Packet 4: Bonding. Play song: (One of Mrs. Stampfel s favorite songs)

Transcription

1 Most atoms are not Packet 4: Bonding Atoms will, or share electrons in order to achieve a stable. Octet means that the atom has in its level. If an atom achieves a stable octet it will have the same electron configuration as. A is formed when atoms transfer or share electrons. They are forces that hold atoms together. Play song: (One of Mrs. Stampfel s favorite songs) There are two main types of chemical bonds: : bond formed when by the transfer of electrons from one atom to another. : bond formed when atoms share electrons. Energy and Bonding When a chemical bond is formed the product (resulting compound) has energy than the substances it was formed from. Because: energy is always when a bond is formed. It is an process. Ex: Cl + Cl Cl 2 + energy Compounds have than the atoms by themselves (they are more stable) When a chemical bond is the products have energy than the compound. Because: energy is always when bonds are broken. It is an process. Ex: Cl 2 + energy Cl + Cl The atoms by themselves have than the compounds (they are less stable)

2 Ionic Bonding When atoms gain or lose electrons they become. Metals form ions when they electrons. Nonmetals form ions when they electrons. Ex: Na and Cl Two types of ions: : (+) positive ions Anions: ( ) Na is the Cl is the Metals with, and electrons will lose electrons. Nonmetals with, and electrons wills gain electrons. The resulting compound is held together by charges of the ions through static electrical attraction. The overall charge of the compound is electrically because the number of electrons is EQUAL to the number of electrons. Ex: Li and F Click here for another enjoyable song:

3 Ionic Compounds are solid substances formed by ionic bonding. Characteristics of ionic solids: at room temperature, forming a lattice. melting and boiling points because of the strong attraction of ions. They conduct ONLY in liquid or aqueous form. This is due to the of the ions. They do not conduct in solid form. Check this out: (melting point of NaCl 1,474 F or 801 C) They in water. Lewis Electron Dot Structures for Ionic Bonding When drawing the electron dot structure for an ionic compound: Write electron dots symbols for both elements. Element on left loses. Element on right gains. Ex: After the metal loses its electrons it will have charge. The value of the charge is equivalent to the number of electrons lost by the metal atom (valence electrons). The nonmetal is written with dots and includes a charge. The value of the charge is equivalent to the number of electrons gained by the nonmetal atom. are generally placed around the negative ion, but are not mandatory. Ex: Practice Problems Draw Electron Dot Diagrams for the following ionic compounds: K 2 S Na 2 O MgS

4 CaBr 2 Al 2 O 3 KF Covalent Bonding Covalent bonds are formed when two atoms (both nonmetals) electrons. There is no transfer of electrons. Watch video and draw 2 examples: Electron sharing always occurs in pairs. Two atoms may share 1, 2, or 3 pairs of electrons forming: Single covalent bond: shared pair of electrons Ex: Double covalent bond: shared pairs of electrons Ex: Triple covalent bond: shared pairs of electrons Ex: The combination of atoms bound together by a covalent bond is called a. Molecules are electrically neutral. Ex:

5 Molecular Substances Molecular substances have the following characteristics: They can exist as solid liquid They are soft. They are conductors of heat and electricity because they do not have ions or moving electrons. They have melting and boiling points because of weak attraction between molecules. Ex: H 2 O, C 6 H 12 O 6, ( ), O 2 ( ) Types of Covalent Bonds: Covalent: when electrons are shared between atoms of the same element, the electrons are shared. Ex: all diatomic molecules (Say: BrINClHOF!) H 2 O 2 Polar : when electrons are shared between atoms of elements. The term polar means They are shared. The element with the higher will attract the electrons more strongly causing atom to have a partial negative charge Ex: HCl (H behaves like a group 17 element) H 2 O Electronegativity can be used to predict what types of bonds will form. Rule: 1. Go to Table S 2. Look up electronegativities for each element in compound

6 3. Take the DIFFERENCE between the two values. (subtract small number from big number: no negative numbers) 4. Determine whether it is ionic, polar or nonpolar covalent using the chart below Electronegativity Difference Bond Type 0.3 Nonpolar Covalent Between 0.4 and 1.9 Polar Covalent 2.0 Ionic The type of bond that is most polar is the bond. The smallest difference is the polar and the largest difference is the most polar. Sample Regents Problems using electronegativities: Which of the following bonds is the most polar in nature? (1) O 2 (2) HCl (3) NH 3 (4) HBr Work out: 2. In water, the bond between hydrogen and oxygen is (1) ionic, (2) polar covalent, (3) nonpolar covalent, (4) nonpolar noncovalent. 3. Which of the following is an example of a substance with a nonpolar covalent bond? (1) HCl (2) Cl 2 (3) HClO 2 (4) NaCl 4. The electronegativity of sulfur is (1) 16, (2) 239, (3) 2.6, (4) Which of the following bonds is most polar in nature? (1) Cl 2 (2) HI (3) HBr (4) NaCl 6. Which element has an atom with the greatest tendency to attract electrons in a chemical bond? (1) carbon (2) chlorine (3) silicon (4) sulfur Network Solids Network solids have covalent bonds between atoms linked into a giant network or one big.

