Download Atomic Number

Chemistry of Life
Chapter 2 (2.1 and 2.2)
Atomic Structure
• Diagram of an Atom:
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2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
In a neutral atom the number of electrons = number of protons
SUMMARY
1.
The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3. The number of Protons = Number of Electrons.
4.
5.
Electrons orbit the nucleus in shells.
Each shell can only carry a set number of
electrons.
Elements
• An element is a substance that consists of
only one type of atom.
• Examples:
Isotopes:
Isotope- An atom of an element that has a different
number of neutrons than the other atoms of that element.
Compounds
• composed of 2 or more
elements in a fixed ratio
• properties differ from
those of individual
elements
• Examples:
Ionic Bonding
• Ionic bonds form when atoms give and
take valence electrons.
• Diagram:
Covalent Bonding
• Covalent bonds form when atoms share
electrons to form a full number of valence
electrons.
• Diagram:
Molecules
• Molecules are formed when atoms are
joined by covalent bonds.
– Smallest unit of most compounds
Polar and Non-Polar Covalent Bonds
• Non-polar covalent bonds
– When the electrons are not shared equally
– One of the atoms has a greater attraction for
the electrons
• Diagram:
Van der Waals Forces
• When atoms or
molecules have attractive
or repelling forces that
are not due to ionic or
covalent bonds.
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Properties of Water
• Water is a polar molecule.
• There is a uneven distribution
of electrons
Properties of Water
• Water forms hydrogen bonds.
• Hydrogen bonds form when the
positive H atom is attracted to a
negative atom on another
molecule.
Properties of Water
• Water is cohesive.
– The molecules stick to
each other
• How does this explain
surface tension?
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Properties of Water
• Water is adhesive.
– attraction between different
molecules
• Water’s cohesive property and
adhesive property allow for capillary
action. Why is it important?
Properties of Water
• Draw a diagram of a meniscus. Label
where cohesion and adhesion occur.
Properties of Water
• Water is a great solvent.
• How does the salt and
water become a solution?
• Why is this property
important?
Properties of Water
• Water retains its
temperature.
• Why is this important?
Properties of Water
• When water freezes- it
floats.
– The density of water is
lower in its solid form
• Why is this important?
Acids and Bases
• Water can break apart into H+ and OH• Water is neutral because the number of
H+ and OH- ions are equal.
Acids and Bases
• If a substance has more H+ ions than OHions it is said to be acidic.
• If a substance has more OH- ions than H+
ions it is said to be basic.
pH Scale
• Acidic solutions
– Higher
concentration of H+
than pure water
– pH is below pH7
• Basic solutions
– Lower concentration
of H+ than pure
water
– pH is above 7
pH Scale
• pH of common items
• Each step on the pH scale
represents a factor of 10.
• Example:
Buffers
• Buffers – weak acids or bases that react
with strong acids or bases to prevent
sudden or drastic pH changes.
• Why is this important to living organisms?