s2.1 ionic model Flashcards
define ionic bonding
electrostatic attraction between oppositely charged ions. metals lose electrons and the electrons are transferred to non-metals
define covalent bonding
electrostatic attraction between a shared pair of electrons and the positively charged nuclei
define metallic bonding
electrostatic attraction between a lattice of positive ions and delocalised electrons
what is an ion?
an ion is an electrically charged species that is formed after an atom gains or loses electrons. they obtain the same electron configuration as the stable noble gases
define isoelectronic
sharing the same electron configuration
what are cations?
cations (positive ions) form when electrons are lost. the energy associated with this is known as ionisation energy
what are anions?
anions (negative ions) form when electrons are gained. the energy associated with this is known as electron affinity
what are transition metal ions?
transition elements can form more than one positive ion. this is because they lose their electrons from the 4s subshell first
how do you name binary ionic compounds?
the cation is listed first (same as the neutral element)
the anion is listed second (suffix changes to -ide)
what is a polyatomic ion?
a group of covalently bonded ions
list all the polyatomic ions
ammonium - NH₄⁺
hydroxide - OH⁻
nitrate - NO₃⁻
hydrogen carbonate - HCO₃⁻
carbonate - CO₃²⁻
sulphate - SO₄²⁻
phosphate - PO₄³⁻
what is electronegativity?
electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond. electronegativity values can also be used to determine whether an ionic compound will result from two specific elements reacting together. it is generally recognised that a difference of 1.8 units or more on the pauling scale will give a compound that is predominantly ionic
what is the structure of ionic compounds?
the structure of ionic compounds is a giant ionic lattice. each ion is surrounded by oppositely charged ions. these ions attract each other from all directions (meaning it is non-directional)
what is lattice enthalpy?
lattice enthalpy (ΔHθₗₑ) is the enthalpy change when 1 mole of an ionic lattice is broken down into it’s gaseous ions under standard conditions (273.15K and 100kPa)
the enthalpy change is positive, so ionic lattice breakdown is endothermic
what do lattice enthalpy values mean?
lattice enthalpy values indicate the relative strength of ionic bonds (more endothermic lattice enthalpy values means stronger ionic bonds)
how does ionic size impact lattice enthalpy?
ΔHθₗₑ decreases with increasing ionic radius. as the ionic size increases, there is weaker electrostatic attraction between the ions, so the lattice enthalpy will be less endothermic
how does ionic charge impact lattice enthalpy?
ΔHθₗₑ increases with increasing ionic charge. increased ionic charge will result in a stronger electrostatic attraction. this will result in a more endothermic lattice enthalpy and a higher melting point
why do ionic compounds have a high melting point?
ionic compounds have high melting and boiling points due to having strong ionic bonding so ionic compounds are solid at room temperature. a larger ionic charge or a smaller ionic radii produces stronger ionic bonds, which results in a higher melting point
why are ionic compounds brittle?
ionic compounds are brittle as when a force is applied, the layers of the lattice move and similar charged ions will be next to each other, causing a repulsion split
do ionic compounds conduct electricity?
ionic compounds do not conduct electricity when solid as the ions are not mobile. however, ionic compounds do conduct when molten or in aqueous solution as the ions become mobile and conduction takes place
why are ionic compounds soluble?
solvents like water are called polar solvents because they have partial charges so ionic compounds can dissolve in them. non polar solvents (e.g. hexane) do not have partial charges and therefore cannot dissolve ionic compounds
when an ionic compound is added to water, the water molecules position themselves so that their partial charges attract the oppositely charged ions in the compound
ionic compounds are insoluble in water when the electrostatic attraction between the cation and the anion is stronger than between the ion and the water
