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Physical Science Chapter 7 notes
Physical Science Chapter 7 Atoms and Bonding


7-1 What is Chemical Bonding?

Chemical Bonding is the combining of elements to form new substances.

The rules of chemical bonding are determined by the structure of the atom.

The nucleus contains protons (+) and neutrons (neutral) and has an overall positive charge.
The electron cloud has electrons with a negative charge.
Overall  - the atom is neutral: protons and electrons balance each others' electrical charges.

Electrons within the "cloud" are arranged in energy levels.  The first energy level can hold 2 electrons; the second 8; the third 18 and so on.
The electrons in the outermost energy level are called "valence" electrons.

Atoms with a filled outermost level (or 8 electrons) are very stable.

The electrons in the outermost energy level determine if the atom will form chemical bonds.

To get "stable" an atom will gain or lose electrons.


7-2  Ionic Bonds

Ionic bonding is bonding that involves a "transfer" of electrons.

(Charged atoms are called "Ions.")

An atom that gains or loses electrons will become charged - no longer neutral.
Metals tend to "lose electrons" and nonmetals tend to "gain electrons."

The process of removing electrons is called "ionization."

The energy needed to do this is called "ionization energy."

The tendency of an atom to attract electrons is called "electron affinity."

Ions in compounds are often arranged in a regular repeating crystal pattern called a
"crystal lattice."
Octet Rule:  all ions must have 8 electrons in their outter shell to be stable.

Cations: Positive ions and metals
Anions: Negative ions and nonmetals

Lewis dot structure: Dots are placed around the symbol of an element to represent the number of valence electrons.



7-3  Covalent   Bonds

Covalent bonding is bonding in which  "electrons are shared." (Not transferred!)

Dot diagrams represent the valence electrons in bonding where electrons are shared.

Diatomic elements are those which exist in nature as two atoms                                                covalently bonded together.

Molecule:   combination of atoms formed by covalent bonds.

Covalently bonded solids tend to have "low melting points" unless they are very large molecules - "network solids."


Polyatomic ion:  A group of covalently bonded atoms that act like a single                                     atom when combining.

7-4  Metallic Bonds

Metallic bonds are formed by the elements of metals.  Their outer electrons form a common electron cloud - a "sea of electrons."

Metals are:

malleable
ductile
conductors of heat and electricity
high melting points

7-5            Predicting Types of Bonds

Three different types of bonds are formed by atoms combing:
ionic bonds
covalent bonds
metallic bonds


The property most important for predicting bond type is "the number of valence electrons."

Elements to the left and center of the periodic table are metals (metallic bonds).

Metals also tend to lose electrons easily while nonmetals tend to gain electrons easily.  Compounds formed between metals and nonmetals will have "ionic bonds."


Compounds formed between elements that have similar tendencies to gain electrons will have covalent bonds.

Bonds between nonmetals on the right side of the periodic table will have covalent bonds.


The number of electrons in the outermost energy level of an atom, the valence electrons, determines how an atom will combine with other atoms.

Oxidation Number:   The number of electrons an atom gains, loses, or shares when forming chemical bonds.

Oxidation number describes an atom's combining ability.



When using oxidation numbers to predict how atoms will combine remember:

The sum of the oxidation numbers in a compound must be zero.