Transcript Atoms

Outline 2-1
Nature of Matter
I.
Matter is made of Atoms
A. Atoms are the smallest units of
matter that cannot be broken
down by chemical means.
1. Named by the Greek philosopher
Democritus
B. Atoms consist of three kinds of
particles:
1. protons
2. neutrons
3. electrons
• The subatomic
particles in a
helium atom.
C. Arrangement of parts of atom:
1. Nucleus contains:
a. protons = (+) charge; mass = 1
b. neutrons = no charge; mass =1
2. Electron cloud
a. Region where electrons are
found constantly moving
b. Electrons have (-) charge;
almost no mass (1/1840 mass of
proton)
3. No overall charge on atoms since atoms
have equal numbers of protons & electrons
D. Elements
1. An element is a substance made
of only one kind of atom (pure
substance)
2. Each element is represented by a
symbol
3. Elements differ in # of protons
4. More than 100 elements are known
but only about 2 dozen are found in
living organisms
E. Electron Arrangement
1. Electrons are grouped into different
levels
a. Inner levels have less energy
than outer levels
 Innermost level holds 2
electrons
 Other levels can hold up to 8
electrons
F. Isotopes
1. Atoms of the same element that
differ in the number of neutrons
they contain
a. Example:
Carbon-12 has 6 P and 6 N
Carbon-13 has 6 P and 7 N
Carbon-14 has 6 P and 8 N
2. All isotopes of an element have
the same chemical properties
G. Radioactive Isotopes
1. Some atoms have unstable nuclei
that break down at a constant rate
over time.
2. Uses of radioactive isotopes:
a. Used to determine ages of rocks
and fossils
b. Treat cancer
c. Kill bacteria in food
d. Used as “tracers” to follow
movements of molecules
II. Periodic Table - one box
15
Phosphorus
Symbol
P
30.97376
Round to whole #
Atomic
number =
# protons
Mass # =
# protons
+ number
neutrons
III. Atom Drawings
A. Hydrogen
B. Helium
C. Oxygen
D. Carbon
E. Nitrogen
F. Sodium
G. Phosphorus
H. Chlorine
Copy from
overhead
Do on own.
Use Periodic
Table to get
information
I. Boron
J. Fluorine
K. Silicon
L. Argon
Do for HW
IV. Atoms can bond together
A. A compound is a substance
made by chemical combination of
two or more different elements in
definite proportions
1. Examples:
a. Na joined with Cl forms
NaCl (table salt)
b. 2 H joined to O forms water
(H2O)
NaCl and H2O are chemical formulas
2. Properties of compounds
a. Physical and chemical properties of a
compound are usually very
different from the elements from
which it is formed.
b. Examples:
2 gases (H & O) combine to form
liquid water
Na is an explosive metal while Cl is a
poisonous gas. These combine to form
NaCl which is a white solid that is not
poisonous or explosive
B. Chemical Bonds
1. The force that joins atoms
together is called a chemical
bond
2. Bond formation involves the
electrons that surround each
nucleus.
3. The electrons that are available to
form bonds are called valence
electrons.
4. Reasons for bonding
a. An atom becomes stable when its
outer electron level is full.
b. If the outer electron level is not
full, an atom will react readily with
other atoms that can provide
electrons to fill its outer level
C. Ionic Bonds
1. Formed when electrons are
transferred from one atom to
another
2. An atom that has gained or lost an
electron is called an ion
a. This is because they now
contain an unequal # of
protons & electrons
b. Atom loses an electron = (+)
c. Atom gaining electron = (-)
3. Ions of opposite charges may
exchange electrons to form an
ionic bond
a. Sodium (Na) gives up its only
outer electron to become Na+.
b. Chlorine (Cl) has 7 outer
electrons and will take the electron
from Na and become Clc. The (-) Cl is attracted to (+) Na
and they form an ionic bond
Sodium atom (Na)
Chloride ion (Cl-)
Sodium ion (Na+)
Chlorine atom (Cl)
Protons
Electrons
+11
- 11
10
Protons
Electrons
+17
18
- 17
Charge
+10
Charge
-10
D. Covalent Bonds
1. Covalent bonds form when two or
more atoms share electrons to
form a molecule.
2. Sharing means the electrons
actually travel in the orbitals of both
atoms.
a. Single bond shares a pair of
electrons
b. Double bond shares 2 pairs
c. Triple bond shares 3 pairs
3. Examples = water, carbon dioxide
• Each hydrogen
atom forms a
single covalent
bond with the
oxygen atom.
• Each oval
shows the
electrons that
are being
shared
E. Van der Waals Forces
1. The slight attraction found between
the oppositely charged regions of
nearby molecules.
2. Not as strong as ionic or covalent
bonds but they can hold molecules
together, especially large ones.
3. Example:
Hold gecko feet to walls
Gecko climbing on
glass wall
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