Periodicity Flashcards
What is periodicity?
The repeating patters in the physical and chemical properties of the elements across the periodic table.
How can atomic radius be determined using different methods?
The distance between the two nuclei of the same type of atom can be determined and then divided by two to arrive at the atomic (single covalent) radius. There are other measures of atomic radii, such as metallic radii and van der Waals’ radii.
Why do atoms of noble gases in Group 18, such as argon in Period 3, do not have a covalent radius?
As they do not form bonds with each other.
How can the atomic radii of elements in Period 18 can be determined?
Through their van der Waal’s radius.
How to find an element’s van der Waal’s radius?
This is found by measuring the distance between the nuclei of two neighboring touching atoms, which are not chemically bonded together. The distance is then divided by two.
Why will the value of the van der Waal’s radius will be higher than the single covalent radius of finding given element?
Because there is no overlap of electron cloud’s in van der Waal’s radius.
Why does the size of atomic radius decrease across the period?
Across a period, the number of protons (and hence the nuclear charge), and the number of electrons, increases by one with each successive element. The extra electron added to the atoms of each successive element occupies the same principal quantum shell (energy level). This means that the shielding effect remains roughly constant. So the greater attractive force exerted by the increasing positive nuclear charge on the outer (valence) shell electrons pulls them in closer to the nucleus.
Why are cations smaller than when they were atoms?
The positively charged ions have effectively lost their outer shell of electrons (the third principal quantum shell or energy level) from their original atoms. Hence the cations are much smaller than their atoms. To add to this effect, there is also less shielding of the outer electrons in these cations compared with their original atoms.
Why are anions larger than their original atoms?
The negatively charged ions are larger than their original atoms. This is because each atom will have gained one or more extra electrons into their third principal quantum shell, increasing the repulsion between its electrons, whereas the nuclear charge remains constant. This increases the size of any anion compared with its atom.
What is the pattern of ionic radii across period 3 and how can one explain it?
cations compared with their original atoms.
Going across the period, from Na+ to Si4+, the ions get smaller for reasons similar to those for the decreasing
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Figure 10.5 Plotting the ionic radii against atomic number for the elements in Period 3 (argon not included).
atomic radii across a period. The increasing nuclear charge attracts the outermost (valence-shell) electrons in the second principal quantum shell (energy level) closer to the nucleus with increasing atomic number. The anions decrease in size, going from P3+ to Cl- the nuclear charge increases across the period.
What physical properties show trends across a period?
Atomic radius, Ionic radius, melting point and electrical conductivity.
How can we describe the pattern of the size of ionic radii down group 3 with an explanation of why such a pattern occurs?
Going across the period, from Na+ to Si4+, the ions get smaller for reasons similar to those for the decreasing atomic radii across a period. The increasing nuclear charge attracts the outermost (valence-shell) electrons in the second principal quantum shell (energy level) closer to the nucleus with increasing atomic number. The anions decrease in size, going from P3- to Cl- the nuclear charge increases across the period.
What happens to electrical conductivity of group 3 elements across a period?
The electrical conductivity increases across the metals of Period 3 from sodium (Group 1) to aluminium
(Group 13). The electrical conductivity then drops dramatically to silicon, which is described as a semiconductor, and falls even further to the non-metallic insulators phosphorus and sulfur.
What happens when an ionic solid dissolves in water?
When an ionic solid dissolves in water, the crystal lattice breaks up and the ions separate.
Ionic solid requires a large amount of energy to overcome the attractive forces between the ions. How does this happen when it’s dissolved in water, even when the water is not heated?
What is the standard enthalpy change of solution? (ΔH(symbol for standard conditions)sol)
the energy absorbed or released when 1 mole of an ionic solid dissolves in sufficient water to form a very dilute solution under standard conditions.
The enthalpy changes of solution for magnesium chloride is described by the equations:
MgCl2(s)+aq—>MgCl2(aq) ΔH(superscript: symbol for standard conditions; subscript: sol)=-55 kJ mol-1
Or MgCl2(s)+Mg2+(aq)+ 2Cl-(aq) ΔH(superscript: symbol for standard conditions; subscript: sol)=-55 kJ mol-1
Enthalpy changes of solutions can be
positive (endothermic) or negative (exothermic)
a compound is likely to be soluble in water only if
Standard enthalpy change of solution is negative or has a small positive value.
‘Soluble’ and ‘insoluble’ are only relative terms. Elaborate on this.
Magnesium carbonate is regarded as being insoluble because only 0.6 g of the salt dissolves in every dm3 of water. No metallic salts are absolutely insoluble in water. Even lead carbonate, which is regarded as insoluble, dissolves to a very small extent: 0.000 17 g dissolves in every dm3 of water. If salts were completely insoluble they could not have a value for standard enthalpy change of solution.
What is standard enthalpy change of hydration?
Is the enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form a very dilute solution under standard conditions.
The lattice energy for sodium chloride is –788 kJ mol .
This means that______
to overcome the forces of attraction between the ions.
we need to supply (at least) +788 kJ mol–1 of energy
The standard enthalpy change of solution of NaCl is only +3.9 kJ mol-1. Where does the remaining energy needed to separate the ions come from?
It comes from the strong attraction between the ions and the water molecules.
What happens when an ionic solid dissolves in water?
Bonds are formed between water molecules and the ions. These bonds are called ion–dipole bonds. Water is a polar molecule. The δ– oxygen atoms in water molecules are attracted to the positive ions in the ionic compound. The δ+ hydrogen atoms in water molecules are attracted to the negative ions in the ionic compound
