Chemical Bonding A bond is when 2 or

Chemical Bonding A bond is when 2 or more atoms combine to: 1. Lower their energy 2. Become more stable

Covalent Bonds • A covalent bond is a bond in which the atoms share electrons in an overlapping manner. • They are formed between two nonmetals. • There are two types of covalent bonds: polar and non-polar.

Non-polar Covalent Bonds • A non-polar covalent bond is a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge.

Non-polar Covalent Bonds • Examples of non-polar covalent bonds are the diatomic elements. (the “gen” series) • H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

Polar Covalent Bonds • A polar covalent bond is a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons.

Covalent Bonds • One way to tell the difference between a polar and non-polar covalent bond is by the electronegativities. If the electronegativities are equal the compound is non-polar. If the electronegativities are not equal the compound is polar.

Covalent Bonds • Another way to tell a difference between a polar and non-polar molecule is if a molecule is symmetrical, its non-polar and if it isn’t, it is polar. • Water is a polar molecule.

Covalent Bonds • Molecules can be held together by single, double, or even triple covalent bonds. • In a single bond the atoms share 2 electrons. • In a double bond the atoms share 4 electrons. • In a triple bond the atoms share 6 electrons.

Ionic Bonding • An ionic compound is composed of a positive and a negative ions that are combined so that the number of positive and negative charges are equal. • Ionic bonds are formed usually formed between metals and nonmetals.

Ionic Bonding • Example: Na. Cl

Bonding • One way to tell if a compound is covalent or ionic is by the electronegativities of the atoms. If you subtract the electronegativities of both atoms and you come out with 0. 0 – 1. 7, it is a covalent bond. If you come out with 1. 7 -4. 0, it is a ionic bond.

Bonding • Example: HCl: H has a electronegativity of 2. 5 Cl has a electronegativity of 3. 2 Therefore it is a polar covalent molecule.

Polyatomic Ions • A polyatomic ion is a compound of two or more covalently bonded atoms with a charge. • These ions are found on reference table E. • Examples: OH-, NH 4+,

VSEPR Theory • Valence Shell Electron Pair Repulsion Molecule Type Example Shape AB 2 Be. F 2 Linear AB 3 BF 3 Trigonal planar AB 4 CH 4 Tetrahedral AB 3 E NH 3 AB 2 E Sn. Cl 2 Trigonal pyramid Bent AB 2 E 2 H 2 O Bent

Metallic Bonding • Metallic bonding is the chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons.

Intermolecular Forces of Attraction (Van Der Waals Forces) Intermolecular forces are the forces of attraction between molecules.

Dipole-Dipole Forces • The forces of attraction between polar molecules are known as dipole-dipole forces.

Hydrogen Bonding • Hydrogen bonding is a very strong dipole-dipole attraction that only occurs between hydrogens and small electronegative atoms such as nitrogen, oxygen, and fluorine. • One example is water.

London Dispersion Forces • London Dispersion forces are forces that hold non-polar molecules together. • Some examples are the diatomic elements.

Network Solids • A network solid is an strong on going link of non-polar covalent bonds. • Examples: – Diamonds – Silicon – Sand (Si. O 2) – Si. C (used for computer chips)

Bonds Non-polar Polar Ionic Metallic Forces of Attraction London Forces Dipole-Dipole Hydrogen Bonding Ionic Solids Network Solids Bonds and forces are listed from the weakest to the strongest.

Chemical Bonding Review Questions

1) Which bond has the greatest degree of ionic character? a) I-Cl b) Cl-Cl c) H-Cl d) K-Cl Answer: D

2) Which compound contains ionic bonds? a) HBr b) Na. Br c) C 6 H 12 O 6 d) CO 2 Answer: B

3) A characteristic of ionic solids is that they: a) Have low boiling points b) Are noncrystalline c) Conduct electricity d) Have high melting points Answer: D

4) Which substance will conduct electricity in both the solid phase and the liquid phase? a) H 2 b) Ag c) HCl d) Ag. Cl Answer: B

5) A substance that has a melting point of 1074 K conducts electricity when dissolved in water, but does not conduct electricity in a solid phase. The substance is most likely: a) A molecular solid b) An ionic solid c) A network solid d) A metallic solid Answer: B

6) A molecule of ammonia (NH 3) contains: a) Covalent bonds, only b) Both covalent and ionic bonds c) Neither covalent and ionic bonds d) Ionic bonds, only Answer: A

7) The correct electron dot formula for hydrogen chloride is: a) H Cl b) H Cl c) H Cl d) H Cl Answer: C

8) Which formula represents a tetrahedral molecule? a) Ca. Cl 2 b) Br 2 c) CH 4 d) HBr Answer: C

9) Two atoms of element A unite to form a molecule with the formula A 2. The bond between the atoms in the molecule is: a) Polar covalent b) Non-polar covalent c) Electrovalent d) Ionic Answer: B

10) What type of bonding is found in the molecule HBr? a) Non-polar covalent b) Polar covalent c) Ionic d) Metallic Answer: B

11) Which type of bond is contained in a water molecule? a) Polar covalent b) Electrovalent c) Ionic d) Non-polar covalent Answer: A

12) Which molecule is a dipole? a) HCl b) CH 4 c) H 2 d) N 2 Answer: A

13) Which structural formula represents a non-polar symmetrical molecule? a) b) c) d) Answer: B

14) The strongest hydrogen bonds are formed between molecules of: a) H 2 Te b) H 2 S c) H 2 O d) H 2 Se Answer: C

15) Which kind of bonds are found in a sample of H 2 O? a) Both covalent and hydrogen bonds b) Both ionic and hydrogen bonds c) Hydrogen bonds, only d) Covalent bonds, only Answer: A

16) Which of the following noble gases has the lowest normal boiling point? a) Kr b) Ne c) Xe d) Ar Answer: B

17) Which type of bonding accounts for the unusually high boiling point of water? a) Network bonding b) Covalent bonding c) Van der Waals forces d) Hydrogen bonding Answer: D

18) The attraction which exists between carbon dioxide molecules in solid carbon dioxide is due to a) Ionic bonds b) Hydrogen bonds c) London Dispersion Forces d) Molecule-ion forces Answer: C

19) Helium may be liquefied at low temperature and high pressure primarily because of a) London Dispersion Forces b) Hydrogen bonding c) Covalent bonds d) Ionic attraction Answer: A

20) Van der Waals forces of attraction between molecules decrease with a) Decreasing # of electrons and increasing distance between the molecules b) Increasing # of electrons and decreasing distance between the molecules c) Decreasing # of electrons and decreasing distance between the molecules d) Increasing # of electrons and increasing distance between the molecules Answer: A

21) Molecule-ion attractions are found in: a) KBr (s) b) CO (g) c) Na. Cl (aq) d) Cu (s) Answer: C

22) Which formula represents a molecular solid? a) Na. Cl b) Cu c) C 6 H 12 O 6 d) KF Answer: C

23) Which compound is a poor conductor of heat and electricity and has a high melting point? a) H 2 O b) CO 2 c) Si. O 2 d) N 2 O Answer: C

24) What type of bonds are present in a strip of magnesium ribbon? a) Van der Waals b) Metallic c) Ionic d) Covalent Answer: B

25) Which substance contains positive ions immersed in a sea of mobile electrons? a) Cu. O b) Si. O 2 c) Cu d) O 2 Answer: C

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