Alchemy Unit Investigation V!

Transcription

1 Alchemy Unit Investigation V! Lesson 3: Noble Gas Envy!

2 ChemCatalyst! An electron from a neutral lithium atom is transferred to a neutral fluorine atom. The lithium is left with a positive charge and the fluorine atom is left with a negative charge. The lithium and sodium atom are now attracted to each other.

3 ChemCatalyst! What happens to the charge on each atom? What type of bonding does this picture represent?

4 The Big Question! What ion charges are formed when atoms attain a noble gas electron configuration?!

5 You will be able to:! Predict what would have to happen for potassium to obtain a noble gas configuration.!

6 Purpose! Purpose: You will explore the ions that are formed when atoms give up and receive electrons from other atoms.!

7 Activity! You will be working in teams to create cards similar to the one on the right.! These cards will represent the ion charges for atoms in the periodic table.!

8 Activity! What information will help you identify which element the model of the atom represents?! Which circles represent the valence electrons?!

9 Activity! Fill in the name, symbol, and number of valence electrons found in the model atom.! Which shell is the valence shell?!

10 Activity! Chemists have found that many atoms are most stable (chemically unreactive) when the valence shell has either 0 or 8 electrons. (The first shell is stable with only 2 electrons) The goal is to get to either 0 or 8 valence electrons by adding to or removing the minimum number of electrons from the valence shell with the least amount of work.!

11 Activity! Would it be easier to add 3 electrons to nitrogen to get to 8 outer electrons or take away 5 electrons to reach 0?! To show the adding of 3 electrons, draw them in the outer ring!!

12 Activity! Now nitrogen has 8 valence electrons.! Cross out the 5 valence electrons and replace it with 8.! Circle gains and write 3 in the blank to show that you added 3 electrons.!! 3 8

13 Activity! magnesium Mg What element is represented by this card?! How many valence electrons does magnesium have?! What will be the easier to get to 8 or to 0?! How many valence electrons are left?! 2 2 0

14 Activity! The symbol for the ion is the same as the symbol for the element except it has the net charge written in the upper right hand corner.!

15 Activity! Charge = #protons - # electrons! If the #protons > # electrons then the net charge is positive and! if #protons < # electrons then the net charge is negative!

16 Activity! The symbol for nitrogen is N so the symbol for the ion will use N.! Since nitrogen gained 3 electrons to get 8 electrons in the valence shell, it now has 10 electrons total.! 7 protons 10 electrons = -3 charge!! N 3-

17 Copy the chart below! IA IIA IIIA IVA VA VIA VIIA C 4+ C 4- Si 4+ Si 4- Ge 4+ Sn 4+

18 Activity! Organize the cards according to the periodic table.! Fill in the chart with the ion symbols for the representative elements.! What kind of patterns can you see? Find at least three.

19 Activity! Explain how you can find how many valence electrons an atom has from the periodic table. How do the number of electrons compare to the number of protons in an neutral atoms? What happens to the charge on an atom when you remove electrons from an atom? Explain. What happens to the charge on an atom when you add electrons to an atom? Explain.

20 Making Sense! How reactive are noble gases? Why do you think noble gases don t add electrons to form negative ions easily? (Hint: what shell will the additional electron go?) Noble gases also don t lose electrons easily to form positive ions. What does that suggest about how strongly atoms with a filled valence shell hold on to their valence electrons?

21 Making Sense! Atoms with a positive charge are called cations. Cations are formed when electrons are lost from the valence shell, leaving the atom with more protons than electrons.! The symbol for a cation the symbol for the element and the charge of the cation written as a superscript in the upper right hand corner of the symbol: Example Ca 2+ and Na +.! Which elements tend to form cations?!

22 Making Sense! Atoms with a negative charge are called anions. Anions are formed when electrons are added to the valence shell, leaving the atom with more electrons than protons.! The symbol for a anion the symbol for the element and the charge of the anion written as a superscript in the upper right hand corner of the symbol: Example S 2- and Cl -! Which elements tend to form anions?

23 Notes The position of an element on the periodic table helps us to predict which ions of that element might be encountered in chemistry!

24 Notes! Noble gases are stable with 8 electrons in their filled valence shells. Atoms of metals tend to lose electrons to end up with the same number of valence electrons as a noble gas. Atoms of non-metals tend to gain electrons to end up with the same number of valence electrons as a noble gas. When atoms lose electrons, they have a positive charge and are called cations. When atoms gain electrons, they have a negative charge and are called anions.

25 Check-in How many valence electrons do each of the noble gases have (Except helium)? How many valence electrons do alkali metals tend to lose to form ions? Alkaline earth metals? How many valence electrons do halogens gain to form ions? Elements in the VIB (oxygen) family?!

26 Check-In! What kind of ion will Cesium form. Write its symbol. What is one kind of ion Tellurium might form. Write its symbol. What is one kind of ion Antimony might form. Write its symbol.