Covalent, Ionic, and Hydrogen Bonds

Introduction to Biology and Chemistry

Carbon is a relatively small atom with 6 protons and 6 neutrons (atomic weight of 12).
It can form rings, sheets, spirals, and double or triple bonds due to its size.
Carbon is "kind" because it's not as reactive as elements like fluorine, chlorine, or sodium.
Carbon needs four extra electrons and bonds with various molecules like hydrogen, oxygen, phosphorus, and nitrogen.
Life is based on carbon, so scientists have difficulty conceiving non-carbon-based life.

Atoms have electron shells and need them filled to be stable.
Carbon has 6 electrons: 2 fill the first shell, and 4 are in the second shell.
Carbon forms covalent bonds by sharing electrons with other atoms. Methane (CH_4) is an example where carbon shares four electrons with four hydrogen atoms.
Lewis dot structures represent how atoms bond together.

Gilbert Lewis created Lewis dot structures and also worked on Lewis acids and bases.
Nominated for the Nobel Prize 35 times but never won.
Coined the term "photon," revolutionized acid-base theories, produced the first molecule of heavy water, and conceptualized the covalent bond.
Elements react to achieve eight electrons in their outermost shell (octet rule).

Oxygen has six electrons and needs two, so it forms H_2O. (Water)
It can form two double bonds with carbon, creating CO_2 globally warming gas.
Nitrogen has five electrons; it bonds with three hydrogens to form ammonia (NH_3).
Amino groups consist of nitrogen bonded to two hydrogens.
Amino acids have an amino group bonded to a carbon that's bonded to a carboxylic acid group.

Non-polar covalent bonds: Electrons are shared equally (e.g., O_2).
Polar covalent bonds: Electrons are shared unequally, creating partial charges (e.g., water). Oxygen is more electronegative than hydrogen, thus has a slightly negative charge, and hydrogen has a slight positive charge.

Atoms transfer electrons to achieve a full octet, becoming ions.
Atoms generally prefer to be neutral but will sacrifice neutrality for a complete octet.

Sodium chloride (table salt) is an ionic compound.
Chlorine (halogen) needs one electron, and sodium (alkali metal) has one electron in its outer shell.
Sodium transfers its electron to chlorine, forming Na^+ and Cl^-. Opposite charges cause them to stick together forming an ionic bond.
Sodium and Chlorine can be very dangerous on their own, but together they are delicious.

Hydrogen bonds occur when hydrogen is bonded to a highly electronegative atom such as Oxygen.
Since water has a polar covalent bond, the hydrogen end is partially positive, and the oxygen end is partially negative.
Water molecules stick together due to hydrogen bonds.
Hydrogen bonds play an important role in proteins.