1. The Chemical Basis of Life
Chapter 4
The Chemical Basis of Life

2. Matter
All living things are made up of matter – anything that has mass and takes up space
Water, air, and your body are different substances but are all made up of matter

3. Mass vs Weight Mass – the amount of matter an object has
Weight – the amount of mass an object has plus the force of gravity

4. States of Matter Matter exists in 4 different states
Solid – definite shape and volume
Liquid – definite volume, not shape
Gas – no definite shape or volume
Plasma - high temperature ionized gas

5. Elements
Element – substance made up of the same type of atoms that can not be broken down chemically into a simpler kind of matter
25 elements are important to living things
4 make up 96% of the living matter in your body
Oxygen, Carbon, Hydrogen, Nitrogen

6. Trace elements – elements that make up less than
Trace elements – elements that make up less than .01 percent of body mass, but critical to health
Ex. 1.5 mg of Iodine each day – affects thyroid gland
.004% Iron – important for O2 in your blood

7. Compounds
Compound – substance containing 2 or more elements that are chemically combined in a fixed ratio
Ex. H2O
Physical and chemical properties differ between the elements that make up the compound and the compound itself
Ex. Oxygen and Hydrogen = gases
Combined = liquid

8. Atoms Atom – smallest possible particle of an element
Greek atomos = invisible
Nucleus – consists of protons and neutrons and makes up most of the mass of the atom
Proton – positively charged particle
Neutron – neutral; particle with no charge
Electron – high energy, negatively charged particle with little mass

9. Atoms
Orbital – 3D region around a nucleus that indicates the probable location of an electron
Each orbit holds a certain amount of electrons
1st orbit – 2 e
2nd orbit – 8 e
3rd orbit – 8 e (for the first 18 elements, then it can hold 18e)

10. Atoms
In order to be stable, an atom must have its outer orbit filled with electrons
Ex. He and Ne both have 8 e in their outer orbits
Atoms have the same number of protons (+) as electrons (-), therefore, an atom is neutral

11. Atoms
Bohr Models
Periodic Table – chart that summarizes and organizes the elements
Chemical symbol – letters
Atomic number – number of protons an atom has
Mass number – total number of protons + neutrons
Ex: F 9 protons 10 neutrons = 19 atomic mass
Chem Table

12. Bohr Models
Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it.
Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits.

13. Isotopes
Isotopes – atoms of the same element that have the same number of protons, but different number of neutrons
Radioactive Isotope – one in which the nucleus decays over time, giving off radiation in the form of matter and energy
Used in research and in medicine

14. Ionic Bonds
Ionic bond – the attractive force between oppositely charged ions which form when electrons are transferred from one atom to another
Ion – electrically charged atom or molecule
Ex. Na+Cl-

15. Covalent Bonding
Covalent bond – forms when two atoms share one or more pairs of electrons
Ex. Water
Oxygen 6 electrons needs two Hydrogen

16. Molecules Molecule – 2 or more atoms held together by a covalent bond
Ex. H20 or O2
Models of Molecules
Chemical formula - #’s and types of atoms
Structural formula – how the atoms are linked by bonds
Space filling model – 3-D model with colored spheres

17. Chemical Reactions
Chemical Reactions – breaking of old and formation of new chemical bonds resulting in a new substance
Reactants – starting materials for a rxn
Products – ending materials in a rxn

18. Acids, Bases, and pH H2O H+ + OH-
Hydroxide ion = OH- Hydronium ion = H+
Acid – solution with more H+
Ex. HCl
Base – solution with more OH-
Ex. NaOH

19. pH Scale
pH scale – scale range from 0-14 that describes how acidic or basic a solution is
0-6 acid 7 neutral base

20. Buffers
Buffer – substances that cause a solution to resist changes in pH
Important because the slightest change in pH can be harmful to organisms
Ex. Blood