1. Chemistry of Life
Biology Chapter 2

2. Elements
Substances that cannot be broken down chemically into simpler kinds of matter
More than 100 types
Organized on the periodic table of elements

3. Elements of Life Approximately 27 are essential to life
90% of mass of living things are O, C, H, N
Elements of Life: CHONPS
Remember the Elephants in the Element Song?

4. Atom
Smallest unit of an element that retains all the properties of that element

5. Nucleus Central region of an atom
Contains the bulk of the mass of the atom
Consists of protons and neutrons

6. Proton Positively charged particle Located in Nucleus
Mass approximately 1 AMU

7. Neutron Neutral charged particle, No Charge Located in Nucleus
Mass approximately 1 AMU

8. Electron Negatively charged particle
Orbits the nucleus in the electron cloud
Mass practically zero

9. Orbitals Electrons orbit in specific regions called orbitals-
3D space higher probability location of orbital
Each orbital is associated with an energy level
Electrons in orbitals further from the nucleus have more energy

10. Electron Orbitals & Energy Levels
Each orbital can hold 2 electrons
Each energy level consists of different #s of orbitals

11. Build an Atom

12. Atomic Number Number of protons in an atom Determines type of element
Elements are organized by atomic number on the periodic table
Atomic Number for Carbon is 6

14. Mass Number Total number of Protons + Neutrons
Protons have mass of 1 amu
Neutrons have mass of 1 amu
Mass Number – Atomic Number = # of neutrons

15. Mass Number

16. Compounds Made of atoms of two or more elements in fixed proportions
Chemical formula shows kinds and proportions of atoms
H2O -
C6H12O6 –
CO2-
CO -
O2- Compound?

17. Molecule
Simplest part of a substance that retains all properties of that substance
Can exist in a free state
Can be very large- carbohydrates, lipids, proteins, nucleic acids (macromolecules)
H2O -
C6H12O6 –
CO2-
CO -
O2-

18. Chemical Bonds Stable Atom = Highest energy level filled
Attractive forces that hold atoms together
Covalent Bonds
Ionic Bonds
Hydrogen Bonds
Stable Atom = Highest energy level filled

19. Valence Electrons
Number of electrons in the highest energy level for that atom
Atoms are more stable when outer energy level is full (2 or 8 electrons depending on element)

20. A groups are relatively easy to figure out the valence electrons- look at the group name
B groups are very fancy, d level orbitals that have many electrons at each energy level- learn more about this in chemistry

21. Dot Diagrams Show the valence electrons on an atom
Hydrogen and helium only hold up to 2 valence electrons
Other elements (that we will look at) hold up to 8 valence electrons

22. Covalent Bond Two atoms share one or more pairs of electrons

23. Ion Some atoms only need to gain or lose 1 or 2 electrons to be stable
Ions- Forms of an atom that have gained or lost electrons
Fills the outer shell of electrons
If electrons are gained, Ion is NEGATIVE (ANION)
If electrons are lost, Ion is POSITIVE (CATION)

24. Ion Example
Sodium and Chlorine

25. Ionic Bonding Atoms form ions and become positive or negative
Opposite charges attract