10. PHYSICAL PERIODICITY Flashcards
How is the covalent radius of an atom found
- the distance between the two nuclei of the same type of atom in a covalent bond can be determined
- this can be divided by two to arrive at the single covalent radius
Why are mainly covalent radii used
- can be obtained for most elements
- so provide the best data for comparison purposes
Why do the noble gases in Group 18 not have a covalent radius
because they do not form bonds with each other
How are the van der Waals’ radii found
- the distance between the nuclei of two neighbouring touching atoms that are not chemically bonded together can be found
- this can be divided by two to arrive at the van der Waals’ radius
Why is the value of the van der Waals’ radius higher than the single covalent radius of any element
because there is no overlap of electron clouds in van der Waals’ radii
What property of SO2 enables it to act as a food preservative
- reducing agent
- kills bacteria
What is the periodic pattern of atomic radii
atomic radii decrease across the period
Why do atomic radii decrease across a period
- across the period, the nuclear charge increase as the number of protons increases
- the extra electron is added to the same principal quantum shell
- the shielding effect remains roughly constant
- the greater attractive force exerted by the increasing positive nuclear charge on the outer electrons pulls them in closer to the nucleus
Explain the difference in size between the cations and their corresponding atoms
- cation contains fewer electrons than corresponding atom
- decreased shielding effect on outer electrons
- increased attraction by nucleus
Variation in ionic radii from Na+ to Si4+
- ionic radii decrease
- the greater attractive force exerted by the increasing nuclear charge on the valence electrons pulls them in closer to the nucleus
Variation in ionic radii from P3- to Cl-
- ionic radii decrease
- the greater attractive forces exerted by the increasing nuclear charge on the valence electrons pulls them in towards the nucleus
Explain the difference in size between the anions and their corresponding atoms
- anion contains more electrons than corresponding atom
- increased repulsion between the electrons
- nuclear charge remains constant
- decreased nuclear attraction
Why does melting point increase in the metals across a period
- the bonding is metallic
- the strength of the bonding increases/ the electrostatic forces of attraction between the ions increases
- as the number of delocalised electrons increases
Why does electrical conductivity increase in the metals across a period
- the number of delocalised electrons increases
- more electrons are available to drift through the structure when a potential difference is applied
Why does silicon have the highest melting point in the period
- silicon has a giant covalent structure
- the Si atoms are bonded to each other with strong covalent bonds
- the covalent bonds require a large amount of energy to break