Physical Science Chapter 6
Chemical Bonds
Bonding
• Chapter 6 is about different types
of atomic bonding
• Forces of attraction is the key to
this bonding
• The physical properties of
elements is key to the different
types of bonds
Bonding
• Draw the electron
configuration of the
elements neon
and sodium
• What do you notice about
the Valence electrons and
the energy level of each
element?
Stable Electron Configurations
• When the highest occupied
energy level of an atom is filled
with electrons, the atom is
stable and not likely to react
Ionic Bonds
• Elements without complete
sets of valence electrons tend
to react
• They react to try to achieve
the stability of a full energy
level…like the noble gases
Transfer of Electrons
• Look at the electron dot diagrams for
sodium and chlorine
• What do you think these elements will want
to do?
Atomic Chemical Reaction
When sodium and chlorine react:
An electron is transferred from each
sodium atom to a chlorine atom.
Now each atom is more stable
When an atom gains or loses
an electron, the protons and
electrons are no longer
equal and the atom is not
neutral.
An atom with a positive or
negative charge is an ion
• Notice the positive and
negative charge on the new
sodium and chlorine atoms
Charge
• An ion with a negative charge is an anion.
• Chlorine in NaCl is an anion…Cl• It is negative because it has one more
electron than protons, thus a charge of 1• Anions are written using a part of the
elemental name and the suffix ide.
–chloride
• Our new sodium ion, because it
lost an electron now has more
protons than electrons, making it
positive or 1+
+
–Na
• Cations are named just using the
elemental name, sodium
Chemical Bonds
• A chemical bond is what holds atoms
or ions together
• Ionic bonds are what holds cations
and anions together
–Ionic bond forms when electrons
are transferred from one atom to
another
Chemical Bonds
• http://www.youtube.com/watch?v=QXT4OVM
4vXI
Ionization Energy
• The amount of energy used to
remove an electron from an atom
is ionization energy
• It varies form element to element
• The lower the ionization energy,
the easier it is to remove an
electron
• Which element would it be
easier to take an electron
from, Magnesium or Calcium?
Ionic Compounds
• Compounds that contain ionic bonds
are ionic compounds
• These can be represented by a
chemical formula:
–Notation that shows what
elements a compound contains
and the ratio of the atoms or ions
of these elements in the
compound: NaCl
Practice
• We want to make a compound
with magnesium and chloride
• What group is magnesium in?
• What group is chlorine in?
How will we combine these
elements?
+
=
How will we combine these
elements?
+
=
MgCl2
• MgCl2 = The subscript 2
shows how many atoms of
that element are present
• If there is not a subscript,
that implies that there is
only one atom
Ratios are Easier
• It is easier to see the number of atoms when
you break a formula down into ratios
• For example, H2O has a hydrogen to oxygen
ratio of 2:1
• Find the ratios of the following formulas:
• Sodium Chloride, NaCl=
• Magnesium Chloride, MgCl2=
• Sodium Oxide, Na2O=
Crystal Lattices
• How are the ions in a grain of salt
arranged?(162)
• Attractions between opposing
charges keeps the ions in a fixed,
repeating position
• Solids whose particles are arranged
in lattice structure are called crystals
• The shape of an ionic crystal
depends on the arrangement of
ions in its lattice
• The arrangement of the ions
depends on the ratio of ions (like
the exercise you just did) and
their relative sizes
Compare
•
•
•
•
•
Compare figure 5a and 5b (pg 162)
Answer the following questions:
1. How are the sodium ions represented?
2. How are the Chloride ions represented?
3. What do you notice about the locations of
the positive and negative ions?
• 4. What is the similarity between the diagram
of NaCl and the photograph of NaCl?
Properties of Ionic Compounds
• The properties of NaCl are typical of
other ionic compounds:
• High melting point (801 degrees Celsius)
• As a solid they are poor electric
conductors
• As a liquid they are good electric
conductors
• They shatter when struck with a hammer
• All of these properties of
ionic compounds are
explained by the strong
attractions within a crystal
lattice
• For electric current to flow, charged particles
must be able to flow from one location to
another
• Ions in a crystal lattice have a fixed position
• When they melt, the lattice breaks apart and
ions are free to flow
• Melted sodium chloride is an excellent elctric
conductor
• Complete the section 1
assessment in your book and
the questions in your
workbook for this section
Covalent bonds
• http://www.youtube.com/watch?v=yjge1WdC
FPs
Covalent Bonds
• Someone read Covalent Bonds, pg 165
• Covalent Bond: a chemical
bond in which two atoms
share a pair of valence
electrons
• Example: Hydrogen has one valence electron
• If it had one more it could reach the stability
of a full orbital for its energy level
• So it wants to share an electron with another
atom that also only has one valence electron…
• Hydrogen
• These two hydrogen atoms
that share a valence electron
form a molecule
• Molecule: a neutral group of
atoms that are joined together
by one or more covalent bonds
• The molecule is neutral because
it has two protons and two
electrons
• The attraction between the
shared electrons and the protons
in the individual nuclei holds the
atoms together in a covalent
• The chemical formula for this
covalent bond/molecule is H2
• The subscript 2 is for the 2
hydrogen atoms in the
molecule
• Diatomic molecules: Two atoms
• Many nonmetals make diatomic
molecules…why?
• Halogens, for example, all have 7
valence electrons
• If two of them share an electron
they both achieve a stable
electron configuration
Multiple covalent bonds
• Atoms can share more than one
electron
• They can share pairs
• If they share 2 pairs, it is called a
double bond
• If they share 3 pairs it is called a
triple pair
Ionic and Covalent bonds
• http://www.youtube.com/watch?v=QqjcCvzW
www
Polar Covalent Bonds
• A covalent bond in which electrons
are not shared equally is a polar
covalent bond
• Some atoms may have a greater
attraction than others and thus the
electrons spend more time near
that atom in the bond than the
other
• Because they are sharing electrons, neither
atom becomes + or – like ionic bonds.
• However, they can become partially + or –
when the electrons are shared unequally
• If so, they are assigned the symbol delta – or
delta +, depending on which one gains or
loses the electrons most
Polar and Nonpolar Molecules