Chemical Bonding

Chemistry Unit 2

7th Grade Science

Mrs. Ryan

Sodium Chloride- ionic compound

Water- Polar covalent compound

Hydrogen Molecule- nonpolar covalent

Definition

• The forces that hold particles of matter together

• Can be ionic bonds or covalent bonds

Why elements would want to form a bond or

The Dating Game

• Bonds are formed because of the number of electrons in the outer energy levels of an atom

• Atoms that do not have a complete outer energy level will either– Share– Give up– Or gain electrons

to make themselves more complete or stable, like the noble gases.

2 or 8 that is the question

• Elements that want a stable outer energy level will need to meet certain requirements to be stable.

• Energy level configurations can be 2,8,18,32.• The most common is 2 or 8 electrons in the

outer level which makes the atom stable, depending on which column of the periodic table it is, you will know how many electrons an atom of the element needs to become stable.

• For instance Cl is in 17/7A so it needs one electron to make 18, or 8 in its outer level.

2 or 8 that is the question

• Elements want to be stable.

• Energy level configurations can be 2,8,18,32.

• Remember- the max # of electrons in the outer level can only be 8.

• An element that has 2 or 8 in its outer most level will be stable

The Dating Game

• Why the dating game analogy? Look-

Atoms want to be complete, more stable, at ease, just like people when they want to find that special someone that makes them feel fulfilled. They want to spend the rest of their life with them either to share, or give to or receive from, just like the atoms do with electrons.

Neutral Atoms

• Neutral atoms are those that do not have any charge to them, or those that have the same number of protons as electrons

• Neutral atoms do not have to stay neutral

Ions

• When atoms lose or gain an extra electron they become ions or charged particles.

• Ions have different #s of protons and electrons than a neutral atom.

• If they gain an electron they become a negative(-) ion.

• If they lose or give up an electron, they become a positive(+) ion.

Bonds and Energy

• When bonds form, energy can be absorbed or released– If the energy is released, it is an exothermic

reaction– If energy is absorbed, it is an endothermic

reaction

Metals vs Nonmetals

• Usually metals lose electrons and

Nonmetals gain electrons

For example-

Sodium (Na) is a metal, it loses an electron and becomes a +1 Na atom.

Chlorine, is a nonmetal, it gains an electron and becomes a -1 Cl atom.

Ionic bonds

• Are bonds formed between oppositely charged ions (back to the dating game -opposites attract.)

– For example, Na has 1 extra electron it needs to get rid of to be stable and Cl needs 1 more electron to make it stable. They bond and form NaCl

Covalent Bonds

• Are bonds where one or more electrons are shared between atoms to complete outer energy levels

• Can be polar or nonpolar covalent bonds

Polar Covalent bonds

• In polar covalent bonds, one end of the molecule that is formed has a slightly negative charge and the other end is slightly positive

Polar Covalent Bond Forming

Nonpolar covalent bonds

• There are no negative or positive ends in a Nonpolar covalent bond

• (Polar meaning poles, like north vs south so nonpolar = no poles!)

Nonpolar Covalent Bond Forming