1. Chemistry Refresher & Water
Mr. Perez

2. Before we begin, let’s see what you remember…
On the periodic table of elements, the number above the element’s abbreviation (atomic number) counts the number of _________ the element contains.
Electrons
Protons
Neutrons
Doughnuts
# of protons

3. Contd.
Carbon, hydrogen, oxygen and ____________ make up 96% of living matter.
Helium
Nitrogen
Boron
Potassium
Nitrogen

4. Contd.
____________ bonds are formed when two atoms share a pair of valence electrons.
Ionic
Hydrogen
Covalent
Double
Covalent

5. Contd.
TRUE or FALSE
If an element has 10 electrons, its electron distribution will have 2 electrons in the first valence shell and 8 in the second valence shell.
True

6. Matter & Elements
Organisms are composed of matter, or anything that takes up space and has mass
Matter is made up of elements, substances that cannot be broken down to other substances by chemical reactions

7. Compounds Sodium (Na) + Chlorine (Cl) = Table Salt (NaCl)
Compounds are made up of two or more elements and have characteristics different from the elements that make it up
Sodium (Na) + Chlorine (Cl) = Table Salt (NaCl)

8. Elements of Life
Carbon, Hydrogen, Oxygen, and Nitrogen make up 96% of living matter
REMEMBER: CHON = LIFE
The other 4% of living matter is made up of trace elements such as potassium, calcium, phosphorous and sulfur.

9. Structure of atoms Atoms are made up of:
The structure of atoms that makes up an element allows it to have certain properties
Atoms are the smallest units of matter that still retain the properties of an element
Atoms are made up of:
Protons (+) = atomic mass
Neutrons (0)
Electrons (-)

10. An Element’s Energy level
An element’s energy level depends on the distribution of valence electrons
Valence electrons are the electrons found in the outermost shell
Full shells are less reactive than those that are empty or missing a few electrons

11. Hydrogen 1H 2 He 4.00 Atomic number Helium 2He Mass number First shell
Figure 2.9
Hydrogen 1H 2 He
4.00
Atomic number
Helium
2He
Mass number
First
shell
Element symbol
Electron
distribution
diagram
Lithium
3Li
Beryllium
4Be
Boron 5B
Carbon 6C
Nitrogen 7N
Oxygen 8O
Fluorine 9F
Neon
10Ne
Second
shell
Sodium
11Na
Magnesium
12Mg
Aluminum
13Al
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Third
shell

12. Chemical Bonds
Atoms with incomplete valence shells can share or transfer electrons with other atoms
Chemical bonds keep them together
Covalent bonds involve the sharing of electrons
Single bonds is the sharing of one pair of electrons
Double bonds is the sharing of two pairs of electrons
Ionic bonds involve the loss or gain of an electron
Cation= + charged ion
Anion = - charged ion

13. Molecules
Molecules are formed by two or more atoms held together by covalent bonds
We use structural formulas to represent atoms that are bonded together
For example H—H, which can also be written H2
Compounds are formed when two or more different elements combine

14. Figure 2.12
Name and
Molecular
Formula
Electron
Distribution
Diagram
Lewis Dot
Structure and
Structural
Formula
Space-
Filling
Model
(a) Hydrogen (H2)
(b) Oxygen (O2)
(c) Water (H2O)
(d) Methane (CH4)

15. Weak chemical bonds STRONG = COVALENT WEAK = IONIC & HYDROGEN
These weak bonds help retain shapes

16. Hydrogen bonds
Hydrogen bonds are formed when a hydrogen atom is covalently bonded to an electronegative atom and is attracted to another electronegative atoms
Usually, the electronegative partners are oxygen or nitrogen
Electronegativity is an atom’s attraction for electrons in a covalent bond
The stronger the electronegativity the more electrons will be pulled to itself when sharing

17. Crash Course

18. Water, Water, Every Where!!!
Properties of Water
The Versatile Molecule

19. Expanding Upon Freezing
What if this did not occur?
Allows ice to float and stops lakes and rivers from freezing solid (insulation).

20. II. Water Molecule Water is made up of Hydrogen and Oxygen
Oxygen has 6 electrons and high electronegativity
Hydrogen has 1 electron and low negativity
Each water molecule has two polar covalent bonds, giving it partial positive and negative regions

21. II. Water Molecule C. This molecule H₂O is neutral (10 e⁻& 10 p⁺)
However there is more to this story...
D. Polarity: an uneven distribution of electrons between two atoms
1. Oxygen atom in water has a stronger attraction to the electrons than hydrogen
2. Water is a bent molecule so the oxygen end is slightly negative while the hydrogen end is slightly positive

22. III. Hydrogen Bond
A. Since polar molecules have a slightly charged end they are attracted one another
1. Slightly positive is written: (+)
2. Slightly negative is written: (-)
B. The bonding between the polar water molecules, from one oxygen to a hydrogen is a hydrogen bond
Hydrogen bonds are weak bonds but collectively together they are strong!

23. IV. Cohesion & Adhesion Adhesion Cohesion
A. The ability of water to form multiple hydrogen bonds gives it unique properties
1. Cohesion: attraction between molecules of the same substance
i.e. drops of water form beads on a flat surface (high surface tension)
2. Adhesion: attraction between molecules of a different substance
i.e. meniscus in a graduated cylinder and why water flows through a plant (capillary action)
Adhesion
Cohesion

25. V. Solutions & Suspensions
Water is not always pure
A. Mixture: material composed of two or more elements or compounds that are physically mixed together
i.e. salt water, salt & pepper, atmosphere
B. Two types of mixtures that can be made with water
Solutions: all components are evenly distributed
Suspensions: mixtures with nondissolved material and separate pieces

26. VI. Heat Capacity A. Water has a high specific heat.
In other words it takes a lot of energy to raise water just by 1 degree.
B. This allows organisms that not only live in water but others that are mostly made up of water to maintain a constant body temperature.

27. VII. Good Solvent
Because water is polar, it bonds to ions and polar molecules.
Even very small non-polar molecules, for example CO2 dissolve.
Remember, LIKE dissolves LIKE
Hydrophobic dissolved hydrophobic

28. Hydrogen Bonds & Pennies
Water molecules are polar because there is an uneven of electrons between the oxygen and hydrogen atoms. This causes one end of one water molecule to be attracted to another water molecule. This process is cohesion!
Lets test how strong these cohesion forces are by placing drops of water on a penny until the cohesive forces break
Hypothesis: If I place a max of ____ drops of water onto a penny, then the cohesive forces of water will break and water will spill onto the towel
Each person will conduct 2 trials and find the average.
What’s the IV, DV, Control?