Chapter 4 Flashcards
What is an ion
An ion is a charged particle. Ions form from neutral atoms or from groups of atoms by loss or gain of one or more valence electrons
Atoms gain or lose electrons in order to achieve a more stable electron arrangement
Generic formation of ion trend in the periodic table
Atoms in groups 1,2 and 13 lose their electrons and become cations
Atoms in groups 15,16 and 17 gain electrons to become anions
Atoms in group 14 generally do not form ions
Exceptions to the ion trend
Lead (Group 14) forms Pb+2
Tin (Group 14) forms Sn+4 and Sn+2
Hydrogen can form H- (hydride ion) as well as H+ (hydrogen ion)
Transition metals have variable oxidation states, however silver tends to form Ag+
Ionic compounds
Ionization occurs when electros are transferred between atoms (typically from a metal to a non-metal)
The oppositely charged resultant ions are attracted to each other and held together by electrostatic forces (an ionic bond) to form an ionic compound
Ionic formulae
Ionic compounds are electrically neutral. Therefore, the charges of the positive and negative ions that make up the compound must be balanced in the lowest common ratio
Describe lattice structure
In the solid state. ionic compounds take on a crystalline lattice structure
The geometry of this lattice varies by the compound, however, we can use the coordination number to describe the number of ions that surround a given ion in the lattice
Lattice energy is a measure of strength of attraction of ions within the lattice
Describe lattice structure
In the solid state. ionic compounds take on a crystalline lattice structure
The geometry of this lattice varies by the compound, however, we can use the coordination number to describe the number of ions that surround a given ion in the lattice
Lattice energy is a measure of strength of attraction of ions within the lattice
Factors which lattice energy depends upon
Magnitude of the charge
- 2+/- ions have a higher lattice energy than 1+/- ions
Distance between the ions - the size of the ion
- smaller ions pack together tighter and so have a stronger bond
Describe the structure of ionic compounds
A lattice structure consisting of cations and anions held together by electrostatic force of attraction
Melting and boiling point of ionic compounds
Strong electrostatic between ions in the ionic lattice require large amounts of energy to break resulting in high melting and boiling points
Typically solid at room temperature
Melting and boiling points increase with oxidation number
What is volatility?
The tendency of a substance to vaporize
Solubility of ions
solubility refers to the ease with which a solid becomes dispersed through a liquid to form a solution
Ionic compounds are generally soluble in ionic or polar solvents but not soluble in non-polar solvents. Generally solubility is determined by the degree to which separated solute particles are able to form bonds with the solvent
Conductivity of ions
Conductivity indicated the ability compound to conduct electricity based on whether it contains ions that are able to move and carry a charge
Brittleness of ions
When a force is applied, repulsive forces cause the lattice to shatter, and hence ionic compounds are brittle
Different between ionic and covalent compounds
Ionic:
Reactive metal + reactive non-metal
electronegativity difference > 1.8
Covalent:
two non-metals
electronegative difference < 1.8
What is metallic bonding?
The electrostatic force of attraction between a lattice of positive ions and delocalized electrons
What factors affect the strength of metallic bonds
The number of delocalized electrons
The charge of the cation
The radius of the cation
Conductivity of metals
Presence of mobile electrons cause electrical conductivity of a metal
When a potential difference is applied across the metal sheet, the free mobile electrons in the metallic crystal start moving towards the positive electrode
The electrons coming from the negative electrode simultaneously replace these electrons
Thus, the metallic sheet maintains the flow of electrons from negative electrode to positive electrode. This constitutes electrical conductivity
Ductility of metals
Metals can be beaten into sheets (malleability) and drawn into wires (ductility). Metallic bonds are non-directional in nature
The electrons “insulate” the cations from one another, hence the cations can slide past one another when a pressure/force is applied to the metal
What are alloys
solid solutions usually containing more than one metal. held together by metallic bonding
Properties of alloy s are distinct from their component elements due to the packing of the cation in the lattice; alloys are often more chemically stable, stronger and more resistant to corrosion
What is a covalent bond
the electrostatic attraction between a pair of shared electrons and positively charged nuclei
A group of atoms held together by covalent bonds form a molecule. Atoms can share 1,2 or 3 pairs of electrons in order to achieve a more stable electron configuration
What is bond length
Covalent bond characterized by two values; bond length and bond strength
Bond length at which a covalent bond forms minimizes the energy of the system
What is bond strength
Provides a measure of the energy required to break a bond
Short bonds are strong bonds, and hence we can use atomic radius to gauge the relative strength of different bonds
