chem bond final Flashcards
structure and bonding of an ionic compound
Ionic compounds in the solid state have a giant ionic lattice structure held together by *strong electrostatic forces of attraction** between oppositely charged ions in an ionic compound.
what comes together to form ionic bonds and how to tell which is the anion and cation
Electrons are transferred from metal atoms to non-metal atoms to form ions that come together in a solid ionic compound.
● The atom that transferred the electron(s) gets positive charge(s) and becomes a cation.
● The atom that gained the electron(s) get negative charge(s) and becomes an anion.
hence metals become cations and non-metals become anions
Sodium forms the oxide Na2O. Explain why the oxide of sodium has this formula.
Each Na atom has one valence electron. To attain noble gas electronic configuration, each Na atom loses its valence electron to form a 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. Therefore, the formula is Na2O.
physical properties of ionic compounds
▪ High melting and boiling points
▪ Soluble in water
▪ Conducts electricity in molten and aqueous state
▪ Hard, rigid and brittle
Why do ionic compounds have high melting and boiling points?
Ionic compounds have a giant ionic lattice. In melting, large amount of energy is supplied to overcome the strong electrostatic forces of attraction between the oppositely charged ions to break the giant ionic lattice to form free ions.
how is the strength of ionic bonding determined by the charge of the ions, and their radii.
The higher the charge and the smaller the radii of the ions(ionic radii), the stronger the ionic bonding.
Between NaCl and MgO, which compound would be expected to have the higher melting point? Explain.
▪ Both NaCl and MgO have a giant ionic lattice.
▪ However, Mg2+ and O2─ have higher charge and smaller ionic radius than Na+ and Cl- (higher charge means more electromagnetic attraction = closer to nucleus)
▪ Hence the strength of the ionic bonds in MgO is larger than that of NaCl.
▪ More energy is needed to overcome the stronger electrostatic forces of attraction between the oppositely charged ions in MgO.
▪ MgO will have a higher melting point.
What happens when an ionic salt dissolves in water?
When an ionic salt dissolves, each ion on the crystal’s surface attracts the oppositely charged poles of the polar water(solvent) molecules and the ions become hydrated (or solvated if solvent is another polar solvent). This hydration process releases energy. The ionic crystal structure breaks down and the solid dissolves.
Why is it that ionic compounds do not conduct electricity in the solid state but conducts in the molten and in aqueous solutions?
Ionic compounds do not conduct electricity in the solid state as the ions are fixed in positions and are not free to move. In molten and in aqueous solutions, the ions are mobile. The ions are **free to move and flow towards the oppositely charged electrodes and act as mobile charge carriers, carrying a current.
Why are ionic solids Hard, rigid and yet brittle
In an ionic lattice, oppositely charged ions are held in fixed positions throughout the crystal lattice by strong ionic bonding. Moving the ions out of position requires large amounts of energy to break these bonds. Ionic lattices are therefore quite hard and rigid.
However, if enough pressure (e.g. by cutting or knocking) is applied, ions of like charge are brought next to each other. Repulsion between ions of like charges will cause the lattice to shatter apart. Ionic lattices are therefore said to be brittle.
structure and bonding of a metallic compound
Metals in the solid state have a giant metallic lattice structure, held together by metallic bonding. Metallic bonding is the electrostatic force of attraction between a lattice of metal cations and the sea of delocalised electrons in the metallic lattice.
what affects Strength of metallic bond s
Number of delocalised valence electrons in the structure.
–>The larger the number of valence electrons contributed per atom, the greater the number of delocalised electrons and the stronger the metallic bonding.
Charge and radius of the metal cation.
–>The higher the charge and the smaller the radius of the metal cation, the greater electrostatic force of attraction between the cations and the sea of delocalised electrons.
Physical properties of metals
▪ High melting and boiling points
▪ Conducts electricity
▪ Good conductor of heat
▪ Malleable and ductile
▪ Shiny surface
▪ Hard
y doe metals have a High melting and boiling points
_Most metals are solids with moderately high melting points and much higher boiling points. Metals have a giant metallic lattice structure which consists of a lattice of metal cations with a sea of delocalised electrons and the electrostatic forces of attraction between the cations and the delocalised electrons constitute the metallic bond. _
metallic bonding spam
Melting and boiling points of metals are relatively high because a large amount of energy is required to overcome the relatively strong electrostatic forces of attraction between the cations and delocalised
electrons.
Why are metals good electrical conductors?
Metals are good electrical conductors because the delocalised electrons which act as mobile charge carriers are free to move about in the solid structure.
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.
