What is Matter?
• Matter is any substance in the universe that
has mass and occupies space
• All matter is composed of extremely small
particles called atoms
• Every atom has the same basic structure
– Core nucleus of protons and neutrons
– Orbiting cloud of electrons
More Models of Atoms
Note electron cloud
Note
electron
cloud
Look at the samples at
the front desk
• Element
– A substance that cannot be broken
down by ordinary chemical means (one
type of atom)
• Does anyone know the chemical
symbol for these?
Iron, Oxygen and Hydrogen
• Where can we find this information?
What kind of information can we get from the periodic table?
1
H
1.0079
12
C
12.010
What do these numbers stand for?
Chemical Formulas
• The chemical formula of a substance indicates:
– The elements in the molecule
– The number of atoms of each element in the
substance
• Example:
6H2S04
– 2 atoms of the element hydrogen; 1 atom of
the element sulfur; 4 atoms of the element
oxygen
• A number in front of substance indicates how
many molecules of that substance there are:
– There are 6 molecules of H2S04 in the example
Electron shells
Atomic number = number of protons =
number of electrons for element
Electrons vary in the amount of energy they
possess, and they occur at certain
energy levels or electron shells.
Electron shells determine how an atom
behaves when it encounters other
atoms
Electrons
• Each electron shell has a specific # of orbitals
– First orbital holds up to two electrons
Fig. 3.3
Atoms with incomplete
electron orbitals are
more reactive
Stability
• Atoms will react to
maintain 8 electrons in
their valence shell
(except the first shell
which is full at 2
electrons)
• If valence shell has less
than 8 electrons the
atom will gain, lose or
share electrons to
remain STABLE.
Question:
Do you feel good
when you and your
friend share things?
How would you feel
if your friend gave
you something to
make you happy?
http://www.coolcakesbylindsay.com/2012_07_01_archive.ht
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Types of Chemical
Bonds
The Major Chemical Bonds of Biomolecules:
– Ionic Bond
– Covalent Bond
• Non-Polar
• Polar
-Hydrogen bond
Ionic Bond – Sodium
chloride
Sodium tends to
give up its single
electron in its
valence shell
Chlorine pick up
one electron to
completely fill its
valence shell
Ionic Bonds
• Formed when electrons are completely
transferred from one atom to another
• During bonding, atoms gain or lose
electrons
• Now called ions: negatively or positively
charged
• What do we know about + and -?
• Examples; NaCl, CaCl2, K2O
Covalent Bond
• Between nonmetallic elements of
similar electronegativity
• Formed by sharing electron pairs
• Examples; O2, CO2, C2H6, H2O, SiC
• 2 types:
- Nonpolar and Polar
NONPOLAR
COVALENT BONDS
when electrons are
shared equally
H2 or Cl2
Polar Covalent Bonds: Unevenly
matched, but willing to share.
POLAR COVALENT BONDS
when electrons are shared
but shared unequally
H2O
- water is a polar molecule because oxygen is more
electronegative than hydrogen, and therefore electrons
are pulled closer to oxygen.
Electronegativity
Is a chemical property that is a
measure of the tendency of an atom to
attract a bonding pair of electrons.
(Wikipedia and www.chemguide.co.uk)
• Decreases down a group
• Increases with increasing atomic
number going across a period
• Which is more electronegative?
S or Fl, C or O, Mg or P
Put your knowledge to
work
Why is H2S a gas and H2O a liquid at
room temperature?
Write a response based on the
chemistry information you have.
Hydrogen Bonds
• Attraction between
partially (-) and partially
(+) charged atoms
• Examples:
• Exist between
adjacent water
molecules
• Between polarized
regions of same large
molecules (protein)
• Between 2 strands of
a DNA molecule
Take out a piece
of paper
1. What are the types of bonding?
2. What makes each bond different from
the others?
3. Give an example of each bond.
4. Hand in at the end of the period