AP Bio Chapter 2- Basic Chemistry

Topics: Atom, Chemical bond, Hydrogen Pages: 7 (1207 words) Published: September 15, 2014
9/22/2011

Basic Chemistry

Why are we studying
chemistry?
• Biology has chemistry at its foundation

Elements
• All matter composed of basic substances
called elements
• Living organisms require about twenty of
the known elements

Together, carbon, hydrogen, nitrogen
and oxygen make up 95% of the
elements found in the body.

Atoms
• All elements made of tiny particles called
atoms
• Made up of:
– Nucleus
• contains protons (+ charge) and neutrons
(no charge)

– Outside the nucleus
• Contains electrons (extremely small, - charge)

– In an atom, # of protons = # of electrons
– SO…Atoms are electrically neutral!

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What makes elements
different from one another?
• Atomic number – the number of

• Different elements contain
different numbers of PROTONS!

protons in the atoms of a particular
element
– Ex: Hydrogen has one proton and an atomic
number of 1

• Atomic weight –
# of protons + # of neutrons = atomic weight
(approx.)

Atomic symbols – the periodic table
ATOMIC NUMBER

6

C

SYMBOL OF ELEMENT

Carbon

NAME OF ELEMENT
ATOMIC WEIGHT

12.01

Isotopes
• Atoms of the SAME element with a
DIFFERENT number of neutrons
– Unstable isotopes can be radioactive causing
radiation.
– In anatomy:
• a radioactive isotope can be introduced to trace a
metabolic pathway.
• Radioactive isotopes can change chemical
structures
used to treat cancers

CARBON

Atomic bonding
• The goal of bonding is
to produce a full &
stable outer electron
shell.
– 1st shell (closest to
nucleus) – 2 electrons
to be full
– 2nd shell – 8 electrons
to be full
– 3rd shell – 8 electrons
to be full

Bonding properties
• Effect of electrons
– chemical behavior of an
atom depends on its
electron arrangement
• the number of electrons in
its outermost shell, the
valence shell

How does this
atom behave?

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Bonding properties
• Effect of electrons
– chemical behavior of an atom depends on
number of electrons in its outermost shell

How does this atom behave?

Elements & their valence shells
• Elements in the same row have
the same number of shells

How does this atom behave?

Elements & their valence shells
• Elements in the same column
have the same valence & similar
chemical properties

Elements & their valence shells
• Moving from left to right, each
element has a sequential addition
of electrons (and protons)

How do they achieve stable
structure?
• Gain or lose electrons

form ionic bonds

– Ex: Sodium has 1 electron in its outer shell to LOSE
(Na+)
• Positive ion = cation

– Chlorine has 7 electrons in its outer shell – wants to GAIN one (Cl-)
• Negative ion = anion

• Opposite charges attract
an ionic bond is
formed. (NaCl)
• Relatively weak bond (in aqueous solution)
– Note: in biology, we are pretty much only concerned
with behavior in solution, because that’s where all our
chemical reactions take place – living things are 70%
water!!!

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How do they achieve stable
structure?

• Sharing electrons –
covalent bond
• Ex: Each Hydrogen atom
has one electron in the
outer shell.
– Two hydrogen atoms can
get together and share
these electrons.
– Covalent bonds can be
single (one electron pair),
double (2 electron pairs)
or triple (3 electron pairs).
– Strong bonds

Polar covalent bonds
• Pair of electrons not shared equally by 2
atoms
• Ex: Water
– oxygen has stronger “attraction” for the
shared electrons than hydrogen
– oxygen has higher electronegativity
• What’s electronegativity?

Hydrogen bonds
• Positive H atom in
1 water molecule is
attracted to negative O in
another
• Can occur wherever an
-OH exists in a larger
molecule
• Weak bonds
• Intermolecular force

Polar covalent bonds
• 2 hydrogens in the water molecule form an
angle
• Water molecule is polar
– oxygen end is –
– hydrogen end is +

• Leads to many
interesting...
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