Chapter 6 Notes – Chemical Bonds
Section 6.1 – Ionic Bonding
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.
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The noble gases have stable electron configurations with eight valence electrons
(or two in the case of helium) in their outer most energy level.
An electron dot diagram is a model of an atom in which each dot represents a valence
electron.
Ionic Bonds
Elements that do not have complete sets of valence electrons tend to react. Some
elements achieve stable electron configuration through the transfer of electrons between
atoms.
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When an atom gains or loses an electron, the number of protons is no longer equal
to the number of electrons. The charge of the atom is not balanced and the atom is
not neutral. An atom that has a charge is called an ion.
The charge of an ion is represented by a plus or a minus sign.
An ion with a negative charge is an anion.
An ion with a positive charge is a cation.
Metals form positive ions.
Nonmetals form negative ions.
A particle with a negative charge will attract a particle with a positive charge because
opposites attract. When an anion and a cation are close together, a chemical bond forms.
A chemical bond is the force that holds atoms or ions together. An ionic bond is the
force that holds cations and anions together.
Ionization Energy
An electron can move to a higher energy level when an atom absorbs energy. The energy
allows electrons to overcome the attraction of the protons in the nucleus.
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The amount of energy used to remove an electron is called ionization energy.
The lower the ionization energy, the easier it is to remove an electron from an
atom.
Ionization tends to increase as you move from left to right across the periodic
table and it tends to decrease as you move from top to bottom.
Ionic Compounds
A chemical formula is a notation that shows what elements a compound contains and the
ratio of the atoms or ions of these elements in the compound.
There are 3 steps that you must follow when writing a chemical formula.
1.
2.
3.
4.
First give a charge to each element.
Criss-cross the numbers but LEAVE the charges.
Place the numbers as subscripts.
Reduce the numbers if necessary.
Na and S
Na +1 S -2
Na2S
Crystal Lattices
A chemical formula does not give you the shape of a compound. Sodium chloride is
arranged in an orderly, three-dimensional structure which explains why the shape of salt
when you look at it under a microscope looks like cubes.
Solids whose particles are arranged in a lattice structure are called crystals.
Ions pack together in an orderly pattern called a network. This is what makes the
compounds so strong.
When melted or dissolved, ions conduct electricity.
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Electric current is a stream of moving electric particles.
As a solid, all the ions are locked in place.
The ions need to move to conduct electricity.
When dissolved in liquid, ionic compounds split into individual ions.
Ions in water are called electrolytes.