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Atomic Orbitals
Chapter 2
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Electrons are always moving
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Outside the nucleus in atomic orbitals
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Average distance from nucleus (size of orbital)
is directly proportional to energy level
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Electrons in highest energy level (valence
electrons) are responsible for chemical
properties of the atom
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An Introduction Chemistry
Lecture 2: Energy Levels and
Chemical Bonding
Atomic Orbitals
Maybe… usually…
Atomic Orbitals
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Energy levels of atoms are quantized
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Electrons can move between orbitals
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Quantized: the number of possible values or
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states of a system is limited to certain
discrete values
When an atom becomes excited, electrons
jump up in energy level
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Atoms are most stable in ground state
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Ground state: the state in which all electrons
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The energies of electrons can be at certain
values only, and never in between
occupy the lowest energy orbital available
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Atomic Orbitals
Atomic Orbitals
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Third energy level
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Second energy level
Excited electrons will release energy as light in
order to return to lower energy levels
Energy
absorbed
Lowest energy level (“shell”) contains only 2
electrons
2nd and 3rd energy levels contain 8 electrons
each
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Electrons at the highest energy level are on
average the farthest from the nucleus
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These outermost electrons (valence electrons)
are the ones involved in bonding
First energy level
Atomic
nucleus
Energy
released
(as light)
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Atoms
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Draw Configuration Diagrams
Atoms are electrically neutral
H
C
Hydrogen: ? protons
? electrons
Helium: 2 protons
2 neutrons
2 electrons
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Neon:
Carbon: ? protons
? electrons
O
Oxygen: ? protons
? electrons
10 protons
10 neutrons
10 electrons
What do these elements have in common?
Ions
Ions
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Atoms are most stable when their valence shell
is full
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When an atom loses electrons, it has more
protons than electrons
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Atoms will gain, lose, or share electrons in
order to obtain a full valence shell
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This gives it what kind of charge?
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These are called cations
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Ions are charged particles that form when
atoms gain or lose electrons
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Important for electrostatic attractions,
electrical conduction
Ions
Ionization Energy
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When an atom gains electrons, it has more
electrons than protons
•
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This gives it what kind of charge?
•
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These are called anions
It takes energy to remove an electron from an
atom
Ionization energy: the minimum energy
required for an electron to overcome the
attractive force of its nucleus
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Different elements have different ionization
energies
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The lower the ionization energy, the more
likely the atom will lose an electron
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Ionization Energy
Bonding Terminology
•
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Chemical bonds: the interaction between atoms
and ions that cause them to associate with
each other
Ionic bonds: bonds resulting from the transfer
of electrons
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Covalent bonds: bonds formed by the sharing
of electrons
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What do the elements with the highest
ionization energies have in common?
• The elements with the lowest?
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Ionic Bonds
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different types of atoms or ions bonded
together
Ionic Bonds
(Page 22-11)
Electrons are transferred from one atom to
another
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Creates cations and anions
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Opposites attract
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Compounds: chemical made up of two or more
Product formed is called an ionic compound or a
salt
Ionic Bonds
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Ionic Bonds
Individual molecules do not exist
Rather, the ions arrange in a 3D crystal
structure that…
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Maximizes contact between opposite charges
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Minimizes contact between like charges
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Covalent Bonds
Covalent Bonds
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Electrons are shared between atoms
•
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Results in an energeticallyenergetically-favorable (and thus
more stable) state for both atoms
By far the most common way that atoms
interact
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Very strong – require a chemical change to be
broken
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Provide the framework for the large, complex
molecules that make up the body
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Results in a molecule
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Some molecules are made of only one type of
atom (examples: oxygen, hydrogen)
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Most molecules are compounds
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Example: Formation of Methane
Example: Formation of Water
Example: Formation of Water
Activity
Molecules have precise shapes
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Complete the table on page 22-8 in your study
packet
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Determine how many electrons the atom needs
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Remember: hydrogen can only form one
covalent bond
Atom (proton #)
Symbol
# of Bonds
Example with hydrogen
Hydrogen (1)
Water looks
familiar…
Oxygen (8)
Sulfur (16)
Carbon (6)
Nitrogen (7)
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Covalent Bonding
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Sometimes atoms have to share more than one
pair of electrons
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These multiple bonds are stronger than single
bonds and take more energy to break
Double Bond
Molecule of oxygen gas (O2)
Covalent Bonds and Symmetry
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Sometimes in covalent bonds electrons are
shared equally between atoms
Triple Bond
Molecule of nitrogen gas (N2)
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Covalent Bonds and Symmetry
These are called non
non--polar covalent bonds
Covalent Bonds and Symmetry
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This is not always the case
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The same is true of bonded atoms
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What happens when you give two siblings some
candy to share?
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One will likely be more electronegative
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Electronegativity:: a measure of the attraction
Electronegativity
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The bigger stronger one will take more candy
because he/she can!
of an atom to a shared pair of electrons
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•
Covalent Bonds and Symmetry
The more electronegative atom will pull more
of the bonding electrons to itself
This is called a polar covalent bond
Covalent Bonds and Symmetry
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This asymmetry in charge density
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One side of the molecule is slightly positive
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The other side is slightly negative
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Covalent Bonds and Symmetry
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Since opposites attract, positive poles on one
molecule will be attracted to negative poles on
another molecule
These interactions are called dipole
dipole--dipole
Covalent Bonds and Symmetry
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When a hydrogen atom is bound to a small,
highly electronegative atom (usually O, N, or F)
a highly polar bond is formed
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This results in unusually strong dipoledipole-dipole
forces called hydrogen bonds
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Not technically bonds – intermolecular forces
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Weaker than covalent or ionic bonds, but
strong enough to powerfully influence the
properties of chemicals
forces
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Best example: water
Hydrogen Bonding
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