Remember the octet rule: Atoms will work to achieve a full valence shell of electrons:

Transcription

1 Remember the octet rule: Atoms will work to achieve a full valence shell of electrons:

2 The first type of sharing is IONIC. This occurs when electrons are given up by one atom and taken by another. This occurs between metals and non-metals. The second type of sharing is COVALENT. Electrons are shared in a covalent bond. This occurs between either metals and metals or non-metals and non-metals. The third type of sharing is METALLIC. Electrons are freely shared, without pattern. This only occurs among metals.

3 The same Lewis Dot Structures used to represent valence electrons can be used to show bonding between atoms as well. A sodium gives up an electron, becoming positively charged. Chlorine takes the electron, becoming negatively charged.

4 + - The positive ion in an ionic compound is called a The negative ion in an ionic compound is called an CATION Cat-eye-on ANION Ann-eye-on Determines the strength of attraction of one atom to another atom s electrons. Chlorine has high electronegativity; sodium s is low. Chlorine can therefore pull away sodium s electrons.

5 Creating Ionic Formulas NaCl is known widely as table salt; however, its scientific name is Sodium chloride. In order to learn the scientific name of a compound, you must remember a few things: 1. The charges of the atoms in an ionic bond must add up to zero. 2. The atoms in an ionic bond must have full valence shells by the end of the process.

6 Creating Ionic Formulas What happens if we try to make a compound of Lithium and Nitrogen? Therefore, the CHEMICAL FORMULA for Lithium Nitride is Li3N

7 SHORTCUT!!! Instead of drawing Lewis dot Structures, or counting out ion charges when trying to figure ionic bonds, try this little shortcut: Determine the charge each atom takes as an ion- then SWITCH the numbers! Then SWITCH---

8 Naming Ionic Compounds Ionic compounds are quite easy to name: 1. Begin with the cation (metal) name, normal. Lithium Add the anion s name, but alter the ending Nitride Say it: Lithium Nitride

9 Exceptions for Naming Ionic Compounds Polyatomic ions do not undergo any name change when in compound- so don t add the -ide ending to a polyatomic ion. Transition metals are another exceptionthey can form ions with different charges!

10 Most of the transition metals can form multiple ions; however, we will only use four of them in this class: For most transition metals, there are two possible ions that can form. For the one with the smaller charge, we use the -ous suffix. For those ions with larger charges, we use -ic as an ending. But we must also use the Latinized name of the metal. Copper = Cu = Cuprous (+1) and Cupric (+2) Iron = Fe = Ferrous (+2) and Ferric (+3) Lead = Pb = Plumbous (+2) and Plumbic (+3) Tin = Sn = Stannous (+2) and Stannic (+4)

11 Naming Transition Metals in Compounds When naming compounds containing transition metals, you must include the charge of the ion in order to be able to have the correct compound. What s the difference in these two compounds?

12 General Characteristics of Ionic In GENERAL, ionic compounds: Compounds

13 Covalent Bonding Co- means shared, or along with; -valent means valence shell electrons; so Covalent means shared valence electrons. If the ELECTRONEGATIVITY of an element, paired with another, is less than 1.8, we get COVALENT compounds. The Cheater s Way: If you have a non-metal plus a non-metal, there is a 99% chance you have a covalent compound.

14 Creating Covalent Compounds Unlike ionic compounds, there is no way to tell a covalent compound s makeup simply by giving you the atoms involved. A way of gauging the amount of sharing going on in a covalent compound.

15 Oxidation States There are 3 rules to remember when determining oxidation states:

16 Oxidation States Using those three rules, oxidation states can be determined for covalent compounds. For example, nitrogen can form many compounds with oxygen; here are a few- figure out the oxidation state of each element in the compounds: N2O NO N2O4 N2O2 NO2 N2O5

17 Naming Covalent Compounds In order to differentiate among covalent compounds, we must use Latin numerical prefixes. 1= mono 2= di 3= tri 4= tetra 5= penta 6=hexa 7= hepta 8= octa 9= nona

18 Naming Covalent Compounds In order to name covalent compounds, we have to look at the compounds as individual elements once again. If the first element is a single atom, then simply say the element name, as before. Use prefixes for all other elements in the compound. If the first element is a multiple atom, then use prefixes. Use prefixes for all other elements in the compound.

