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Chemical Bonding The chemical properties of elements depend on an element’s electron configuration. When the highest occupied energy level of an atom is.

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Presentation on theme: "Chemical Bonding The chemical properties of elements depend on an element’s electron configuration. When the highest occupied energy level of an atom is."— Presentation transcript:

1 Chemical Bonding The chemical properties of elements depend on an element’s electron configuration. When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. That highest energy level is called the valence level and the electrons that occupy it are called valence electrons, therefore the chemical properties of elements depend on their valence electrons.

2 Electron Configueration

3 No Coincidences in Science! 
s – 2 p – 6 d – 10 f - 14 No Coincidences in Science! 

4 Chemical Bonding Elements with incomplete sets of valence electrons tend to react….what number indicates a complete valence level? Some elements achieve stable electron configurations by transferring electrons between atoms. Each atom ends up with a more stable arrangement than it had before the transfer.

5 Chemical Bonding The oxidation number is the number of electrons that an atom of an element has to gain or lose to become stable. **This becomes important later!** Li +1 O -2

6 Oxidation Numbers What are the oxidation numbers for the following ions? Ca As Rb F S Na Al Cl O If the element NEEDS electrons, the oxidation number is NEGATIVE. If the element has EXTRA electrons to give away, the oxidation number is POSITIVE.

7 Ions When an atom gains or loses electrons, the number of protons and electrons is no longer equal….the atom is no longer neutral. Atoms that have a net positive or negative charge are called ions. Negatively charged ions are anions. Positively charged ions are cations.

8 Chemical Bonding When an anion and a cation are close together, a chemical bond can form between them. A chemical bond is the force that holds atoms or ions together as a unit. Dogs Teaching Chemistry: Chemical Bonds Video  (In Phys Sci Video File)

9 Ionic Bonding An ionic bond is the force that holds cations and anions together. The energy needed for one atom to take an electron from another atom, forming a cation, is called ionization energy. The atom that had a higher electronegativity becomes an anion, and the atom that had a lower electronegativity (did not hold its electrons very tightly) became the cation

10 Electronegativity Increasing Electronegativity

11 Ionic Bonding Compounds formed through ionic bonds are called ionic compounds and form in very specific ratios. Ex: For every single Na atom in salt, there will ALWAYS be one atom of Cl.

12 Ionic Bonding Because ionic bonds form cations and anions, you end up with ionic compounds that have positive ‘ends’ and negative ‘ends’ or in many cases ‘points’ if the compound is many sided. These charged areas attract neighboring molecules and cause them to link up in very specific arrangements, so solids formed of ionic compounds forming a lattice structure called a crystal.


14 Ionic Bonding Properties of ionic compounds reflect the very strong bonds among ionic compounds. High melting point Solids shatter Solids are poor conductors of electricity Liquids are great conductors of electricity because the ions are free to move around

15 Naming Ionic Compounds
In naming ionic compounds: When the compound contains only two elements, you write the name of the cation first and the anion second, changing the ending of the anion to –ide. Ex: A compound made up of sodium and chlorine would be written sodium chloride. What would oxygen (O) and potassium (K) be called?

16 Naming Ionic Compounds
Some of the transitional metals form more than one type of cation. The name of the ion contains a Roman numeral to indicate the charge Example: Copper has 2 ions – Cu(I) and Cu (II) Cu(I) has an oxidation number of 1+ Combine it with O 2- and you would get…. Cu(II) has an oxidation number of 2+

17 Naming Ionic Compounds
Sometimes groups of covalently bonded atoms act as a unit and have a negative or positive charge (they either gained or lost electrons during the bonding process and have an unequal total number of protons and electrons now)….so they now still need to either gain or lose one or two (in some cases 3) electrons to become stable. These groups of atoms that act as a single unit, with a charge are called polyatomic atoms.

18 Notice that most of these polyatomic ions are anions
p. 173 in book Notice that most of these polyatomic ions are anions You don’t need to change the ending of the polyatomic anions when naming compounds that contain them.

