Chemical Bonding

2. Chemical Bonding Why on Earth Do Elements Do It?

3. Q: Why do atoms combine to form compounds? A: Atoms combine to form compounds in order to become chemically stable.

4. Q: What makes an atom chemically stable? A: An atom is chemically stable when it has a full valence shell.

5. Q: How do atoms get a full valence shell? A: An atom will get a full valence shell by gaining, losing, or sharing one or more electrons. These electrons come from other atoms that are also “trying” to become chemically stable.

6. Q: Are there any elements that do not gain, lose, or share electrons with other atoms? If so, what are these elements and why don’t they gain, lose or share electrons? A: Yes, the noble gases are already chemically stable, so there is no reason for them to change their number of valence electrons.

7. Q: What happens when atoms gain, lose or share valence electrons? A: When atoms gain, lose or share electrons, a chemical change occurs, and chemical bonds are formed between the atoms. The lines in this model represent chemical bonds that hold the different atoms together.

8. Q: What is a chemical bond? A: A chemical bond is a force that holds together atoms or ions in a compound. Just like the way magnets can hold each other in place!

9. Q: What are the two main types of chemical bonding? A: The two types of chemical bonding are ionic bonding and covalent bonding. http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf

11. Q: What happens during ionic bonding? A: During ionic bonding, one or more atoms will give up one or more electrons. Another atom or atoms will take the electrons. As a result, all of the atoms involved will become chemically stable. These particles will now also have an electrical charge. The attractive force between positively and negatively charged particles is the ionic bond that holds the new compound together.

12. Q: How can you determine the charge on a particle after it has gained or lost electrons? A: When an atom losesx electrons, it gets a charge of +x. When an atom gainsx electrons, it gets a charge of –x. For example, calcium will lose 2 electrons, so it gets a charge of +2. Nitrogen will gain 3 electrons, so it gets a charge of –3.

13. Q: What are positively and negatively charged particles called? A: Charged particles are called ions. Ions with a positive charge are called cations, and ions with a negative charge are called anions.

14. Q: Use Lewis Dot Diagrams to show how atoms of the following elements form ionic compounds: • lithium and fluorine • beryllium and oxygen • sulfur and sodium • magnesium and chlorine • oxygen and aluminum Can you identify the cation and the anion in each pair?

16. Q: What happens during covalent bonding? A: During covalent bonding, one or more atoms will share one or more electrons with other atoms. This results in the formation of a molecule.

17. Q: What are the two types of covalent compounds? A: The 2 types of covalent compounds are polar covalent and non-polar covalent compounds.

18. Q: What is the difference between polar and non-polar covalent compounds? A: In a polar covalent compound, the atoms share the electrons unequally, so the electrons spend more time around one end of the molecule and less time around the other end. This results in the molecule having one end that has a slight negative charge and one end that has a slight positive charge. In a non-polar covalent compound, the atoms share the electrons equally, so the electrons spend equal time around each atom. This means the molecule does not have a positive or negative end.

19. Q: Use Lewis Dot Diagrams to show how the atoms in the following covalent molecules share their electrons. • H2♦ O2 • N2♦HCl • H2O ♦ CO2 • CH4♦ Cl2

20. Q: How can you tell if two elements will form an ionic bond or a covalent bond? A: In general, if one of the elements is a metal and one is a non-metal, the bond will be ionic. If the elements are both non-metals, the bond will usually be covalent. We will not deal with any cases of 2 metals bonding together.

21. Q: What are “naturally occurring diatomic molecules”? List the 7 elements that are like this. What kind of molecules are these—ionic, polar covalent, or non-polar covalent?

22. A: Naturally occurring diatomic molecules are elements that are only found in nature as a molecule made up of 2 atoms of that element. The 7 elements that are like this are: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine (i.e. H2, N2, O2, F2, Cl2, Br2, I2). These molecules are non-polar covalent because the 2 atoms pull equally on the shared electron(s).

23. Q: What is a polyatomic ion? A: A polyatomic ion is an ion (charged particle) that is made of 2 or more atoms.

24. Q: You should be able to list the name, formula, and charge for each of the following polyatomic ions: NameFormulaCharge ammonium NH4 +1 acetate C2H3O2 -1 chlorate ClO3 -1 hydroxide OH -1 nitrate NO3 -1 carbonate CO3 -2 sulfate SO4 -2 phosphate PO4 -3

25. Oxidation Numbers • Oxidation Number— a positive or negative number assigned to an element to show its combining ability in a compound. • Shows how many electrons an atom gains, loses, or shares when bonding with other atoms. • Ox. #’s are typically a periodic (repeating) property.

26. Examples: • Lithium  +1 • Calcium  +2 • Aluminum  +3 • Carbon  +/- 4 • Nitrogen  -3 • Sulfur  -2 • Iodine  -1 • Transition metals have variable ox. #’s

27. A few of the transition metals and their possible oxidation #’s: • Fe +2 or +3 • Cu +1 or +2 • Pb +2 or +4 • Cr +2 or +3 Learn these!