1. Biology relies on chemistry as living things are made up of matter composed of atoms and molecules. 2. Chemical reactions within and between these molecules drive biological processes in organisms. 3. Understanding the chemical structure and reactions of matter is therefore essential for biologists to study life processes at the cellular and molecular levels.

2.  Biology has chemistry at its foundation!

3. Everything that has mass and
takes up space is
made of matter.

4.  …because all living
things are made up of
matter.
 Also, chemical changes
in matter are essential to
all life processes.
 By learning how changes
in matter occur,
biologists can gain an
understanding of the life
processes of the
organisms they study.
 Chemical structure and
reactions are central to
biological processes.
 What biological
processes can you think
of that involve
chemistry?

5. Liquid
Solid
Gas

7.  The properties of different kinds of atoms
determine the structure and properties of the
matter they compose
 (THEME: Structure and Function)

8. 1. size: 100 million = 1 cm
2. composed of
subatomic particles

10.  Central region of atom
 Makes up the bulk of the mass of the atom
 Consists of protons and neutrons

11.  Have a POSITIVE charge!
 p+
 In nucleus

12.  Neutrons (n0) are NEUTRAL!
 (carry no charge)
 In nucleus

13.  Electrons (e-) have a
negative charge!
 1/2000 the mass of p+
 High-energy particles
 Move around outside
nucleus in clouds called
orbitals.
 Orbitals correspond to
specific energy levels,
that can only hold a
certain number of e-

14.  Definition of atom
= smallest unit of a
chemical element
that retains the
properties of that
element
 Element = all same
kind of atom

15. HELIUM ATOM
N
+
+
N
-
-
proton
Energy
level
electron neutron

16. Bohr’s Model
of the Atom
electrons in orbits
nucleus

17.  All atoms of an element have
same chemical properties
 all behave the same
 properties don’t change

19.  About 25 elements are essential for life
 Four make up ~95%+ of living matter:
• carbon (C) • hydrogen (H)
• oxygen (O) • nitrogen (N)
 A few elements make up most of remaining 4%
including:
• phosphorus (P) calcium (Ca)
• sulfur (S) potassium (K)
▪ sodium (Na) chlorine (Cl)
▪ magnesium (Mg) iodine (I)
▪ iron (Fe) zinc (Zn)
▪ fluorine (F) silicon (Si)

22.  Check out Aluminum from the Periodic Table:

23.  The number of protons in an atom
determines the element
 # of protons = atomic #
 The number of protons NEVER CHANGES for
each unique element!
 this also tells you # of electrons
because:
number of e- = number of p+
(for a neutral atom)

24.  Atomic number: this number indicates the
number of protons in an atom
 Ex: Hydrogen’s atomic number is 1
▪ So hydrogen has 1 p+
 Ex: Carbon’s atomic number is 6
▪ So carbon has 6 p+
**Therefore, the number of protons
identifies the atom.

25.  The mass number is the total of protons and
neutrons in the nucleus
 Neutrons and Protons have almost exactly the
same mass
 Each one has the mass of ~1.7 x 10-24 grams

26. ATOMIC STRUCTURE
Atomic number
the number of protons in an atom
the number of protons and
neutrons in an atom (p+ + no)
Al 27
13
Mass number

27.  The average value of atomic weight of an
element
 Calculated from the atomic masses of the
isotopes of a given element, along with the
abundance of each isotope in nature.
 Based on the mass of carbon-12.

28.  Different number of neutrons
 (lighter or heavier)
 Some are unstable
 nuclear reactions / decay
 radioactivity
 Biological tool
 Biological hazard

29. Example:
http://education.jlab.org/glossary/isotope.html

30. ATOMIC STRUCTURE
Electrons are arranged in Energy Levels around the
nucleus of an atom. (Energy levels are also called energy shells)
• first energy level a maximum of 2 electrons
• second energy level a maximum of 8 electrons
• third energy level a maximum of 18 electrons

31.  Bohr Model of the atom:
All of the
protons and
the neutrons
The 1st ring can
hold up to 2 e-
The 2nd ring can
hold up to 8 e-
The 3rd ring
can hold up
to 18 e-
The 4th ring
and any after
can hold up to
32 e-

32. DOT DIAGRAMS
With Dot diagrams elements and compounds are
represented by Dots to show electrons, and circles to
show the energy levels. For example:
Nitrogen N 14
N7

33.  Electrons in the outermost energy level.
 Responsible for the chemical properties and
behavior of atoms
 Participate in
chemical bonds
 Ex: N has
N
5 valence e-

35.  Formed by the gain or loss of electrons by an
atom, creating charged atoms.
 This happens to make the atom stable.

36. SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Mass Number of an atom = number of
Protons + Neutrons in the nucleus.
3. In neutral atoms, the number of Protons = Number
of Electrons.
4. Isotopes are atoms with varying number of neutrons.
5. Electrons orbit the nucleus in energy levels, also
known as shells.
6. Each energy level can only hold a set number of
electrons.
7. Valence electrons are found in an atoms outermost
energy level.
8. Ions are charged atoms, with varying number of
electrons.