1. Chapter 2 Week 1 & 2 of Trimester 1
8/12/13
LEAP Bio 8th Grade

2. Chemicals are the stuff that make up
Our bodies
Bodies of other organisms
Physical environment

3. Life’s Chem is tied to water
Life 1st evolved in water
All living organisms require water
Chemical reactions in your body occur in cells consisting of 70% - 90% water

4. Elements, atoms, and Compounds

5. atoms
Smallest unit of matter that still retains property of an element

6. Element
Substance that cannot be broken down into other substances

7. Isotopes
Atoms of same element that differ in the number of neutrons that they contain
Different isotopes of an element have
- same # of protons
-different # of neutrons
Behave identically in chem reactions

8. Compound Substance consisting of 2+ different elements in fixed ratio
Organisms are composed of elements In combinations called compounds

9. Subatomic Particle Info
Protons and neutrons have same mass
Atomic number = number of protons
Atomic mass number = sum of protons and neutrons in nucleus

10. Compound
Substance consisting of two or more different elements in a fixed ratio
More common than pure elements
Molecule that contains at least 2 different element
All compounds are molecules

11. In radioactive isotopes the nucleus decays spontaneously giving off particles and energy

12. Elements that make up 96% of weight of living organisms
Oxygen
Carbon
Hydrogen
Nitrogen

13. Trace elements
Are essential
Only needed in small quantities

14. Chemical Bonds

15. notes
Of the three subatomic particles only electrons are directly involved in chemical activity
E occur in energy levels called electron shells
Distribution of electrons determines the atom’s chemical properties
# of e in outer shell determines chem prop of atom
Atoms whose outer shells are not filled tend to interact with other atoms and participate in chemical reactions

16. Distribution of e determines an atom’s chemical properties
Atoms with incomplete outer shells react so both atoms end up with completed outer shells
These atoms may react with each other by;
Sharing
Donating
Receiving e
These interactions result in atoms staying close together, held by attractions called chemical bonds

17. Covalent Bonds Strongest chemical bond
2 atoms share one+ outer shell e
2 or more atoms held together by covalent bonds form a molecule
Covalent bonds join atoms into molecules htrough e sharing
Atoms in covalent bond compete for shared e
Attraction for shared e is called electronegativity
More electronegative atoms pull harder

18. Polar Covalent Bond Unfair sharing of e Water molecules are polar
Oxygen has higher electronegativity than Hydrogen

19. Nonpolar Covalent bonds
In molecules of one element the pull toward each atom is =
Because each atom has same electronegativity

20. Ionic bonds Ion – atom/molecule with charge
2 ions with opposite charges attract each other
When attraction holds ions together it is called ionic bond
Salt is synonym for an ionic compound

21. Hydrogen Bonds
The charged regions on molecules are electrically attracted to oppositely charged regions neighboring molecules
Because the positively charged region is always a hydrogen atom the bond is called a hydrogen bond

22. Van Der Waals forces
When molecules are close together a slight attraction can develop between the oppositely charged regions of nearby molecules
Chemists call such intermolecular forces Van Der waals forces after the guy who discovered them
Not as strong as other bonds
Especially good at holding large molecules together

23. Chem reactions make and break chem bonds
Photosynthesis is a chem reaction
Co2 reacts with water
Sunlight powers conversion to produce the products glucose and oxygen
Remember that the structure of atoms and molecules determines how they behave

24. Water’s Life-Supporting Properties
Hydrogen bonds make liquid h2o cohesive
Cohesion – tendency of molecules of the same kind to stick together
It is much stronger for water than other liquids
Most plants depend on cohesion to help transport water and nutrients from their roots to their leaves
Adhesion - Tendency of 2 molecules to stick together

25. Water’s life supporting properties
Cohesion is related to surface tension – a measure of how difficult it is to break surface of a liquid
Hydrogen bonds give water high surface tension, making it behave as if it were coated with an invisible film
Water striders stand on water without breaking the water’s surface

26. Water’s hydrogen Bonds moderate temp
Because of hydrogen bonding water has the ability to resist temp change than other liquids
Heat = energy associated with movement of atoms and molecules in matter
Temperature = measures intensity of heat
Heat is released when hydrogen bonds form
Heat must be absorbed to break hydrogen bonds

27. When a substance evaporates the surface of the liquid that remains behind cools down in the process of Evaporate Cooling
This cooling occurs because the molecules with the greatest energy leave the surface
When water freezes each molecule forms stable hydrogen bonds with its neighbors
As ice crystals form the molecules are less densely packed than in liquid water

28. Water is less dense as a solid than a liquid because of hydrogen bonds (Ice floats)
Hydrogen bonds are stable in in ice

29. Water is the solvent of life
A solution is a liquid consisting of a uniform mixture of 2+ substances
Dissolving agent is solvent
Substance that is dissolved is solute
Aqueous solution is one in which water is the solvent

30. Water is the solvent of life
Water’s versatility as solvent results from the polarity of its molecules
Polar/charged solutes dissolve when water molecules surround them, forming aqueous solutions
Table salt is an ex of a solute that will go into solution in water

31. The chem of life is sensitive to acidic and basic conditions
In aqueous solutions a small % of water molecules break apart into ions
Some are hydrogen ions (H+)
Some are hydroxide ions (OH-)
Both are very reactive
Acid – compound that releases H+ to a solution
Base- compound that accepts H+

32. The ph scale determines how acidic or basic a solution is
0 = most acidic
14 = most basic
Each ph unit represents a tenfold change in concentration of H+
A buffer is a substance that minimizes change in ph
Accept H+ when it is in excess
Donates H+ when it is depleted

33. Acid precipitation
Sulfur and nitrous oxides react with water in air to form acids
These acids fall to earth as Acid precipitation which is rain, snow, or fog with a ph lower than 5.2

34. Ocean Acidification
CO2 dissolving in seawater lowers ocean ph in a process called Ocean Acidification

35. Need to know for quiz # 1 Quiz #1
I think this was the stuff to know for the very first quiz
Need to know for quiz # 1

36. Need to know for quiz
Describe importance of chem elements to living organisms
Explain formations of compounds
Describe atom structure
Distinguish btwn ionic, covalent, and hydrogen bonds
Define chem reaction and explain how it changes composition of matter

37. Need to know Describe importance of chem elements to living organisms
Explain formations of compounds
Describe atom structure
Distinguish btwn ionic, covalent, and hydrogen bonds
Define chem reaction and explain how it changes composition of matter
List/define life supporting properties of water
Explain ph scale