1. CHEMISTRY

2. Composition of Matter
Matter - Everything in universe is composed of matter
Matter is anything that occupies space or has mass
Mass – quantity of matter an object has
Weight – pull of gravity on an object

3. Elements
Pure substances that cannot be broken down chemically into simpler kinds of matter
More than 100 elements (92 naturally occurring)

4. 90% of the mass of an organism is composed of 4 elements (oxygen, carbon, hydrogen and nitrogen)
Each element unique chemical symbol
Consists of 1-2 letters
First letter is always capitalized

5. Atoms
The simplest particle of an element that retains all the properties of that element
Properties of atoms determine the structure and properties of the matter they compose
Our understanding of the structure of atoms based on scientific models, not observation

6. The Nucleus Central core
Consists of positive charged protons and neutral neutrons
Positively charged
Contains most of the mass of the atom

7. The Protons
All atoms of a given element have the same number of protons
Number of protons called the atomic number
Number of protons balanced by an equal number of negatively charged electrons

8. The Neutrons
The number varies slightly among atoms of the same element
Different number of neutrons produces isotopes of the same element

9. Atomic Mass Protons & neutrons are found in the nucleus of an atom
Protons and neutrons each have a mass of 1 amu (atomic mass unit)
The atomic mass of an atom is found by adding the number of protons & neutrons in an atom

10. The Electrons
Negatively charged high energy particles with little or no mass
Travel at very high speeds at various distances (energy levels) from the nucleus

11. Electrons in the same energy level are approximately the same distance from the nucleus
Outer energy levels have more energy than inner levels
Each level holds only a certain number of electrons

12. Energy Levels Atoms have 7 energy levels
The levels are K (closest to the nucleus), L, M, N, O, P, Q (furthest from the nucleus)
The K level can only hold 2 electrons
Levels L – Q can hold 8 electrons (octet rule)

13. Periodic Table
Elements are arranged by their atomic number on the Periodic Table
The horizontal rows are called Periods & tell the number of energy levels
Vertical groups are called Families & tell the outermost number of electrons

14. The Energy Levels of Electrons
Energy is the capacity to cause change
Potential energy is the energy that matter has because of its location or structure
The electrons of an atom differ in their amounts of potential energy
An electron’s state of potential energy is called its energy level, or electron shell
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

15. (a) A ball bouncing down a flight of stairs provides an analogy
Fig. 2-8
(a) A ball bouncing down a flight
of stairs provides an analogy
for energy levels of electrons
Third shell (highest energy
level)
Second shell (higher
energy level)
Energy
absorbed
Figure 2.8 Energy levels of an atom’s electrons
First shell (lowest energy
level)
Energy
lost
Atomic
nucleus
(b)

17. Compounds Most elements do not exist by themselves
Readily combine with other elements in a predictable fashion

18. A compound is a pure substance made up of atoms of two or more elements
The proportion of atoms are always fixed
Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound

19. Molecules are the simplest part of a substance that retains all of the properties of the substance and exists in a free state
Some molecules are large and complex

20. The physical and chemical properties of a compound differ from the physical and chemical properties of the individual elements that compose it

21. Chemical Formulas
Subscript after a symbol tell the number of atoms of each element
H20 has 2 atoms of hydrogen & 1 atom of oxygen
Coefficients before a formula tell the number of molecules
3O2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen

22. The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in their outermost energy level
Atoms are most stable when their outer most energy level is filled

23. Most atoms are not stable in their natural state
Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions)
In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed that store energy

24. Covalent Bonds
Formed when two atoms share one or more pairs of electrons

25. A compound is a combination of two or more different elements
Covalent bonds can form between atoms of the same element or atoms of different elements
A compound is a combination of two or more different elements
Bonding capacity is called the atom’s valence
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

26. Single covalent bond Double covalent bond
Fig. 2-UN5
Single
covalent bond
Double
covalent bond

27. Electronegativity is an atom’s attraction for the electrons in a covalent bond
The more electronegative an atom, the more strongly it pulls shared electrons toward itself
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

28. In a nonpolar covalent bond, the atoms share the electron equally
In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electron equally
Unequal sharing of electrons causes a partial positive or negative charge for each atom or molecule
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

29. Fig. 2-13
 – O H H + +
Figure 2.13 Polar covalent bonds in a water molecule
H2O

30. Figure 2.12 Covalent bonding in four molecules
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)
Figure 2.12 Covalent bonding in four molecules
(d) Methane (CH4)

31. Fig. 2-UN7

32. Ionic Bonds Some atoms become stable by losing or gaining electrons
Atoms that lose electrons are called positive ions (cations)

33. Ionic bond Electron transfer forms ions Na Sodium atom Cl
Fig. 2-UN6
Ionic bond
Electron
transfer
forms ions Na
Sodium atom Cl
Chlorine atom
Na+
Sodium ion
(a cation)
Cl–
Chloride ion
(an anion)

34. Atoms that gain electrons are called negative ions (anions)
Because positive and negative electrical charges attract each other ionic bonds form

35. Hydrogen Bonds
A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
In living cells, the electronegative partners are usually oxygen or nitrogen atoms
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

36.   + Water (H2O) + Hydrogen bond   Ammonia (NH3) + + +
Fig. 2-16
  +
Water (H2O) +
Hydrogen bond
 
Ammonia (NH3)
Figure 2.16 A hydrogen bond + + +

37. Fig. 2-UN9

38. Van der Waals Interactions
If electrons are distributed asymmetrically in molecules or atoms, they can result in “hot spots” of positive or negative charge
Van der Waals interactions are attractions between molecules that are close together as a result of these charges
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

39. Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface.
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings