PowerPoint by Kim Foglia Division High School Levittown, NY Modified by Kathleen Crawford Science Hill High School Johnson City, TN

The Chemistry of Life Domains of Study Domain of BioMolecules Domain of Cells Domain of Organisms Domain of Populations Domain of Communities IB Biology

I. Why are we studying chemistry? Chemistry is the foundation of biology.

Everything is made of matter Matter is made of atoms Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons Proton + Neutron Electron –

The World of Elements Different kinds of atoms =different elements H C Na Mg P S K Ca Different kinds of atoms =different elements

II. About 25 elements are essential for life Four elements make up 96% of living matter: • carbon (C) • hydrogen (H) • oxygen (O) • nitrogen (N) III. Five additional elements are important in living things: • phosphorus (P) • calcium (Ca) • sulfur (S) • iron (Fe) sodium (Na)

IV. Role of some elements in living things: Sulfur – Used in some amino acids Calcium – Found in bones/teeth Iron – Found in haemoglobin (hemoglobin) in animals Sodium – Needed for a nerve impulse Phosphorus – Found in cell membrane structures

V. Bonding properties Effect of electrons Electrons determine chemical behavior of an atom. Depends on number of electrons in atom’s outermost shell or energy level. Valence shell is another name for outer shell. How does this atom behave?

Bonding properties Effect of electrons What’s the magic number? Bonding properties Effect of electrons Atoms are stable when outer shell is full or has 8 electrons (Octet rule) Sulfur on the LEFT Magnesium on the RIGHT How does this atom behave? How does this atom behave?

VI. Elements & their valence shells Elements in the same row have the same number of energy levels. Moving from left to right, each element has a sequential addition of electrons (and protons)

Elements & their valence shells Elements in the same column have the same valence and similar chemical properties Remember some food chains were built on reducing O to H2O & some on reducing S to H2S Oxygen has medium electronegativity so doesn’t pull electrons all the way off hydrogen whereas chlorine would. So oxygen forms a polar covalent bond. Carbon has only a weak electronegativity so forms a nonpolar covalent bond

VII. Chemical reactivity Atoms tend to complete a partially filled valence shell or empty a partially filled valence shell This tendency drives chemical reactions… and creates chemical bonds – –

Weak bonds Strong bonds VIII. Bonds in Biology Hydrogen bond H2O Weak bonds hydrogen bonds attraction between + and – hydrophobic & hydrophilic interactions van derWaals forces ionic bonds (sometimes weak) Strong bonds covalent bonds- share electrons ionic bonds - transfer electrons; (sometimes strong)

Covalent bonds Why is this a strong bond? Forms molecules Two atoms share a pair of electrons Both atoms holding onto the electrons Very stable Forms molecules H Oxygen – H O H — H H2 (hydrogen gas) H2O (water)

Multiple covalent bonds 2 atoms can share >1 pair of electrons double bonds 2 pairs of electrons triple bonds 3 pairs of electrons Very strong bonds More is better! H H–C–H –

Polar covalent bonds Pair of electrons shared unequally by 2 atoms Water = O + H Oxygen has stronger “attraction” for the electrons than hydrogen Oxygen has high electronegativity Water is a polar molecule “+” and “–” poles Leads to many interesting properties of water… + – H Oxygen – – – +

Hydrogen bonding Polar water creates molecular attractions Weak bond Positive H atom in one water molecule is attracted to negative O in another water molecule. Also can occur wherever an -OH exists in a larger molecule. Weak bond Typical strength of 5.0 kcal/mol, but it varies. APBio/TOPICS/Biochemistry/MoviesAP/03_02WaterStructure_A.swf Weak bonds are still important!

Oxygen – Significantly larger nucleus Greater charge (+8) Hydrogen – Smaller nucleus Charge of (+1) Electron pair found closer to the oxygen nucleus than the hydrogen nucleus. Oxygen carries a small negative dipole, and hydrogen carries a small positive dipole.