Chemistry Topic 4.1 Ionic bonding and structure
FORMULA: HYDROXIDE
OH⁻
WHERE ARE ELEMENTS WITH A LARGE DIFFERENCE IN ELECTRONEGATIVITY FOUND?
Opposite sides of the periodic table
FORMULA OF OXIDE ION
O²⁻
FORMULA: PHOSPHATE
PO₄³⁻
FORMULA OF LEAD
Pb²⁺
POLAR SUBSTANCES ARE SOLUBLE IN...
Polar solvents
CATIONS
Positively charged ions
FORMULA OF PHOSPHIDE ION
P³⁻
IONIC BONDS FORM BETWEEN ELEMENTS THAT HAVE...
A large difference in electronegativity (typically greater than 1.8)
FORMULA OF ALUMINIUM ION
Al³⁺
IONIC COMPOUNDS
Are composed of a metal and non-metal element Eg. sodium and chloride
HYDRATION
At the surface of the ionic lattice, where it is in contact with the water, the (+) and (-) dipoles of the water molecule are attracted to the oppositely charged ions in the lattice structure. These ions break off from the lattice and are surrounded by water molecules. Process = hydration
POLARITY OF WATER AND SOLUBILITY OF IONIC COMPOUNDS
At the surface of the ionic lattice, where it is in contact with the water, the (+) and (-) dipoles of the water molecule are attracted to the oppositely charged ions in the lattice structure. These ions break off from the lattice and are surrounded by water molecules. This process is known as HYDRATION. When this happens, the solid dissolves.
HOW DO ATOMS BECOME ANIONS
Atoms can gain electrons, which means they have more electrons than protons, giving them an overall negative charge
FORMULA: CARBONATE
CO₃²⁻
ELECTRICAL CONDUCTIVITY OF IONIC COMPOUNDS
Can't conduct electricity when solid as ions are in fixed positions in lattice structure But when an ionic compound is molten (melted) or dissolved, the ions are free to move and carry an electric current
FORMULA OF CALCIUM ION
Ca²⁺
FORMULA: CHLORATE
ClO₃⁻
WHAT DOES MELTING POINT OF AN IONIC COMPOUND DEPEND ON?
Depends on the ionic charge and the ionic radius of its component ions The greater the charge on ion and the smaller its ionic radius, the greater the attraction between the oppositely charged ions. Therefore, the higher the melting point
VOLATILITY
Describes how easily a substance evaporates/ tendency of a substance to vaporise
WHAT PHYSICAL STATE DO IONIC COMPOUNDS HAVE UNDER STANDARD CONDITIONS AND WHY
Due to high boiling and melting point, they are solid under standard conditions
NEUTRAL ATOMS HAVE...
Equal numbers of protons and electrons
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS
Generally highly soluble in water. Show good electrical conductivity when molten or dissolved. Solid at RT. High m.p's and b.p's Brittle
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS: EXPLANATION: SOLUBILITY IN WATER
Generally highly soluble in water: Water molecules are attracted to the oppositely charged ions causing them to dissolve (depends if forces of attraction are strong enough)
FORMULA: HYDROGEN CARBONATE
HCO₃⁻
STRUCTURE OF IONIC COMPOUNDS
Have a lattice structure in which ions are held in fixed positions
WHICH OF THE FOLLOWING STATEMENTS BEST DESCRIBE THE STRUCTURE OF THE SODIUM CHLORIDE, NaCL, LATTICE? I. EACH SODIUM ION IS SURROUNDED BY SIX CHLORIDE IONS. II. THE OPPOSITELY CHARGED IONS ARE HELD TOGETHER BY ELECTROSTATIC FORCES OF ATTRACTION. III. THE LATTICE FORMS A CUBIC STRUCTURE.
I II and III
WHAT IS THE CRITERIA OF AN ELEMENT IN ORDER FOR AN IONIC BOND TO FORM?
In order for an ionic bond to form between two elements, elements with an electronegativity difference of approximately 1.8 units and greater
IONIC BONDING
Involves the transfer of one or more electrons from the outer shell of one atom to the outer shell of another atom The transfer of these electrons results in the formation of positive and negative ions
WHAT TYPE OF BONDING OCCURS BETWEEN A POLYATOMIC ION AND ANOTHER ION
Ionic bonding (Even though bonds in polyatomic atoms are covalent)
WHAT IS THE CRITERIA OF AN ELEMENT IN ORDER FOR AN IONIC BOND TO FORM?
Ionic bonds are formed by elements with an electronegativity difference of approximately 1.8 units and greater
WRITING THE FORMULAE OF IONIC COMPOUNDS: CHARGES
Ionic compounds are electrically neutral. Therefore, when writing the formula for an ionic compound, the charges on the oppositely charged ions must cancel out to leave the compound with no overall charge
MELTING AND BOILING POINT OF IONIC COMPOUNDS
Ionic compounds are held together by the electrostatic attractions between the oppositely charged ions. The strong attraction between the ions results in ionic compounds having relatively high melting and boiling points. This means that relatively large amounts of energy are required to break these forces of attraction between the ions.
4.1 ESSENTIAL IDEA
Ionic compounds consist of ions held together in a lattice structure by ionic bonds
BRITTLENESS OF IONIC COMPOUNDS
Ionic compounds tend to shatter when a force is applied; they are said to be brittle. They fracture across a plane when the layers of ions become incorrectly aligned
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS: EXPLANATION: HIGH MP'S AND BP'S
Ions are attracted to each other by strong electrostatic attractions. Large amounts of energy are needed to separate them.
