1. The Chemistry of life
Chapter 2

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

4. 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

5. 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

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

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?

9. Practice: Lewis Dot Structure

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

11. Radioisotopic Dating
Carbon Dating

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

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

14. 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

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

16. 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

17. 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.

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

19. 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

20. 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

21. 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

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

23. 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)

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

25. 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 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

26. 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)

27. 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.