1. Chemistry Mrs. Partridge
Chemical Bonds
Chemistry
Mrs. Partridge

2. Chemical Bonding
Chemical Bonding – the combination of atoms of elements to form new substances
A chemical bond is a force that holds atoms together.
               
                           
     
sodium metal + 
chlorine gas
table salt

3. The electrons farthest away from the nucleus (valence electrons) play the most significant role in determining how atoms combine.

4. Octet Rule – atoms with 8 (2 if H or He) are stable; elements with less react with other elements in order to fill their outer shell (valence shell)

5. There are 2 ways atoms can achieve a noble gas configuration:
They transfer electrons
They share electrons

6. Ionic Bonds
Ionic bonds are formed when atoms transfer (gain or lose) electrons
Because this bond involves the transfer of electrons, one atom gains electrons and the other atom loses electrons

7. Ionic Bonds
When an atom loses an electron, it becomes positively charged – a CATION
When an atom gains an electron, it becomes negatively charged – an ANION
ION – an atom with a charge

8. If it isn’t love, what’s going on?
Because positives and negatives attract, a bond is formed

10. The cation is always written first in the formula.
Ionic Bonds
The cation is always written first in the formula.

11. Ionic Bonds
Ionic bonds occur between a metal and a nonmetal, or involve a polyatomic ion.
Polyatomic ions – a group of atoms that together have a charge and function as a single unit

12. Ionic Bonds
Ionization Energy – the amount of energy needed to completely remove an electron from an atom or ion
1st electron held the least tight
2nd electron harder to remove
Electron Affinity – name given to the energy change that occurs when an electron is added to an atom or ion
Halogens have the highest electron affinity because they only need 1 electron

13. Oxidation Numbers can predict how atoms will combine.
Ionic Bonds
Oxidation Numbers can predict how atoms will combine.
We’ll use the criss-cross method for ionic compounds.
First check for opposite charges – opposites attract Mg Cl-1
Place the cation first
Criss-cross the number – it becomes a subscript
Mg Cl-1  MgCl2
A one is implied, do not write it as a subscript

14. Covalent Bonds
Covalent bonds are formed when atoms share electrons to fill their outer shells.

15. Covalent Bonds
The positively charged nucleus of each atom simultaneously attracts the negatively charged electrons that are being shared.
The electrons spend most of the time between the atoms. The attraction between the nucleus and the shared electrons holds the atoms together.

16. Covalent Bonds

17. Covalent Bonds
Non-metallic atoms form covalent bonds in units called MOLECULAR COMPOUNDS
Diatomic elements – covalent bonds between 2 atoms of the same element (H, Cl, O, F, Br, I, N)

18. Covalent Bonds
Double bonds consist of 2 pairs (4 e-) of electrons being shared
Triple bonds consist of 3 pairs (6 e-) of electrons being shared
The more pairs of electron shared the shorter and stronger the covalent bond

19. Covalent Bonds
Electronegativity – a periodic property; the attractive force an atom exerts on shared electrons in a chemical bond
When electrons aren’t shared equally, the bond is POLAR

20. Covalent Bonds
Polarity – the measurement of inequality in distribution of bonding electrons. Polarity is calculated using the difference between the electronegativities of the atoms. The higher the electronegativity the greater the attraction for the electron.
Electronegativity Difference
Bond Type
0 – 0.5
Covalent or slightly polar covalent
0.5 – 1.7
Polar covalent
> 1.7
Ionic

21. Metallic Bonds Metallic bonds form between atoms of metals.
The outer electrons of the atoms form a common electron cloud.
Metal crystals form when atoms crowd together and the outer-level orbitals overlap.
Electrons delocalized – electons move easily form atom to atom; they aren’t held in a specific “locality”

22. The End!