CHE2: CHEMICAL BONDING

Noble gases have full outer most shell e.g. Argo.2:8:8, Neon 2:8. They is stable therefore don’t read with other elements. Element which  don’t  have  full  sets  of  element  in  the  outer  most  shells  are  unstable e.g. sodium (Na)2,8,1. These elements  attains  stable noble gas  structure  by  combing  with   others  elements  from  or molecules. There   are two main types   of bonding i.e.

• Ionic bonding  (electrovalent bonding)
• Covalent bonding

Ionic (electrovalent bonding)

An  ionic  blind  is  formed  by  transfer  of  one  or  more  electronic  from  the  most  shell  of  metal  atoms  to  the  outer  most  shell  of  non  metal  atoms  to  form  stable  ions  with  nobles  gas  structures  .

Note:

The  metal  atoms  (sodium) is  converted to  a  positive  cation, Na⁺.non  metal atoms  (chlorine) is  converted  in  negative  Anion  CL ^–

 

The  change  of  the  metal  ions  is  positive  and  the  size  of the  charge  is  the  same  as  the  numbers  of  electrons  removed. the  charge  of  the  non  metals  is  negative  and  its  size  is  the  same  as  the  number  of  electrons’  gained.

 

Consider formation of magnesium chloride, MgCl₂

The chloride atom requires only 1 electron to form stable noble gas structure. The magnesium atoms have 2 electrons in its outermost shell to donate. Therefore, one magnesium atoms transfers two electrons, each to one atom to form magnesium chloride.

Consider forming of calcium oxide, CaO

The calcium atoms donates 2 electrons to the oxygen atoms to form 1 calcium ion, Ca²⁺ and 0^2-

 

Properties of ionic compounds

1. They conduct electricity when molten(fused) in aqueous solution .this  is  because ionic  compounds consist  of  positively  charge  ions  which  are  free  to  move  in the  molten  form  or  in  aqueous  solutions and conduct  on  electric

 

Ionic compound are non-conductors of electricity in the solid form. This is because in  the  solid  the ions are immobile.

2. Usually they have high melting point. This is because a lot of heat energy required breaking the strong electrostatic forces holding the ions together in the regular lattice.

 

3. Usually ionic substances are  crystalline solids
4. Usually dissolved in polar solvent. E.g. water.
5. Usually they are insoluble in non – polar solvent.

Parts of the sodium chloride are crystal  Ag98

 

Covalent bonding

Covalent bonding is formed when a plain electrons is share between two atoms usually the involved are non-metallic

Covalent bonding results into formation of molecules.

Each  of  the  hydrogen  atoms  contributes  one  electron  for sharing to  one  covalent  bond

The pairs of electrons shared are called electron bond pair.

Valency line

Classic H – H single bonding

Formula

Each valence line represents one pair of share electrons.

The  numbers  of  atoms  in  a molecule of  element  is  termed  as  atomicity

Classical formula

Each chlorine atom requires one electron to form stable Nobolegas structure. The 2 atoms combine by sharing one electron pair to form a chlorine molecule.

In the formation of the oxygen molecule, 2 electrons combine by sharing 2 electrons pairs to form a double bond.

A double bond is stronger than a single bond and a triple bond is stronger than a double bond.

In the formation of Nitrogen molecule, two Nitrogen atoms combine 3 electron bond pairs to form a triple bond.

The triple bond formed is very strong and is not easy to break. This explains why Nitrogen is not very reactive.

Bonding in water

Classical formula

Lone pair

Pair of electrons in the outer most shell, which isn’t used 4 bonding.

FORMATION OF GAS METHAN & MOLECULE

4 electrons bond pairs. No lone pairs.

FORMATION OF MOLECLE OF CARBON TETRA CHLORIDE (TETRACHLOMETHAN)

Properties of covalent compounds

1. Usually gas or liquids e.g hydrogen, oxygen, water, paraffin.

 

1. Low melting and boiling points because of weak forces of attraction between molecules.

 

1. Non electrolytes, this is because, they consist of molecule, and not ions .

 

1. They dissolve in non-polar solvents (organic solvents) and usually insoluble in polar solvents.

Electrolyte

A substance that conducts electricity in molten or aqueous solution and is decomposed by the current e.g. table salt. (sodium chloride)

 

Non electrolyte –

A substance which doesn’t conduct electricity in molten form and aqueous solution.

METALLIC BONDING- bonding in metals

Pure metals are made up of atoms of the same kind. A metal consist of positively charged ions surrounded by a cloud of valency electrons which are free to move about within the solid.

