Question 1: 

Answer the following questions:

1. Arrange these compounds in order of increasing ionic character of their bonds: LiF, LiBr, KCl, KI                                                                               
2. Classify each of the bonds as either ionic or covalent.  
3. What force holds the two ions together in an ionic bond?              
4. What is the meaning of the oxidation number of an element that forms an ionic bond?          

           

1. What is a molecule?                    

           

1. How are molecules and polyatomic ions alike? How are they different?

Question 2: ( 4 marks,1 for each)

What levels of structure organization are possible for proteins and what do these each describe? 

 

Qn. 1

a)

You find the difference in the electronegativities of the elements and then order them from least to greatest as follows;

LiF = 3, LiBr = 1.98, KCl = 2.34, KI = 1.84.

Therefore the arrangement  in order of increasing ionic character  is;

KI, LiBr, KCl, LiF

b)

All the compounds ( LiF, LiBr, KCl, KI) have an ionic bond

c)

Ions in an ionic bond are held together by electrostatic force. Electrostatic attraction is the attraction between atoms that have opposite charge and holds the atoms together in ionic bonds.

d)

An oxidation number of an element that forms an ionic bond refers to a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction.

e)

A molecule refers to a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.

f)

How molecules and polyatomic ions are alike

• Atoms that are covalently bonded within a molecule are held together by pairs of electrons that are shared between two atoms.
• In a similar case, the atoms that make up a polyatomic ion are also covalently bonded, or held together by shared pairs of electrons.
• In both molecules and polyatomic ions, the atoms are separated from each other when a chemical reaction takes place.

How molecules and polyatomic ions are different 

•  Molecules are electrically neutral while polyatomic ions have a net charge. In the process of the ion forming one or more electrons are either gained or lost. Most polyatomic ions have an excess of electrons and are therefore are negative.
• Molecules exist as molecular compounds, which generally have low melting and boiling points because attractions between individual molecules are weak. Polyatomic ions exist in ionic compounds. A polyatomic ion is attracted to one or more oppositely charged ions, forming a compound that exists as a crystal lattice of repeating positive and negative ions. Ionic compounds have high melting points because a lot of energy is needed to overcome the strong attraction between positive and negative ions.

Qn. 2

A protein's primary structure is defined as the amino acid sequence of its polypeptide chain.

Levels

• Primary structure. This refers to the sequence of amino acids in the polypeptide chain
• Secondary structure. This is the local spatial arrangement of a polypeptide's main chain atoms
• Tertiary structure. This refers to the three-dimensional structure of an entire polypeptide chain.
• Quaternary structure. This is the three-dimensional arrangement of the subunits in a protein