7 Covalent bonds extend from one atom to another in continuous patterns, with no distinct molecules. Examples include, asbestos, graphite silicon carbide, silicon dioxide Propertites: They are They are conductors of heat and electricity They have (unlike covalently bonded substances) Coordinate Covalent Bonds In cases a coordinate covalent bond is formed when one donates electrons that are Ex: ammonium ion NH 4 + hydronium ion H 3 O + This is how most polyatomic ions are formed. See Reference Table E: Select Polyatomic Ions Polyatomic ions The atoms within a polyatomic ion are held together by bonds When polyatomic ions bond with metals, they form bonds Therefore, compounds containing polyatomic ions have both and bonds!

8 Ex: NaOH Ex: OH- Purple book page 40 Non-Chemical Bonds (or other ways stuff could be held together): Metallic Bonding Intermolecular Forces 1. Dipoles Polar Bonds Symmetrical Molecules Asymmetrical Molecules 2. Hydrogen Bonds 3. Dispersion Forces 4. Molecule-Ion Attraction Metallic Bonding Occurs in Ex: Cu, Consists of ions surrounded by a of mobile electrons Electrons belong to any atom in particular.

9 Properties of metallic bonding account for properties of metals: Good conductors of and as solids and liquid: because of electrons hard and ductile High and points (higher than nonmetals) see Table S Intermolecular Forces/Attractions Intermolecular attractions - forces of between that are not Dipoles Dipole - a molecule, or a molecule with an asymmetric, or unequal distribution of causing one end of the molecule to be while the other is negative dipole-dipole attraction - force of attraction between the positive end of one dipole and the end of another Polar Bonds/Molecules: Asymmetrical molecules (no symmetry): polar bonds and asymmetrical shape the molecule is POLAR Ex: H 2 O Ex: NH 3 Ex: HCl Overall charge is uneven making molecule POLAR. Symmetrical molecules with polar bonds are overall NONPOLAR : Ex: CO 2 Ex:CH 4 Overall charge is even making molecule NONPOLAR

10 Hydrogen bonding: Intermolecular force linking that is covalently bonded to a small electronegative element such as, or fluorine, to another electronegative element of the same or another molecule. This is the type of force that holds together!! Accounts for the relatively high boiling point of water. Ex: H 2 O much higher than H 2 S. Other compounds with hydrogen bonding: and HF Dispersion Forces: Very force between molecules and gases such as diatomic (say: BrINClHOF) and gases. Force increases with increase atomic/molecular size. Therefore, boiling point with increase in size of element or molecule. As you go down Group 17 or 18 boiling point.

11 Molecule-Ion Attraction: Attraction between of an ionic compound (such as salt) of and molecules. Common formulas that contain molecule-ion attraction: Practice Regents Questions 1. Which substance exists as a metallic crystals (1) Ar (3) SiO 2 (2) Au (4) CO 2 2. Mobile electrons are a distinguishing characteristic of (1) an ionic bond (2) a metallic bond (3) an electrovalent bond (4) a covalent bond 3. Which kinds of bonds are found in a sample of H2O(s)? (1) hydrogen bonds, only (2) covalent bonds, only (3) both ionic and hydrogen bonds (4)both covalent and hydrogen bonds 4. Which substance is made up of molecules that are dipoles? (1) N 2 (3) CH 4 (2) H 2 O (4) CO Which element consists of positive ions immersed in a "sea" of mobile electrons? (1) sulfur (2) calcium (2) nitrogen (4) chlorine Intermolecular Forces and Vapor Pressure See Reference Table H Low vapor pressure is due to holding the molecule together. High vapor pressure is due to molecules can easily become a gas or vapor. High vapor pressure= intermolecular force.

12 Sample questions: The vapor pressure of water at 100ºC is. Ethanoic acid has vapor pressure of at 50 ºC. The substance with the weakest intermolecular force is More vapor pressure questions:

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