Transcript Chapter 4 The Chemical Basis of Life Matter Matter = any material substance with Mass & Volume.

Chapter 4
The Chemical Basis of Life
Matter
Matter = any material
substance with Mass
& Volume
Matter
comes in 3 phases
Solid
Gas
Liquid
Solid
Definite Shape
Definite Volume
Liquid
Indefinite Shape –
takes the shape of the
container
Definite Volume
Gas
Indefinite Shape –
takes the shape of
the container
Indefinite Volume –
can expand and be
compressed
Elements
Pure substance that can not be broken
down into other substances by chemical
means
Examples of Elements
C = Carbon
Na = Sodium
O = Oxygen
Ca = Calcium
H = Hydrogen
K = Potassium
N = Nitrogen
I = Iodine
Cl = Chlorine
S = Sulfur
P = Phosphorus
• 4 elements make up 96% of all living matter
– Hydrogen (H)
– Oxygen (O)
– Nitrogen (N)
– Carbon (C)
• Most of remaining 4%
is made of:
–
–
–
–
Calcium (Ca),
phosphorus (P),
potassium (K),
sulfur (S)
• Trace elements Make
up less than 0.01 % of
body mass
– Essential to life
Atom the smallest particle making up elements
Sub-atomic Particles
Protons p+ - positive
charge, in nucleus
Neutrons n0 – no
charge, in nucleus
Electrons - e- negative
charge, orbiting nucleus
Carbon Atom
6
C
12.011
Atomic # = # of p+ and # of eCarbon has 6 p+ and 6 e-
Atomic Mass minus Atomic # = # of n0
Carbon has 6 n0
Drawing an Atom of Carbon
eee-
6 p+
6 n0
ee-
e-
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
Compounds
• Substance containing two or more elements
combined in a fixed ratio
• Properties are usually much different than
those of the elements they contain
– Ex: H2O – liquid at room temperature, while
hydrogen and oxygen are both gases
– Ex: NaCl – white crystal (table salt), while
sodium is a silver-gray metal and chlorine is
a yellowish-green gas
Isotopes
 Atoms with the same number of protons, but
different numbers of neutrons.
 Atoms of the same element (same atomic number)
with different mass numbers
 Most isotopes are stable—their nuclei do not
change over time
Radioactive Isotope
• Other isotopes contain
nuclei that will change or
decay over time
• Unstable isotopes
• Nucleus changes giving off
radiation
• May be harmful
• Can be useful in research
and/or medical diagnosis
and treatment
Let’s practice What We Just Learned
Bohr Diagram and Lewis
Structure
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells
around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
Bigger energy level = higher energy
ATOMIC STRUCTURE: Bohr Diagram
With the Bohr Diagram (Dot & Cross diagrams) elements
and compounds are represented by Dots or Crosses to show
electrons, and circles to show the shells. For example;
X
Nitrogen
X
X 7P+
7n0
XX
X
X
N
7
14
Bohr Diagrams
Draw the Bohr Diagram for the following elements:
a)
O
8
b)
16
Cl
X
17
35
X
X X
XX
X
X
8p+
8n0
X
X X
X
X
X
X
17p+
X 18n0 X
X X
X X
X
X
X
X
Bohr Diagrams
Draw the Bohr Diagram for the following elements:
c)
B
5
11
d)
10
Ne 20
X X
X X
X
X
5p+
6n0
X
X
X
10p+
X 10n0 X
X X
X
X
Valence Electrons
• The electrons on the outermost
energy level
• These electrons determine the
element’s chemical properties
and its ability to form chemical
bonds.
Lewis Structure of Atom
• The chemical symbol for the atom is surrounded
by a number of dots corresponding to the number
of valence electrons.
• Examples
– Hydrogen atom has 1 valence electron
– Fluorine atom has 7 valence electrons
H
F
Lewis Structure
• Draw the Lewis Structure for the following elements:
a)
Li
b)
c)
P
d)
Cl
Mg
Let’s practice What We Just
Learned
Chemical Bonding
Ionic and Covalent
Chemical Bonds
• Atoms react with one another to fill their
outer energy levels
• Transferring or sharing electrons creates
an attraction (chemical bond) that holds
atoms together
Noble Gases
• Helium, neon and argon are atoms which do not react
with other atoms.
