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1. Chapter 2 - Chemistry

2. All Matter is Composed of
Atoms
Electrons
Protons
Neutrons

3. Atoms have Volume and Mass
Mass of one proton
or one neutron = 1 dalton (Da)
Mass of one electron = 9 × 10–28
(usually ignored).

4. Elements
Element: pure substance containing only
one kind of atom.
Elements are arranged in the periodic
table.
Each element has a unique chemical
symbol.

5. The Periodic Table

6. Periodic Table

7. The Periodic Table
98 % of living organisms are
made up of C, H, N, O, S, P

8. Isotopes
Some isotopes are unstable:
Radioisotopes give off
energy in the form of alpha,
beta, and gamma radiation
from the nucleus.

9. Electrons
The number of electrons determines how
atoms will interact.
Chemical reactions involve changes in
the distribution of electrons between
atoms.

10. Orbital Theory
Locations of electrons in
an atom are described by
orbitals.
Orbital: region where
electron is found at least
90% of the time.
Orbitals have
characteristic shapes
and orientations, and can
be occupied by two
electrons.
Orbitals are filled in a
specific sequence.

11. Orbital Theory
Orbitals occur in a series called electron shells or
energy levels.
First shell: one s orbital (holds 2 electrons)
Second shell: 1 s and 3 p orbitals (holds 8
electrons)
Additional shells: 4 orbitals (8 electrons)
Octet Rule!

12. So how does Orbital Theory work?
Fill electrons from the inside out.
The outermost energy shell is called the
Valence Shell

13. How Do Atoms Bond to Form
Molecules?
Chemical bond: attractive force that
links atoms together to form
molecules.
Valence shells of each atom interact

15. Covalent Bonds
Atoms share
one or more
pairs of
electrons, so
that the outer
shells are filled.
Strongest Bonds
(takes a lot of energy to
break)

16. Compound: a
molecule made up
of two or more
elements bonded
together in a fixed
ratio.
The molecular
weight of a
compound is the
sum of the atomic
weights of all
atoms in the
molecule.

17. Element Usual # of
Covalent Bonds
Hydrogen (H) 1
Oxygen (O) 2
Sulfur (S) 2
Nitrogen (N) 3
Carbon (C) 4
Phosphorus (P) 5

18. Types of Covalent Bonds
Covalent bonds can be
• Single—sharing 1 pair of electrons
• Double—sharing 2 pairs of electrons
• Triple—sharing 3 pairs of electrons

19. Electronegativity
Sharing of electrons in a covalent bond
is not always equal.
Electronegativity: the attractive force
that an atomic nucleus exerts on
electrons.

20. Element Electronegativity
Oxygen (O) 3.5
Chlorine (Cl) 3.1
Nitrogen (N) 3.0
Carbon (C) 2.5
Phosphorus (P) 2.1
Hydrogen (H) 2.1
Sodium (Na) 0.9
Potassium (K) 0.8
Electronegativity Video

21. Polar / Non-polar Covalent Bonds
• A polar covalent bond results when
electrons are drawn to one nucleus
more than to the other, because one
atom has more electronegativity
What type of
polar
molecule
Is this?
• What about a non-polar covalent bond?

22. Ionic Bonds
When one atom is much more electronegative
than the other, a complete transfer of
electrons may occur.
This results in two ions with fully paired
electrons in their outer shells. (Not an ionic bond!)

23. Ionic Bonds
• The charged ions the interact to form
an ionic bond
• Opposites attract…

24. Ions
Ions: electrically charged particles—
when atoms lose or gain electrons
Cations—positive
Anions—negative
Ionic bonds are formed by the electrical
attraction of positive and negative ions.
Salts are ionically bonded compounds.

25. Water is a polar compound
which can dissolve a salt

26. Hydrogen Bonds
Hydrogen bonds:
attraction between
the δ– end of one
molecule and the δ+
hydrogen end of
another molecule.
Water/DNA/Proteins

27. Hydrophobic Interactions
Polar molecules that form
hydrogen bonds with water
are hydrophylic (“water-
loving”).
Nonpolar molecules such
as hydrocarbons that
interact with each other,
but not with water, are
hydrophobic
(“water-hating”).

28. van der Waals forces
van der Waals forces: attractions between
nonpolar molecules that are close
together.
Individual interactions are brief and weak,
but summed over a large molecule, can be
substantial.

29. Chemical Reactions
Occur when atoms collide with enough
energy to combine or change their
bonding partners.

30. Water has a unique structure which
allows it to have “Special Properties”
- Polar molecule
- Forms hydrogen bonds
- Tetrahedral shape

31. Phase Shift of Water
• Latent Heat – heat
given off or
absorbed during
phase change
www.piercecollege.com/offices/weather/water.html

32. Special Properties of Water:
Ice Floats
– Less Dense
– Most Stable
(lower energy state)
Environmental
Significant?
• Oceans
• Horticulture

33. Special Properties of Water:
Heat Capacity
Heat Storage
Water has high specific
heat:
the amount of heat
energy required to
raise the temperature
of 1 gram of water by
1°C.
http://sci.gallaudet.edu/strait.gif
Environmental
Significance?

34. Special Properties of Water:
Evaporational Cooling
Heat of Vaporization (Latent)
• Uses Energy to break H-bonds
• Energy is absorbed during the transition from
liquid to water vapor
Environmental Significance?

35. Special Properties of Water:
Cohesion
In liquid 3.4 H-
bonds at all times
Environmental
Significance
– Surface Tension
– Transpiration

36. Aqueous Solutions
A solution is a substance (solute)
dissolved in a liquid (solvent).
Acids/Bases
Buffers

37. Acids and Bases
+ −
HCl → H + Cl
Acids: dissolve in water
Strong Acid
and release hydrogen
ions: H+ (protons). − COOH → −COOH − + H +
Weak Acid
NaOH → Na + + OH −
Bases: accept H+ ions.
Strong Base
− +
OH + H → H 2O −
HCO3 + H + → H 2CO3
Weak Base
Reduces H +

38. Is water an acid or a base?
+ −
H 2O → H + OH
• Water acts as both a weak acid and a
weak base.
• Water has a slight tendency to ionize.

39. pH
pH = negative log of the
molar concentration of H+
ions.
pH = − log H [ ] +
H+ concentration of
purewater is 10–7 M
pH = 7.
10–7 [H+] + 10–7 [OH-] = 10–14
Lower pH numbers mean
higher H+ concentration, or
greater acidity.

40. pH Questions
• If the pH of a • If a solution has a
solution was 2. [ H+]=10-5
– [ H+]=? – pH=?
– [OH-]=? – [OH-]=?

41. Buffers
Living organisms +
HCO3 + H ⇔ H 2CO3
maintain constant
internal conditions
(homeostasis).
Buffers help maintain
constant pH.
A buffer is a weak acid
and its corresponding
base.