CHEMISTRY BASICS The foundations of biology Elements and

CHEMISTRY BASICS The foundations of biology

Elements and Compounds � � � Organisms are composed of matter. Matter is composed of elements. Element = a substance that cannot be broken down to other substances by chemical reactions Elements combine in fixed ratios to form compounds. Compounds have properties that are different from their constituent elements. � Example: sodium (metal) + chlorine (poisonous gas) = sodium chloride (table salt)

Elements and Compounds � � Living matter is primarily composed of Carbon, Oxygen, Hydrogen, and Nitrogen. Trace elements are needed only in very small amounts.

Atomic Structure � � � Elements differ in their properties based upon their atomic structure. An atom is comprised of protons (+) and neutrons (neutral) packed together in a nucleus, and electrons (-) swarming around them. The mass of protons and neutrons is measured in amu’s (atomic mass units). *electron mass is negligible

Atomic Structure � � � Atomic Number = # of protons… unique to each element Atomic Mass = # of protons and neutrons When atomic symbol is written, the atomic number is written as a subscript and the atomic mass is written as a superscript on the left hand side of the element’s symbol. � Example:

Atomic Structure � � � Isotopes – different forms of an atom with differing numbers of neutrons. A mixture of isotopes exists in nature, but some are more plentiful and stable than others. Radioactive Isotope – an atom whose nucleus spontaneously decays, giving off particles and energy… This can result in the formation of a different element if protons are lost.

Atomic Structure � � Electrons are the participants in chemical reactions, and they reside in different energy levels within an atom. The further it is from the nucleus, the more potential energy an electron has When electrons gain energy (from light for example), they are “excited” and jump to a higher shell. When electrons lose energy, they fall down to a lower shell and release heat.

Atomic Structure � � Chemical behavior is largely determined by how many valence (outer shell) electrons an element has. 8 = stable/unreactive An “orbital” is the location an electron is most likely to be found. Unpaired electrons react.

Chemical Bonds � � Atoms that combine to form molecules and compounds both have unpaired electrons. Valence electrons are either… � Shared – Covalent bond Molecules: 2+ atoms held together Polar vs. Nonpolar (shared equally or unequally) � or Transferred – Ionic bond Anion: gained an electron Cation: lost an electron Ionic compounds = “salts”

“Bond Jokes”

Chemical Bonds � Weak bonds � Hydrogen – covalently bound H is attracted to another electronegative atom � Van der Waals – changing regions of positive and negative charge (due to moving electrons) that attract all atoms/molecules to each other � Molecular shape � Position of electron orbitals determines shape � Determines how molecules recognize and respond to one another (Structure relates to function. )

Chemical Reactions � � Definition = the making and breaking of chemical bonds leading to changes in composition of matter Reactants Products Chemical Equilibrium = the relative concentrations of reactant and product stabilize at a particular ratio. (Forward and reverse reaction rates are equal. ) Most chemical reactions are reversible.