Chemical bonding Flashcards
Sodium forms the oxide Na2O. Explain why it has this formula
Each Na atom has one valence electron. To attain noble gas electronic configuration, each Na atom loses one valence electron to form Na+ cation.
Each O atom has six valence electrons. To attain noble gas electronic configuration, each O atom gains two electrons from two Na atoms to form an O2- anion.
In the resultant giant ionic lattice formed, the ratio of Na+:O2- is 2:1 such that the lattice is electrically neutral overall.
Why do ionic compounds have high melting and boiling points?
Ionic compounds have a giant ionic lattice structure. In melting, a large amount of energy is required to overcome the electrostatic force of attraction between the oppositely charged ions to break the giant ionic lattice to form free ions.
What happens when ionic salt dissolves?
Each ion on the crystal’s surface attracts the oppositely charged poles of the polar water molecules and the ions become hydrated. This hydration process releases energy. The ionic crystal structure breaks down and the solid dissolves.
Why ionic compounds do not conduct electricity in solid state?
The ions are fixed in position and not free to move. In aqueous solutions, the ions are mobile. They are free to move and flow towards oppositely charged electrodes and act as mobile charge carriers, carrying a current.
Why are ionic solids hard, rigid and brittle?
Ions of liked charge will be brought next to each other. Repulsion between ions of like charges will cause the lattice to shatter apart.
Metallic bonding
The electrostatic force of attraction between a lattice of metal cations and the sea of delocalised electrons
Strength of the metallic bond is determined by?
Number of delocalised electrons: larger the number of valence electrons contributed per atom, greater the number of delocalised electrons and stronger the metallic bonding.
Charge and radius: Higher the charge and smaller the radius, the greater electrostatic force of attraction between the cations and the sea of delocalised electrons.
Describe the structure and bonding in calcium
The structure of calcium metal is a giant metallic lattice containing an array of Ca2+ ions, with the valence electrons of calcium removed and free to move throughout the lattice. Metallic bonding exists between the resultant Ca2+ cations and the sea of delocalised valence electrons.
Note for drawing metallic bonding
Cations should be in a regular arrangement, electrons are present between cations
Why are metals good electrical conductors?
The delocalised electrons act as mobile charge carriers and are free to move about. When a piece of metal is attached to a battery, electrons flow from the negative terminal into the metal and replace electrons flowing from the metal into the positive terminal.
Why are metals good heat conductors?
They have mobile delocalised electrons. The electrons disperse heat quickly from a region with higher temperature to a region of lower temperature. The more energetic electrons collide with and speed up the slower, less energetic electrons, thereby allowing for good heat conducting.
Reasons for ductility and malleability
In a giant metallic lattice structure, metal ions are held in an orderly array. When an external force is applied, the layers of metal ions slides past each other and move into new positions. The overall shape changes but the metal does not break because the sea of delocalised electrons prevents repulsion among the cations as they move past each other. Metallic strength stays the same and metallic bonding is termed non-directional bonding.
Bronze
Copper (90%)
Tin （10%）
Hard and Strong
Brass
Copper (70%)
Zinc (30%)
Corrosion resistant
Steel
Iron (99.8%)
Carbon(0.2%)
Hard and strong
