Test 2 Flashcards
Atomic Radius across a period
As we move across a period, there is an increase in protons, neutrons and electrons. However, the number of inner shell electrons (shielding effect) remains constant, whilst the number of protons in the nucleus (effective nuclear charge) increases. This means the electrons experience a stronger electrostatic force pulling them into the nucleus. As a result the average distance between the nucleus and the most loosely bound electron, reducing atomic radius.
Atomic Radius down a group
Going downa group, there is an increase in prinipal energy levels. Thus the outermost electron is further from the nucleus. Despite the increase in protons, there is also an increase in shielding electrons, meaning the effective nuclear charge remains constant. Hence the atomic radius increases.
First Ionisation Energy down a group
As we go down a group, there is an increase in additional principal energy levels. As a result, the most loosely bound electron is further from the nucleus, and will not be attracted as strongly to the nucleus. Thus, less energy will be required to remove the outermost electron from a larger atom. Thus the ionisation energy decreases.
First Ionisation energy across a group
As we move along a period, the core charge increases, as a result, it will be more difficult to remove an electron from the atoms with larger core charges in a particular period, thus there is an increase in first ionisation energy.
Electronegativity down a group
As we move down a group, the atomic radius increases, thus there is a greater distance between the nucleus and an incoming electron, and so an incoming electron is not attracted as strongly. Thus the electronegativity decreases.
Electronegativity across a period
As we move across a period, the atomic radius decreases, thus there is a lesser distance between the nucleus and incoming electron, the core charge increases, thus an incoming electron is not attracted more strongly. Thus the electronegativity increases.
Electronegativity
Ability of an electron to attract a bonding pair of electrons
Ionisation Energy
Energy required to remove 1 mol of electrons from 1 mol of atoms in the gaseous state to produce 1 mol of ions
Metallic Properties
Good reducing agents and reactive - it is easy for them to lose electrons due to low ionisation energies.
Non-metal properties
Form covalent bonds
Tend to be reduced - due to high ionisation energy and high electronegativity
Reactivity decreases down groups - decreasing reactivity
Metals are good conductors of electricity
To be able to conduct electricity, a substance must have mobile charged particles. The sea of electrons are able to carry these charges and spread them over the metal, hence metals are good conductors of electricity.
Metals are good conductors of heat
To conduct heat, a substance must have mobile charged particles. The sea of electrons in a metal lattice are able to carry heat energy as kinetic energy and spread it throughout the metal lattice. The vibration of metallic ions also contributes to the flow of heat through the metal lattice.
Metals are malleable and ductile
Bonding between metal ions and the sea of electrons is non-directional. If sufficient force is applied, it can cause individual atoms in the lattice shift. However, due to the non directional bonding individual metal atoms can move in relations to each other without breaking the bonds between them and the sea of electrons. This allows a metal to change shape, without breaking.
Metals are solid at room temperature
Strong attractive forces between the metal ions and sea of electrons hold the metallic lattice together. As a consequence, a moderate to high temperature is need to disrupt the lattice and allow the metal to melt.
Ionic substances are poor conductors of electricity as solids
In an ionic solid the ions are tightly held in fixed positions within the lattice, thus they are unable to move and carry charge. Electrons within the ionic lattice are also tighely held by individual ions and hence also unable to move and carry through the ionic solid. An absence of mobile charged particles means ionic solids are non-conductors of electricity
Ionic liquids are good conductors of electricity
In the molten phase, ions are mobile and free to move and carry charge throughout the ionic liquid. Both positive and negative ions carry charge. Positive ions move towards the negative electrode while negative ions move towards the positive electrode
Ionic substances are good conductors of electricity when in aqueous solution
In an aqueous solution individual ions from the ionic solid are mobile and free to move independently of one another. Their mobility and charge enable them to conduct and electric current through the ionic solution. Both positive and negative ions are involved in conducting the current. The current consists for positive ions moving toward the negative electrode and negative ions moving toward the positive electrode.
Ionic substances are hard and brittle
If sufficient force is applied to the ionic lattice, it will cause layers of ions to move. When this happens, like charged ions will be forced to align alongside one another. This means like charges will be closer together than, unlike charges. Consequently, repulsive forces will exceed attractive forces and the lattice will break apart rather than dent or bend.
Ionic substances have high melting and boiling points
Ionic bonds are strong electrostatic attractive forces between ions. These strong attractive forces extend throughout the ionic lattice keeping individual ions in fixed positions. thus a high temperature, high particle kinetic energy, is needed to disrupt (melt) the ionic lattice.
Covalent molecular substances are non-conductors of electricity
The electrons in a covalent molecular substance are localised within each atom’s electron cloud or as shared electrons within covalent bonds. None of these electrons are free to move independently. Also these substances do not contain ions. the absence of any freely mobile charged particles explains why covalent molecular substances are non-conductors of electricity.
Some covalent molecular substances are good conductors of electricity in aquieuous solution
Covalent molecular substances which are acidic of basic react with water producing free mobile ions. The resulting ions are able to move freely throughout the solution carrying change and hence conducting an electric current
Soft and weak
Strong covalent bonds only form between the atoms within molecules. Only weak intermolecular forces of attraction occur between neighbouring molecules. Consequently molecules are easily separated from one other and hence these substances are weak and soft
Low to moderate melting and boiling points
When a molecular substance melts or boils, only weak intermolecular forces need to be broken or overcome. Thus the weakly bonded lattice of molecules in the solid phase is easily disrupted by heat energy to form a liquid or gas. The strong covalent bonds between atoms within the molecule are unaffected when a substance melts or boils.
Covalent Network Substances are non-conductors of heat and electricity
Electrons in these substances are held in fixed positions within the atom’s shells, lone pairs or covalent bonds. As the electrons are not free to move independently they are unable to conduct electricity or heat through the substance.
Very hard and brittle
Strong covalent bonds occur between all atoms withing a covalent network structure. this continuous array of strongly bonded atoms is difficult to disrupt and os these substances are characteristically hard and brittle.
