The Chemistry of life Chapter 2

Atoms Terms: Matter- anything that has mass and takes up space Made up of ATOMS Atomic Structure at the core is a dense nucleus comprised of two subatomic particles protons (positively charged) neutrons (no associated charge) orbiting the nucleus is a cloud of another subatomic particles electrons (negatively charged Weight- pull of gravity on a substance Mass- amount of a substance

Atoms An atom can be characterized by the number of protons it has or by its overall mass Atomic number the number of protons in the nucleus atoms with the same atomic number exhibit the same chemical properties and are considered to belong to the same element Mass number the number of protons plus neutrons in the nucleus

Electrons Electrons determine the chemical behavior of atoms electrons have energy of position, called potential energy the field of energy around an atom is arranged as levels called electron shells

Electron Shells Each shell as a specific number of electrons it can hold. 1st shell holds 2 2nd and 3rd hold 8

Lewis Dot Structure Based on the above information, which elements are unreactive (stable, inert)? Are elements with an incompletly filled outer energy level likely to form bonds?

Practice: Lewis Dot Structure

Isotopes Isotopes- atoms that have the same number of protons but differ in the number of neutrons Ex. C14 & C12

Radioisotopic Dating Carbon Dating

Molecules Molecules are groups of atoms held together by energy Atoms are held together by chemical bonds Three types of bonds: Ionic Covalent Hydrogen

Ions Neutral atoms have and equal number of protons (+ charges) and electrons (-) charges Atoms that lose or gain electrons are called IONS.

Ionic Bonds Ionic bonds form when atoms are attracted by opposite charges Form between a metal and a nonmetal Electrons are transferred from one atom to another

Covalent bonds Covalent bonds – form between two atoms when they share electrons covalent bonds are stronger than ionic bonds

Polar covalent bonds in polar covalent bonds, one nucleus attracts the shared electrons more than another nucleus this attraction for electrons by a nucleus is called the atom’s electronegativity

Hydrogen Bonds Weak bonds Play an important role in biological molecules Stabilize the shapes of many biological molecules by causing certain parts of a molecule to be attracted to other parts.

Properties of Water Properties Heat Storage Ice Formation High Heat of Vaporization Cohesion High Polarity

Heat Storage Water molecules require a large input of energy to raise the temperature Hydrogen bonds absorb heat when they break and release heat when they form

Ice Formation Ice is less dense than water because the water molecules form a crystal like structure This structure is due to hydrogen bonds spacing the water molecules apart

High Heat of vaporization Water turns into vapor if the temperature is high enough. Every gram of water that evaporates from your skin removes 586 calories of heat from your body

Cohesion Water molecules are attracted to one another because of their polarity- cohesion Water molecules are also attracted to other polar molecules- adhesion

High polarity Water molecules are polar and therefore attract other polar molecules. Hydrophilic- water loving Molecules that are soluble in water are those that dissolve in water. Hydrophobic- water fearing Molecules that are insoluble in water are those that do not dissolve in water (nonpolar)

Water Ionizes The covalent bonds within water molecules sometimes break. H2O ↔ OH- + H+ Water Hydroxide Hydrogen

pH Hydrogen ion concentration may be expressed with the use of the pH scale. pH= “power of Hydrogen” Pure Water- neutral Hydrogen ion concentration is 10-7 pH= 7 Hydroxide ion concentration is 10-7 pH scale is logarithmic- a difference of 1on the pH scale represents 10 fold change in hydrogen ion concentration

Acids and Bases Bases Acids Substances that combine with hydrogen ions when dissolved in water Lowers the Hydrogen ion concentration pH values are greater than 7 Example- sodium hydroxide (NaOH) Acids Substances that dissociates in water to increase the hydrogen ion concentration pH values are less than 7 Example- Hydrochloric acid HCl- (stomach acid)

Buffers The pH of almost all living cells and the fluids surrounding the cells is fairly close to 7. (Ex. human blood has a pH of 7.4) Slight alterations in pH can disrupt the activity of cells How do organisms maintain this constant pH? Buffers Donate hydrogen ions when their concentration falls and taking them the solution when their concentration rises.