19 Qualitative Analysis Qualitative Analysis is the use of tools to determine what elements are in a compound. The data from Qualitative Analysis will give us an EMPIRICAL FORMULA, or a list of the elements in a compound in their simplest ratio. Some tools chemists use for Qualitative Analysis: Spectrometer; Acids; Bases; Fire; Balances An example of an Empirical formula is: CH2O

20 Quantitative Analysis Quantitative Analysis can be used to determine the exact number of molecules or atoms in a substance. This information will give us Molecular formulas for compounds, which represent the actual amount of atoms in a single molecule. Tools a chemist use for Quantitative Analysis include a Mass Spectrometer, Bell Jars (gas volumes), analytical balances, and so on. An example of a molecular formula would be: C6H12O6 (glucose)

21 Dr. Hofbrincl to the Maternity Ward... Certain elements are always found in pairs in nature; this will teach us to draw structural formulas. These elements are: H, O, F, Br, I, N, Cl Or, Dr. HOFBrINCl and since they are always in pairs- Dr. HOFBrINCl delivers twins

22 Special Covalent Situations Multiple Bonds: Sometimes it is necessary for there to be multiple bonds in order to fill a valence shell (O2, N2) Hybrid Orbitals When Carbon forms bonds, it has the ability to bond in fours places- but because the p orbitals are outside of the s orbital, the s orbital would be blocked from bonding.

23 VSEPR Theory and Molecular Shapes By knowing that electrons repel each other, we can predict the shape of molecules. When we draw Lewis Dot Structures, we draw the electrons at 90 degrees from each other since they repel each other Kernel

24 VSEPR Theory... Due to sharing of electrons, repulsion can be changed, altering the shape of molecules. We will be concerned with 5 shapes of molecules; each has different bond angles, giving each a unique shape. Linear angle Pyramidal -109 angle Bent 90 - angle Tetrahedral -109 angle Triagonal Planar -120 angle

25 Molecular Shapes Any two-atom molecule will show up as a straight-line molecule. Atom Bond 1,2,or 3 Atom Molecules with three atoms and only two bonds will be bent if there are two extra electrons. Atom Single bonds only! Atom Atom

26 A More Shapes A A Triagonal Planar- Occur when 4 atoms are bonded together with NO EXTRA electrons. A This is a FLAT SHAPE! These shapes occur when there are 4 atoms bonded together, but with extra electrons. Unshared electronsthese push harder than the shared pairs This is a 3- dimensional shape! Farther away

27 Tetrahedral Shape All 5-atom molecules will take on a tetrahedral shape. A Carbon-family atom must be the central atom for a tetrahedron. They are the only atoms that can form 4 bonds. Farther Away

28 Polar and Non-Polar Molecules When atoms combine, there is a chance they will have different electronegativities, but still won t be an ionic compound. If the electronegativity difference between molecules is greater than 0.9, we have a polar molecule- that is, the molecule will have a slightly positive side, and a slightly negative side.

29 Polarity The term polar means having two opposite ends, or sides. Carbon Fluorine Carbon has an electronegativity of 2.6; Fluorine is 4.0. The difference between them is 1.4, clearly polar. Fluorine clearly has a greater attraction for electrons than carbon, and therefore, will pull carbon s electrons closer to it.

30 Polarity Continued If ions are shown with + and - signs, polarity, which also denotes a positive and negative charge, but a small change, we can show those states with a lower-case delta, a Greek letter. Upper-case delta stands for a change; lower case, then, means a small change. Carbon Fluorine

31 Non-Polar Molecules Anytime that an atom has an electronegativity difference of less than 0.9, that bond is non-polar. It can be represented with a 0 above it, meaning there is a charge of zero on the atoms. Nitrogen Oxygen Nitrogen= 3.1; Oxygen= 3.5; = 0.4; Non-Polar

32 Multiple-Atom Compounds and Polarity Some compounds have more than two atoms, and yet still may be polar or non-polar. In order to determine polarity of these types of compounds, you must consider not only electronegativity, but also the SHAPES of molecules. Consider the case of CH3Cl- there are 5 atoms, and three different types, each type with different electronegativities. Cl C H H H

33 More Polarity... Cl C Chlorine, 3.2, - Carbon, 2.6= 0.6; non-polar. Carbon, 2.6- Hydrogen, 2.2= 0.4; non-polar. So IS this a non-polar molecule? H H H And here s why- Draw an arrow from atoms with low electronegativity towards atoms with higher electronegativity, and you will see a distinct pattern form...

34 Still More polarity... The direction the arrows point show the direction that the electrons will move; when all the electrons move away from one end, and towards another, we have a polar molecule. Cl C We should now add our symbols to show polarity. H H H

35 Metallic Bonds Occur among Metals and: 1. Accounts for conductivity, malleability, and ductility. 2. Generally more effective the more BACKFILLED e- there are in an atom. = Metal Atom = Electron Any e- can move freely throughout the metal atoms