19 Naming Ionic Compounds
Name the following….. Iodine and magnesium Iron (II) and phosphorus Sulfite and potassium Permanganate and silver Sodium and chlorine Nitrate and ammonium

20 Ionic Formulas A chemical formula shows what elements the compound contains and how many atoms of each element. Ex: NaCl has one atom of each (you don’t have to write the number 1, it is implied) Ag2O has 2 atoms of silver and 1 atom of oxygen

21 Ionic Formulas The formula tells you which elements are present in the ionic bond, and the ratio of atoms or ions of these elements. How do you know how many atoms of one element or ion you need to bond with the atoms of another? MATH – BWAAHAAHAAHAAHAAAAA! No, just use the oxidation numbers! 

22 ***You must keep the entire polyatomic ion in parenthesis***
Ionic Formulas First, write the symbols, cation first, with the appropriate oxidation numbers, then crisscross the oxidation numbers as subscripts as the opposite element’s (or polyatomic ion) If the numbers are multiples, you reduce (i.e., 2 and 4 reduce down to 1 and 2) You don’t have to write a 1 – it is understood ***You must keep the entire polyatomic ion in parenthesis***

23 Ionic Formulas Criss-cross applesauce……Start with Basics…..
Examples: K and S; Al and F Now you: Li and N; Mg and Cl; Na and P; B and O Ex: Magnesium and Phosphorus Mg2+ and P3- Ex: Sodium and Hydrogen phosphate Na1+ and (HPO4)2- Ex: Ammonium and Nitrogen (NH4)+ and N3-

24 Covalent Bonding An electron dot diagram is a model of an atom showing only the valence electrons. Electron dot diagrams show only the valence electrons, not all of the electrons of atoms of an element. Very helpful when showing covalent bonds.

25 Covalent Bonding Ex: H O H
When none of the atoms will give up electrons in order to make a bond, atoms may share pairs of electrons instead, forming a covalent bond. They MUST SHARE IN PAIRS. The resulting molecule is a neutral group of atoms that are joined together by one or more covalent bonds. The attractions between the shared electrons and the protons in each nucleus hold the atoms together. Ex: H O H

26 Covalent Bonding In a molecule, electrons are not always shared equally. Covalent bonds in which the electrons are shared equally are called nonpolar covalent bonds, and form nonpolar molecules. Covalent bonds in which the electrons are NOT shared equally are called polar covalent bonds, and may form polar OR nonpolar molecules. In a polar covalent bond, the atom that has the higher electronegativity will have a partial negative charge; the atom with the lower electronegativity will have a partial positive charge.

27 Electronegativity Increasing Electronegativity

28 Covalent Bonding Capillary Action----

29 Covalent Bonding δ δ δ

30 Covalent Bonding Attractions between polar molecules is stronger than attractions between nonpolar molecules.

31 Covalent Bonding Just because the covalent bonds that hold a molecule together are polar, does not mean that the resulting molecule is polar…. If there are only two atoms, then it will be polar. If there are more than two atoms, it depends on the type of atoms and the shape of the molecule.

32 Molecular Names The name and formula of a molecular compound describe the type and number of atoms in a molecule. The general rule is that the most metallic elements are listed first – farthest to the left. If they are in the same column, the one closest to the bottom is listed first. The second element is changed to end in the suffix –ide. Use prefixes (p.175 in book) to indicate how many atoms of each element you have. Water’s is made up of 2 H atoms and 2 O atoms = dihydrogen monoxide.

33 Molecular Formulas To write the formula, write the symbol for each of the elements you have named, and take the prefix and change it to numeral form and place it as a subscript after the symbol Ex: dihydrogen monoxide = H2O

34 Chemical Bond So HOW DO YOU KNOW WHAT TYPE OF BOND WILL FORM BETWEEN DIFFERENT ELEMENTS? It all goes back to the electronegativity of the elements involved. Electronegativity is just how strongly an element’s atoms wants their electrons – the higher the electronegativity, the harder it is to remove the electrons. Practice: NH3 So take the elements you are looking at, and find the difference between their two electronegativity numbers. 0-0.5 – a non-polar covalent Bond will generally form , a polar covalent bond will generally form Over 1.7, an ionic bond will generally form

35 Electronegativity Increasing Electronegativity

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