Biology 120 Notes (Part 2) Continuing the Discussion of Atoms and Other Molecules
Isotopes
- ==Isotopes== deal with neutrons in the atom.
- They differ in the number of neutrons.
- Some isotopes spontaneously decay and release radiation.
- Electrons are attracted to the nucleus; it takes energy to hold electrons in place.
- Electrons determine chemical behavior of atoms.
Valence Electrons
- The outermost energy shell is called the ==valence shell.==
- The ==octet rule== is a rule describing how a valence shell can only hold eight electrons (unless the atomic number is two or less.)
Molecules
- ==Molecules== are atoms held together by chemical bonds.
Chemical Bonds
- Molecular bonds contain energy.
- Valence shells determine the bonding activity.
- There are three types of covalent bonds which are called: ==ionic, covalent, and hydrogen.==
Ionic Bonds
- An ==ion== is a charged atom.
- An ==ionic bind== forms when electrons are transferred from one atom to another.
- Salts are sold substances that usually sperate and exist as individual ions in water.
- The first ring holds only two electrons
- After the second ring and as more rings are created, they will hold eight electrons each.
Covalent Bonds
- ==Covalent bonds== are a type of bond that describes how electrons are shared.
- Covalent bonds can either be polar or nonpolar.
Nonpolar and Polar Bonds
- Electrons are not always shared equally.
- Atoms may have different electronegativities.
- ==Electronegatives== describe the strength with which atoms pull electrons toward themselves.
- In general, when moving up to the right on the periodic table, the higher the electronegativity.
Hydrogen Bonds
- A ==hydrogen bond== is a weak attraction between a slightly positive hydrogen atom and a slightly negative tom in another molecule.