BIO152H5 Chapter Notes - Chapter 2: Endergonic Reaction, Hydroxy Group, Heat Capacity
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Notes From Reading
CHAPTER 2: WATER AND CARBON: THE CHEMICAL BASIS (PGS. 19-44)
Key Concepts
- Molecules form when atoms bond to each other. Chemical bonds are based on electron
sharing. The degree of electron sharing varies from nonpolar covalent bonds, to polar
covalent bonds, to ionic bonds.
- Of all small molecules, water is the most important for life.
- Chemical reactions tend to be spontaneous if they lead to lower potential energy and higher
entropy.
- Most of the important compounds in organisms contain carbon.
Introduction
- Chemical Evolution – is the proposition that early in Earth’s history, simple chemical
compounds in the atmosphere and ocean combined to form larger, more complex
substances
2.1 The Building Blocks of Chemical Evolution
- Each element has a unique atomic number and contains a characteristic number of protons,
called the atomic number.
- The mass number (indicated in superscript) is the number of protons + neutrons of the most
common isotope.
- Elements commonly found in organisms have at least one unpaired valence electron. The
number of unpaired electrons in an atom is its valence.
Chemical Bonding
- Unfilled electron orbitals allow formation of chemical bonds, and atoms are most stable
when each electron orbital is filled.
- Covalent bond: Each atom’s unpaired electrons are shared by both nuclei to fill their
orbitals
- Nonpolar covalent bond: Electrons are evenly shared between two atoms and the bond
is symmetrical.
- Polar covalent bond: Electrons are asymmetrically shared
- Ionic bond: Electrons are transferred from one atom to another
Electronegativity of Atoms
- An atom in a molecule with a high electronegativity will hold the electrons more tightly and
have a partial negative charge (δ–), whereas the other atom will have a partial positive
charge (δ+).
- Cation: An atom that loses an electron and becomes positively charged.
- Anion: An atom that gains an electron and becomes negatively charged.
How Many Bonds Can an Atom Have?