MOLECULAR COMPOUNDS. Example: CO 2, not O 2 C

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1 LEARNING GOAL: GIVEN THE FORMULA OF A MOLECULAR COMPOUND, WRITE ITS CORRECT NAME; GIVEN THE NAME OF A MOLECULAR COMPOUND, WRITE ITS FORMULA.

2 Two atoms can be held together by their mutual attraction for electrons they share in a covalent bond. A substance made up of atoms which are held together by covalent bonds is a covalent compound. A molecule is any group of atoms held together by covalent bonds.

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4 Nonmetal atoms, and a few metalloids, form covalent bonds, with the exception of the noble gases as they typically do not form compounds due to their full valence shells.

5 The chemical formula for a covalent compound uses symbols and subscripts just like ionic compounds. The subscripts indicate the number of atoms of each element used to form the compound. Usually, the elements, except for H, are written in order of increasing group number. Example: CO 2, not O 2 C

6 NH3 CH4 Si2O BF3

7 The term covalent refers to the sharing of valence electrons.

8 Bonding pairs of electrons are those electrons found in a single covalent bond. One electron comes from one of the atoms taking part in the covalent bond; the other electron comes from the other atom taking part in the bond.

9 Nonbonding pairs of electrons are those electrons that exist in the valence shell of an atom but are not part of the covalent bond.

10 In a nonbonding pair, both electrons come from the same atom. Nonbonding pairs are also known as lone pairs.

11 It is possible to have more than two electrons shared between two atoms in multiple covalent bonds.

12 A double covalent bond occurs when four electrons are shared between two atoms. There are two bonding pairs of electrons in a double covalent bond. A double covalent bond is abbreviated with the term double bond.

13 A triple covalent bond occurs when six electrons are shared between two atoms. There are three bonding pairs of electrons in a triple covalent bond. A triple covalent bond is abbreviated with the term triple bond.

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15 Multiple bonds, like a quadruple covalent bond, are not commonly observed.

16 A triple bond is stronger than a double bond, which is stronger than a single bond.

17 Multiple covalent bonds are frequently observed in diatomic molecules. Diatomic molecules contain two like atoms.

18 Many nonmetals exist in their natural state as diatomic molecules as this provides the atoms a stable electron arrangement. The elements that are diatomic in their natural state include H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2.

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20 The naming of a binary covalent compound made of only two types of elements involves the use of prefixes. The names need prefixes because several different compounds can form from the same two nonmetals.

21 The first nonmetal in the compound is named by its elemental name. The second nonmetal in the compound is named by using the first syllable of its elemental name with the ending changed to ide.

22 Subscripts that indicate two or more atoms of an element are expressed as prefixes placed in front of each name. mono di tri tetra penta hexa hepta octa nona deca

23 The prefix mono- is omitted from the first nonmetal in the name. When adding a prefix and the vowels o and o or a and o appear together, the first vowel is omitted from the prefix.

24 Writing a chemical formula from the name of a covalent compound is easily done by following these two steps: Write the symbol of the element for each nonmetal in order as they appear in the name. Convert the prefixes of the names into subscripts.

25 dinitrogen tetroxide dichlorine heptoxide silicon tetrafluoride SO 3 P 4 O 10