POLYATOMIC IONS
Ions that consist of more than one atom The atoms that make up the polyatomic ion are bonded by covalent bonds
WHICH OF THE FOLLOWING IONIC COMPOUNDS WOULD YOU EXPECT TO HAVE THE HIGHEST MELTING POINT? LiF KF RbF NaF
LiF (smallest ionic radius)
SOLUBILITY OF IONIC COMPOUNDS
Many (but not all) dissolve in water Property depends on whether the forces of attraction between the water molecules and the ions in the lattice structure are strong enough to overcome the attractions between the ions themselves
WHICH MOLECULES EXHIBITS ONLY IONIC BONDING: NH4Cl NaNO3 MgBr2 H2SO4
MgBr₂
FORMULA OF MAGNESIUM ION
Mg²⁺
FORMULA: AMMONIUM
NH₄⁻
FORMULA: NITRITE
NO₂⁻
FORMULA: NITRATE
NO₃⁻
IONIC COMPOUNDS: SODIUM AND CHLORIDE
Na electron configuration: 1s² 2s² 2p⁶ 3s¹ Due to low ionisation energy, Na loses its 1 valence electron to form 1+ ion (Na⁺) (cation) Cl electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁵ By gainin 1 electron, it achieves an electron configuration of a noble gas (Cl⁻) (anion) The oppositely charged ions are attracted to one another, resulting in the formation of an ionic bond
HYDRATION + SOLID DISSOLVING OF NACL EQUATION
NaCl (s) → Na⁺ (aq) + Cl⁻ (aq)
ANIONS
Negatively charged ion
WHAT IS THE KEY TO THE FORMULA OF SODIUM CHLORIDE
No matter how big the crystal is, the ratio of Na⁺ : Cl⁻ is always 1:1
WHAT IS IONIC BONDING DESCRIBED AS BEING...
Non-directional as the force of attraction occurs in all directions around the individual ions
SOLUBILITY: WHAT CANNOT DISRUPT THE LATTICE STRUCTURE OF IONIC COMPOUNDS IN THE SAME WAY?
Non-polar solvents cannot disrupt the lattice structure in the same way, therefore the solubility of ionic substances in solvents such as hexane and propanone is limited.
WHAT IS SOLUBLE IN NON-POLAR SOLVENTS
Non-polar substances
FORMULA OF NITRIDE ION
N³⁻
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS: EXPLANATION: BRITTLE
Repulsion between ions of the same charge causes the lattice structure to split and fracture.
FORMULA: SULPHITE
SO₃²⁻
FORMULA: SULPHATE
SO₄²⁻
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS: EXPLANATION: ELECTRICAL CONDUCTIVITY
Show good electrical conductivity when molten or dissolved: As ions are free to move
OCTET RULE
States that atoms are more stable with the electron configuration of a noble gas reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas
FORMULA OF SULPHIDE ION
S²⁻
COORDINATION NUMBER OF NACL
The Na ion in the centre is in contact with 6 chloride ions so the coordination number of the sodium is 6 Alternatively if Cl was in the centre then the Cl would be in contact with 6 other Na ions and therefore have a coordination number of 6 Therefore, sodium chloride is described as being 6:6 coordinated
WHAT IS AN IONIC BOND?
The electrostatic attraction between the positive and negative ions
WHAT IS IN ACCORDANCE WITH THE OCTET RULE?
The formation of positive and negative ions resulting in atoms achieving a full outer shell of electrons
FIELD OF IONIC CRYSTALS DEMONSTRATES
The impressive beauty of self-assembly and order
OVERVIEW OF GENERAL PROPERTIES OF IONIC SOLIDS: EXPLANATION: SOLID AT RT.
The ions are held in fixed positions by strong electrostatic attractions in the lattice structure Due to high bp and mp
WHAT DOES ELECTRICAL CONDUCTIVITY OF A SUBSTANCE DEPEND ON?
The presence of mobile ions
COORDINATION NUMBER
The total number of points of attachment to the central element
POLARITY OF WATER MOLECULES
They are polar due to the difference in electronegativity between oxygen and hydrogen
WHEN AND WHY DO IONIC COMPOUNDS FRACTURE/ BREAK
They fracture across a plane when the layers of ions become incorrectly aligned This occurs because the movement of the ions within the lattice when the force is applied places ions of the same charge next to each other. The forces of repulsion between ions of the same charge cause the lattice structure to split and fracture.
VOLATILITY OF IONIC COMPOUNDS
They have low volatility because of the strong forces of attraction between the ions in the lattice structure
IONIC SUBSTANCES FRACTURE...
Under stress (force being applied)
HOW DO ATOMS BECOME CATIONS
When atoms lose electrons, they have more protons than electrons and therefore become positively charged
ELEMENT X IS IN GROUP 13 AND ELEMENT Y IS A HALOGEN FROM GROUP 17 OF THE PERIODIC TABLE. WHICH IS THE MOST LIKELY FORMULA OF THE COMPOUND FORMED WHEN X AND Y REACT TOGETHER?
XY₃
WHICH OF THE FOLLOWING IS THE MOST LIKELY FORMULA OF THE COMPOUND FORMED WHEN ELEMENT X (IN GROUP 13) AND ELEMENT Y (FROM GROUP 16) REACT TOGETHER?
X₂Y₃
FORMULA OF ZINC
Zn²⁺