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 .
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 02-
Properties of ionic compounds
- 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.
- 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.
- Usually ionic substances are crystalline solids
- Usually dissolved in polar solvent. E.g. water.
- Usually they are insoluble in non – polar solvent.
Parts of the sodium chloride are crystal Ag98
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.
Classic H – H single bonding
Each valence line represents one pair of share electrons.
The numbers of atoms in a molecule of element is termed as atomicity
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
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
- Usually gas or liquids e.g hydrogen, oxygen, water, paraffin.
- Low melting and boiling points because of weak forces of attraction between molecules.
- Non electrolytes, this is because, they consist of molecule, and not ions .
- They dissolve in non-polar solvents (organic solvents) and usually insoluble in polar solvents.
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
- 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.
- 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.
- 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 4th 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
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 /
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)
We use symbols, radical and valencies 2 write formulae of the compounds.
The rules are as follows. E.g
- Write chemical formulae for following compounds.
- Sodium sulphate – Na SO4
- Copper (ii)chloride –Cu Cl
Write the symbols for elements and radicals.
Write the valency below the symbols
Na1 SO42 CU2 CL1
Write the symbols again reversing the valencies and writing the numbers (but not 1) below and to the right.
Na1 SO4 CU2 CL1
Na2 [SO4]1 [CU] 1 CL1
Write chemical formulae for the following.
- Sodium chloride
- copper (ii) oxide
- copper (i) oxide
Cu2 [O]2 Cu2 O
- Iron (i) sulphate
2 Fe So4
Write chemical formulae of the following compounds.
- Lead (ii) oxide
- Manganese (vii) chloride
- Potassium chloride
- Magnesium sulphate
Sodium hydrogen sulphite
Write the symbols of the following
- An tom of chloride
One molecule of chloride