General Chemistry in Biology

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Elements are substances that cannot be broken down into other substances by chemical means.

• There are 92 known naturally occurring elements in the world.
• Compounds are substances composed of two or more different elements in a fixed ratio
• An example is salt
• The smallest particle of an element is known as the atom     
• An atom consists of:
• Electrons
• These are negatively charged particles
• They are located outside the nucleus
• The arrangement of electrons are mostly in open space
• An orbital is the volume of space that electrons will be found in for 90% of the time
• 1st energy level: 2 electrons
• 2nd energy level: 8 electrons
• 3rd energy level: 8 electrons (up to element 20)
• Changes in the number of electrons will help determine chemical properties or behaviors of chemical reactions
• Neutrons
• Neutrons have no charge
• Located in the nucleus of an atom
• The neutron will help determine the atomic mass
• Neutrons can determine isotopes
• Isotopes are caused by the change in the number of neutrons that are found in the element.
• An isotope element will have a different mass
• Many isotopes are radioactive
• Isotopes can be used for radioactive dating or as tracers
• Protons
• Protons are positively charged particles
• Protons are located in the atomic nucleus
• Protons help determine the element, by providing the atomic number.

Atomic Number

• The atomic number will tell us the number of protons and even electrons, assuming that the atom is neutral in electrical charge

Atomic Mass

• Atomic mass is the sum of the protons and neutrons that found in the atomic nucleus.

Bonds and Molecules

• Chemical bonds are the forces between the interaction of elements, consisting of two or more atoms.
• Two basic types
• Covalent
• Bonds that form when pairs of electrons are shared between atoms
• Nonpolar covalent bonds
• Electrons are equally shared
• O2
• Polar covalent bonds
• Electrons are not equally shared
• H2O
• Ionic
• Electrons from one atom that are donated or completely transferred to another atom
• There is a gain or loss of electrons
• Anions: overall negative charge
• Gained at least one electron
• Cations: overall positive charge
• Lost at least one electron
• Example: CaCl2

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