Electrons and Chemical Bonding

Elements are compounds what letters are to words26 letters make up all the words we know

Chemical bondingJoining of atoms to form new substances

(molecules or chemical formulasThe new compounds (Substances) have

different properties than the elements they are made up of

Chemical bondAn interaction that holds 2 atoms togetherChemical bonds form when electrons are

shared, gained, or lost

Remember…# of electrons = # or protons (atomic #)Each energy level needs to be complete in

order to be called stableValance electrons

Electrons in the outermost energy levelCan be shared or traded to become stable

Drawing Valance Electrons “Lewis Dot Diagrams” MagnesiumNeonAluminumSulfur Argon

Within a group or family elements have similar characteristics based on their # of valance electronsSee page 4 for rules

Group 1-1 Group 2-2 Group 3-12 no rule Group 18- 8 (except helium 2)

The # of electrons in outermost energy level determines whether an atom will form bondsAtom in group 18 (noble gases) usually don’t

form bonds Why?

Stable outer energy level is full

Atoms with less than 8 valance electrons: Gain lose or share

electrons to become stable

Sulfur (6 valance electrons) Can share 2 or gain 2

H, He, and Li are stable with 2 electrons in the 1st energy level Be can lose 2

electrons and become stable

Ionic BondsBonds that form when electrons are

transferred from one atom to another Metals give electrons (becomes positive ion)Nonmetals take electrons (becomes negative

ion)

Ions:

Charged particles that form when atoms gain or lose electrons

Draw NaCl

The # of electrons lost from a metal element must balance with those gained by the nonmetalThese charges cancel outThe oppositely charged ions bond and become

a 3D crystal lattice (strong attraction)

Energy is needed to pull electrons from atoms

Nonmetals have nearly full energy levelThey gain electrons to be stableOxygen needs 2 electrons

If gains 2 it becomes -2 oxide ion “ide” is ending of ions that change by gaining

electrons and have a negative charge

Covalent and Metallic BondsCovalent Bonds:

Bonds formed when atoms share electrons to become stable

Form between nonmetals They share because it takes a lot of energy to

remove an electron from outermost energy level

Compounds with covalent bonds have low melting and boiling points, brittle in solid state (can be liquid, solid, or gas)

Form molecules: 2 or more atoms joined in a definite ratio. Smallest unit of a compound that has all the

properties of that compound

Simplest molecules: Molecules made of 2 covalently bonded atoms

of the same element are called diatomic molecules

Elements found in nature of diatomic molecules are called diatomic elements

H2, O2, N2 and halogens (Cl2, F2, B2, I2)They share valance electrons to become stable

Complex molecules: Carbon atoms form the base of many complex

molecules because it can form up to 4 bonds with other elements. Plastics, carbohydrates, petroleum

Metallic Bonds: A bond formed by attraction between positively

charged metal ions and the electrons in the metal Positive metal ions form when atoms lose electrons

Metal atoms are packed so closely their outer energy levels overlap allowing valance electrons to move throughout the metal The electrons cancel the + charge of the ions

Metallic bonds give metals their properties Conductivity, malleability, ductility Bonds remain even if shape changes

Questions:1. Which of the following type of bonds deals mostly with metals?a) Ionic Bondsb) Metallic Bondsc) Covalent Bondsd) Polar Covalent Bonds

2. What is the difference between an ionic bond and a covalent bond?

3. Ionic bonds can be basically explained as:a) an attraction between two oppositely charged ionsb) an attraction between two like charged ionsc) sharing between a pair of electronsd) electrons are very tightly bound with the nucleus