Electrons are the key to chemical bonding specifically

Electrons are the key to chemical bonding – specifically outer shell electrons. n Only outer shell electrons are involved in bonding.

Valence Electrons – The outer shell is called the valence shell. – Electrons in the outer shell are called valence electrons Valence shell

All atoms want to be “happy” l – a happy atom has a full valence shell. l It has all of the electrons it can hold!

• The first period of elements - hydrogen and helium - can hold up to 2 electrons helium in the outer shell. – So to be happy, hydrogen wants to gain an electron. I want another electron to fill my shell… Hooray! My shell is full!

For the other periods… n …the atoms want to have 8 electrons in their 8 outer shell. 1 7 2 6 3 neon 4 5

o Chlorine wants to gain one electron

Potassium wants to lose one! (its easier to lose one electron than to gain seven!)

How many does Carbon want? • Carbon can either gain or lose 4 electrons! Why is this atom sad? Carbon It’s outer shell is not full!

How do atoms bond? • Atoms bond by gaining, losing, or sharing electrons! • …. But if you gain an electron, there will be more electrons than protons!

• That’s right! The atom is no longer neutral – it now has a charge! -An atom that has a charge is called an ion. Because I have an extra electron, I have a -1 charge!

• Ion – Atom with a charge formed when one or more valence electrons is gained or lost • Ionic bond – force of attraction between oppositely charged atoms • When an atom gains or loses electrons, it gains a charge – it becomes positive or negative. • Positive ions are attracted to negative ions + -

The Chlorine atom from before… …gained one electron to become happy. This electron gave the chlorine a negative charge Cl-

- The potassium atom would want to lose an electron. – becoming positive! K+

• So if a potassium and a chlorine meet, the chlorine will take the electron from the potassium, making both atoms into ions! Potassium Chlorine Cl- K+

• The Positive potassium is attracted to the negative chlorine – and an ionic bond is formed K+ Cl- Reaction with Sodium and Chloride KCl

Ionic compounds • Ionic compounds are usually hard, brittle, and dissolve in water. • When metals bond with nonmetals, it forms ionic compounds • Sodium chloride (table salt) and hydrochloric acid are ionic compounds

Sodium chloride (table salt) and hydrochloric acid (stomach acid) are ionic compounds Na+ Cl- Na. Cl H+ Cl+ HCl

• Covalent bond – when atoms are held together by sharing electrons • Many atoms hang onto their electrons much too tightly for them to be removed – This means they cannot form ions! • These atoms still want to fill their outer shell, but they can’t gain or lose electrons – So what can they do? • Covalent bonding simulator

They Share! • Oxygen cannot pull the electrons off of hydrogen, but it still wants a full shell.

• With a little energy, hydrogen atoms will share their electrons with the oxygen atom to make it happy, and the oxygen will share one electron with each hydrogen atom! simulation of covalent bonding in H 20

The electrons are shared • The hydrogen atoms now have 2 electrons each and the oxygen atoms have 8. The formation of water

n Water is a covalent compound. n Covalent compounds are much more common than ionic compounds. Everything from sugar to gasoline to ammonia is a covalent compound!

Metallic bonding • In metallic bonding, atoms are surrounded by a “sea” of free-flowing electrons. • They are held together by the forces within that “sea”