“W HY A TOMS C OMBINE ; C HEMICAL B ONDS ”

CHEMICAL BONDING When elements come together to form new substances, it is called chemical bonding. The electrons in the outermost energy level ( valence electrons ) of an atom will determine if a chemical bond will happen or not

W HY DO ELEMENTS COMBINE TO FORM COMPOUNDS ? – Atoms want to be stable – To be stable, the outer energy level needs 8 electrons (exceptions: H & He-only have 2)

S TABLE OR UNSTABLE ? 10 p + 11 n 0 e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

S TABLE OR UNSTABLE ? 15 p + 15 n 0 e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

S TABLE OR UNSTABLE ? 3 p + 2 n 0 e-e- e-e-

A N ATOM THAT IS NOT STABLE CAN BECOME STABLE BY : -losing or gaining (transferring) electrons -sharing electrons When atoms gain, lose, or share electrons with another atom, a chemical bond forms.

T YPES OF CHEMICAL BONDS : Ionic Covalent Metallic

I ONIC BOND : -chemical bond where electrons are transferred from one atom to another -atoms become ions when electrons are transferred -forms between a metal and a nonmetal -very strong bonds

I ONIC BOND : (Charges) Oxidization # Formula Na +1 Cl -1 NaCl

I ONIC BOND : Na +1 Cl -1

H OW CAN ATOMS CHARGE BE DETERMINED ? Li atomic #3 In group 1 → 1 valence e- Easiest to lose 1 e- Protons = +3 electrons = -2 Charge = +1 Mg atomic #12 In group 2 → 2 valence e- Easiest to lose 2 e- Protons = +12 electrons = -10 Charge = +2 O atomic #8 In group 6 → 6 valence e- Easiest to gain 2 e- Protons = +8 electrons = -10 Charge = -2 F atomic #9 In group 7 → 7 valence e- Easiest to gain 1 e- Protons = +9 electrons = -10 Charge = -1

H OW CAN ATOMS CHARGE BE DETERMINED ? Li Mg O F

I ONS COME TOGETHER TO FORM NEUTRAL COMPOUNDS Li +1 F -1 → LiF Li +1 O -2 → Li 2 O Mg +2 F -1 → MgF 2 Mg +2 O -2 → MgO

C OVALENT BOND : -chemical bond where electrons are shared between atoms -forms between 2 nonmetals - not as strong as ionic bonds - Electron Dot Diagrams represent the electron sharing

E LECTRON D OT D IAGRAMS H O Cl Al

C OVALENT MOLECULE :

D RAW ELECTRON DOT DIAGRAMS FOR THE FOLLOWING COMPOUNDS : CH 4 C Cl 2 MgF 2 H H H H

I ONIC OR COVALENT ? H2OH2O 2 nonmetals, so it is covalent CaCl 2 metal & nonmetal, so it is ionic Fe 2 O 3 metal & nonmetal, so it is ionic CO 2 2 nonmetals, so it is covalent NO 2 2 nonmetals, so it is covalent

M ETALLIC B ONDS bonding between atoms within metals. valence electrons continually move from one atom to another and are not associated with any specific pair of atoms Properties: Malleable (bendable) Good conductors electricity Good conductors of heat Shiny-luster High melting point Hard not brittle High boiling points

M ETALLIC B ONDS Ions surrounded by a “sea of electrons”

T ERMS Valence electron Electron affinity Ionization energy Electron dot diagram Oxidation number

T ERMS Valence electron: electrons contained in the outermost electron shell Electron affinity: the energy change when an electron is added to a neutral atom to form a negative ion Ionization energy: energy necessary to remove an electron from the neutral atom Electron dot diagram: element symbol surrounded by dots representing valence electrons. Oxidation number: how many electrons are lent (+) or borrowed (-)