The free / delocalized electrons attract the positively charged ions thus binding then together, equally and strongly .At the same time, positively charged ions attract delocalized electrons , preventing them from dispensing , resulting into a metallic bond .

The electrostatic attractions, bind the entire crystals a single unit. This is illustrated in figure.

The negative charge is representative of delocalized electrons and positively charge is the representative of positively nucleus.

Due to presence of delocalized of electricity and heat. Metal generally have high densities because the ions are classily parked in the lattice because of strong bonds between the ions , caused by free electrons the melting points of most metal are high.

 

STRUCTURES OF SUBSTANCES

There are different types of structures found in pure materials

1. Molecular structure

This contains separate gas of atoms called molecule. The atoms in a molecule are tightly held together by solvent bond s, but the forces between the molecules are very weak.

Molecule structure is divided into 2 gases.

1. Simple molecule structure

These consist of small molecule because of weak intermolecular forces of attraction carbondixide, hydrogen, chlorine, methane. A few solids e.g. Vaseline, shoe, more examples of solids are iodine, sulphur and phosphorous.

1. Giant molecule structure

These consist of large molecules and therefore they are solids with high melting points e.g. silicon dioxide.

In silicondixide, each silicon atom is bonded to 4 oxygen atoms and each oxygen atom is bonded to 2 silicon atoms.

Structure with molecule structures doesn’t conduct electricity because they don’t have free electrons or ions.

– They are usually insoluble in water but dissolve in non polar solvents.

-Substances with giant molecule structures have both high melting and boiling points.

GIANT ATOMIC STRUCTURES

In such structures; covalent bonding links the atoms into a network of atoms against structure of atoms.

Carbon has the ability to form a giant atomic structure e.g. Graphite and diamond.

GIANT ION STRUCTURES

These consist of many oppositely charged ions held 2gether by electrostatic attraction e.g. sodium chloride. In sodium chloride; each sodium ion has 6 equidistant chloride ions around it arranged, artachedrally. Also each chloride ion has 6 equidistant sodium ions around it. Also arranged actahedraliu as shown in figure 8.4 pg 48 Atkinson 4^th editions.

Structure with giant ionic structure have high melting point because a large amount of heat energy is need to break the structure due to the strong electrostatic forces between ions.

 

GIANT METHALLIC STRUCTURES

Metals consist of metallic structure accepts mercury which is a liquid. They have high melting points and electricity

CHEMICAL FOURMULAE

 

Valency or combining No

The valency or combing number is the measure of power of a nelentent or radical to combine with others.

Hgdrogen is the standard and it has the valency of /

Or

The valency of an element /radical is number of hydrogen atoms which combine with / displace one atom of an element. (One group of the radical)

Writing formulae

We use symbols, radical and valencies 2 write formulae of the compounds.

The rules are as follows. E.g

1. Write chemical formulae for following compounds.
2. Sodium sulphate – Na SO₄
3. Copper (ii)chloride –Cu Cl

 

Rules 1

Write the symbols for elements and radicals.

Rules 2

Write the valency below the symbols

Na₁                  SO4₂                CU₂                 CL₁

Rules 3

Write the symbols again reversing the valencies and writing the numbers (but not 1) below and to the right.

Na₁                  SO₄                       CU₂                 CL₁

₂

Na₂                  [SO₄]₁                  [CU] ₁              CL₁

_{2                                               2}

 

Therefore

Na₂SO₄                                                CUCL₂

 

Write chemical formulae for the following.

1. Sodium chloride

Na₁ CL₁

NaCL

 

2. copper (ii) oxide

Cu₂ O₂

CuO

 

3. copper (i) oxide

Cu₂     O₂

Cu₂    [O]₂                                  Cu₂ O

 

4. Iron (i) sulphate

Fe₂ So₄

                ₂                                              Fe So₄

 

Write chemical formulae of the following compounds.

• Lead (ii) oxide

Pb²       O²

PbO

 

• Manganese (vii) chloride

Mn⁷     CL¹

Mn[CL]₁

 

• Potassium chloride

 

• Magnesium sulphate

Mg2        SO⁴

Mg₂ [SO₄]₂

 

• Water

H₂O

Ammonia

NH₃

 Methane

CH₄

Sodium hydrogen sulphite

Na¹      HSO¹₃

NaHSO₃

Ntric acide

H¹      NO¹₃

HNO₃

 Hydrogen acid

HC1

sulphric  acid

H¹        SO²₄

H₂SO₄

Write the symbols of the following

1. An tom of chloride

CL

One molecule of chloride

CL2