharva.nigoskar
    Is it possible to artificially create diamond using huge hydraulic presses with super hot base plates such that all conditions to create diamond are fulfilled ?
    (8 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user Sunnysidedown
    Here it says that carbon can bond with 4 other atoms because it has 4 electrons on its outermost shell, while oxygen can bond with only 2 but yhe outermost shell has 6 electrons why can't it bond with 6 atoms.
    (6 votes)
    Default Khan Academy avatar avatar for user
    • blobby green style avatar for user Kaitlyn
      The octet rule means that atoms tend to prefer having eight electrons in the outside valence shell. Since carbon has 4 valence electrons, it can bond with 4 hydrogen atoms (that have 1 valence electron) to reach the preferred 8 valence electrons. Since oxygen has 6 valence electrons, it only needs to bond with 2 hydrogen atoms in order to reach the preferred 8 valence electrons.
      (8 votes)
  • marcimus pink style avatar for user Crystal Fewtrell
    Why are hydrocarbons like methane, butane and propane considered to be organic macromolecules but not carbon dioxide or carbon monoxide?
    (9 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user jellybean
    why can't the hydrocarbons and the macromolecules separate from each other?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • piceratops sapling style avatar for user Lee MinJu
    What is a carbon monoxide and what does it do?
    (3 votes)
    Default Khan Academy avatar avatar for user