Geneva High School Integrated Science
Chapter 6 – Chemical Bonds
Academic Content Standards covered in this chapter:
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Illustrate that atoms with the same number of positively charged protons and negatively
charged electrons are electrically neutral;
Describe how ions are formed when an atom or a group of atoms acquire an unbalanced
charge by gaining or losing one or more electrons;
Show how atoms may be bonded together by losing, gaining or sharing electrons.
6.1 – Ionic Bonding
Stable Electron Configurations
KEY: When the highest occupied energy level of an atom has eight valence electrons (or
two in the case of helium), the atom is stable and not likely to react.
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The chemical properties of an element depend on the number of valence electrons.
All atoms, except hydrogen and helium, need 8 valence electrons in order to be stable.
Hydrogen and helium, because they only have one energy level, only require 2 valence
electrons.
An electron dot diagram is a model of an atom in which each dot represents a valence
electron.
examples: see page 158 in textbook
Ionic Bonds
Key: Some elements achieve stable electron configurations through the transfer of
electrons between atoms. This is an ionic bond.
Transfer of Electrons
 The formation of sodium chloride is a good example of an ionic bond. (See example in
book on page 159.)
Formation of Ions
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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 on the atom is not balanced and the atom is not neutral.
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An atom that has a net positive or negative electric charge is called and ion.
The charge on an ion is represented by a plus or a minus sign.
Ions that gain electrons have a negative charge, and are called anions.
Ions that lose electrons have a positive charge, and are called cations.
Formation of Ionic Bonds
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A chemical bond is the force that holds atoms or ions together as a unit.
An ionic bond is the force that holds cations and anions together.
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A chemical formula is a notation that shows what elements a compound contains and
the ratio of the atoms or ions in the compounds.
examples: (page 161)
6.2 – Covalent Bonding
Covalent Bonds
 A covalent bond is a chemical bond in which two atoms share a pair of valence
electrons.
example: a hydrogen atom has one valence electron, but wants two. If two hydrogen
atoms share their electrons, they can achieve a stable electron configuration.
 Covalent bonds can be single bonds, double bonds, or triple bonds, and are
represented by dashed lines between the element symbols.
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A molecule is a neutral group of atoms that are joined together by one or more covalent
bonds.
Key: The attractions between the shared electrons and the protons in each nucleus hold
the atoms together in a covalent bond.
Many nonmetal elements exist as diatomic molecules.
 Diatomic molecules consist of two atoms of the same element.
 F2, N2, Cl2, Br2, I2, H2, O2
Polar Covalent Bonds
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A polar covalent bond is one in which electrons are not shared equally.
KEY: When atoms form a polar covalent bond, the atom with the greater attraction
for electrons has a partial negative charge. The other has a partial positive charge.
example: water
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Because water is polar, water molecules are attracted to each other and require energy
to pull them apart.
Remember our activity when we dropped water on the penny.
Also accounts for the cohesiveness of water.
Writing Binary Compound Formulas
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binary compound – a compound composed of only two elements.
When writing binary compound formulas, you need to follow these steps:
Write down the symbols of the elements, along with their oxidation numbers.
There will always be an element with a positive oxidation number, and an element with a
negative oxidation number.
3. Use subscripts to balance out the oxidation numbers so that the positive number equals
the negative one. (See our website for more help on this topic.)
 oxidation number – the number of electrons an atom will lose, gain, or share in
order to become stable.
See page 174 for more practice on writing binary formulas.
Naming Binary Compounds
1. Write down the name of the first element in the compound.
2. Write down the root of the second element in the compound.
3. Add –ide to the root.
Example: MgCl2
1. - Write down the name of the first element in the compound.
Magnesium
2. Write down the root of the second element in the compound.
Chlor
3. Add –ide to the root.
Magnesium Chloride
For the test, you also need to know how to count the number of atoms in a chemical
formula. Please see our worksheets for that.