Calcium chloride, CaCl, is a pure substance used on roads to control dust and to melt ice and snow.  What type of matter is this material? A Element B Atom C Compound D Gas Review elements and cmpds. How do two elements come together to make a compound?

Elements join together to become compounds because of their valence electrons

Chemical Bond Valence Electrons – the electrons in the outermost energy level of an atom This Lithium atom has one valence electron

How many valence electrons are there? Review how many electrons fit in each energy level. Carbon 4 valence electrons Beryllium 2 valence electrons Oxygen 6 valence electrons

Important!! To be stable, an atom wants a full valence energy level. Stable = “happy” or “complete” Am I stable? A stable atom is not reactive.

This atom is stable because… Look through your Bohr models and find those atoms that are already stable. This atom is stable because… Helium is stable because it has 2 electrons in the first energy level. Argon is stable because it has 8 electrons in the outer energy level. Neon is stable because it has 8 electrons in the outer energy level.

Where on the periodic table are the stable atoms found? Can introduce that these are “Noble gases” Everything in group 8A already has a full outer energy level and so is not reactive. Where on the periodic table are the stable atoms found? Noble Gases

Can introduce that these are “Noble gases” Everything in group 8A already has a full outer energy level and so is not reactive. All other atoms “want” to be stable – they want their valence to look like the Noble Gases.

How close are the other atoms to looking like a noble gas? Try it! Sort your cards by the number of valence electrons the atom has 1 2 3 4 5 6 7

Think, pair, share Do you see a pattern between where an element is found on the periodic table and its number of valence electrons?

Number of valence electrons = the number before the A So, we can just look at the periodic table to find the number of valence electrons for anything in a group A. Ask the students what the exception is (Helium has 2 valence electrons even though it is in group 8. Remember – it is in group 8 because of its stability.) Do some practice at this point to make sure students understand. Number of valence electrons = the number before the A

This is called Reactivity If an atom is not stable, it will want to get more electrons or give some electrons away to become like a nearby noble gas. This is called Reactivity Tell them – these are the chemical reactions that form compounds. They will learn more about how compounds are formed in high school.

Put these cards in a row: Comparing Reactivity Put these cards in a row: C N O F Ne Which of these is the least reactive? (Hint: which is stable?) Which of these do you think is the most reactive? Think, pair, share.

Comparing Reactivity The closer an element is to a noble gas, the more reactive it will be. Which is most reactive? C N O F Ne

These two groups are the most reactive because they are closest to the Noble Gases.

Practice

How many valence electrons are there in these atoms? 2; 4; 1; 1

Using the periodic table: How Many Valence Electrons? Hydrogen Aluminum Argon Sulfur Helium 1 Valence Electron 3 Valence Electrons 8 Valence Electrons 6 Valence Electrons 2 Valence Electron

Are these elements reactive or stable?

Which element is the most reactive… Aluminum or Chlorine? Chlorine

Which element is the most reactive… Sulfur or Phosphorus? Sulfur

Which element is the most reactive… Nitrogen or Neon? nitrogen

Which element is the most reactive… Sulfur, Chlorine or Argon? Chlorine

Which element is the most reactive… Nitrogen, Oxygen or Fluorine? fluorine