• We call them “Noble Gases” because of this.
• Each of these gases has a full outer electron shell.
2p2n
He
2
4
10p10n
Ne 10
20
2,8
18p22n
18
Ar 40
2,8,8
IONIC BONDS
• Ionic bond: one atom transfers an
electron to another atom
• Oppositely charged ions are attracted
to one another forming a chemical bond
 an ionic bond
Sodium
11
Na 23
e.c. 2,8,1
11p
12n
11 protons
12 neutrons
11 electrons
Chlorine
17
Cl 35
e.c. 2,8,7
17p
18n
17 protons
18 Neutrons
17 electrons
The Sodium atom has 1
Electron in it’s outer shell.
Na
e.c. 2,8,1
Atom
The Sodium loses 1 electron
to leave a complete outer
shell.
It is now a Sodium ion with a
charge of 1 +
(Na +)
e.c. (2,8)+
Ion
+
The Chlorine atom has 7
electrons in it’s outer shell.
Cl
e.c. 2,8,7
Atom
The Chlorine gains 1 electron
to gain a complete outer
shell.
It is now a Chlorine ion with a
charge of 1 -
(Cl - )
e.c. (2,8,8)Ion
The Ionic Bond
Chlorine
atom
Sodium atom
Na
Cl
Sodium ion
+
(Na +)
-
Chlorine ion
(Cl -)
• The sodium atom loses one electron to attain a complete outer shell and become
a positive ion (Na +).
• The Chlorine atom gains one electron to attain a complete outer shell and
become a negative ion (Cl –).
• Strong forces attract the sodium and chlorine ions.
Covalent Bond
• Formed when atoms share electrons
• Electrons may be shared equally or
unequally
• Molecule: two or more atoms held
together by covalent bonds
Chlorine atom 2,8,7
2 Chlorine atoms
Outer shells only
Chlorine molecule Cl2
Electrons shared
Each outer shell has 8 electrons
Forces (bonds) between atoms in the molecule are very strong
Molecules have no overall electric charge
Covalent bonds can be represented in 3 ways:
Chlorine Cl2
Cl
Cl
Cl
Cl
Cl
Cl
16
Oxygen O 8
Oxygen atom 2,6
2 Oxygen atoms (outer shells only)
Double covalent bond
O
O
Let’s practice What We Just
Learned
LIFE DEPENDS ON THE
UNIQUE PROPERTIES OF
WATER
Water Molecule
• Water is a polar molecule
• Electrons are not shared
equally between
hydrogen and oxygen
• Electrons attracted to
oxygen more strongly
than to hydrogen
Note: Hydrogen atoms in the water
molecule are slightly positive and
the oxygen atom slightly negative
WATER’S LIFE-SUPPORTING
PROPERTIES
• Polarity of water and effects of hydrogen
bonding give water its unique properties:
– Cohesion and adhesion
– Temperature moderation
– Low density of ice compared to water
– Ability to dissolve substances
COHESION & ADHESION
• Cohesion: an attraction between like molecules
• Adhesion: an attraction between unlike
molecules
– Keep large molecules organized so they
function properly in cells
– Help transport water through roots and leaves
in plants
TEMPERATURE MODERATION
• Hydrogen bonds in water molecules
allow water temperatures to change
more slowly
– Through evaporation (sweating), water
moderates temperature  absorbs heat
energy from skin cooling the body
LOW DENSITY OF ICE
• Density: amount of matter/given volume
• For most substances, solids are more dense than
liquid state of matter
• Due to hydrogen bonding, water is the opposite
• Liquid water is more dense than solid water
• Since less dense substances float in more dense
substances, ice floats
WATER DISSOLVES OTHER
SUBSTANCES
• Solution: uniform mixture of two or more substances
• Solvent: the substance that dissolves the other
substance; present in the greater amount
• Solute: the substance that is dissolved; present in
the lesser amount
• Aqueous solution: solution where water is the
solvent
ACIDS, BASES, & pH
• Acid:
– produce H+ ions in water
– pH less than 7
– sour taste
• Base:
– removes H+ ions in water
– pH greater than 7
– bitter taste
• pH scale: range of numbers that describes how
acidic or how basic a solution is
– pH of 7 is neutral
• Buffers: substances that cause a solution to resist
changes in pH