periodicity

Question 1

what are the trends in the atomic radius across a period?

Answer 1

decreases because:
-outer electrons are in the same shell
- more protons in nucleus
- same amount of shielding
- so stronger attraction between nucleus and outer shell electrons
- so outer shell electrons pulled closer to nucleus
- less distance

Question 2

what are the trends in the atomic radius down a period?

Answer 2

increases because:
- more shells/ energy levels
- greater distance between nucleus and outer electron
- increased amount of shielding
- so weaker attraction between nucleus and outer shell electrons
- so outer shell electron further away

Question 3

what is the definition of electronegativity?

Answer 3

power of an atom to attract the 2 electrons in a covalent bond

Question 4

what is the trend in electronegativity across a period?

Answer 4

increases:
- more protons in nucleus
- smaller atomic radius
- so stronger attraction between nucleus and 2 electrons in covalent bond

Question 5

what is the trend in electronegativity down a group?

Answer 5

decreases:
- more shells/more shielding
- larger atomic radius
- so weaker attraction between nucleus and 2 electrons in covalent bond

Question 6

what is the ionisation energy trend down a group?

Answer 6

decreases:
- more shells/energy levels
- increased amount of shielding
- greater distance between nucleus and outer electron
- so weaker attraction between nucleus and outer electrons
- so less energy required to remove one electron from outer shell

Question 7

what is the trend in ionisation energy across a period?

Answer 7

increases but there are 2 anomalies:
-more protons
-same shell
-atoms gets smaller
-therefore stronger attraction from nucleus to electron in outer shell

Question 8

why does the element Al in period 3 doesn’t fit the trend?

Answer 8

• there is a small drop between Mg and Al.
• Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the the 3p subshell
  -Als electron is slightly easier to remove because the 3p electrons are in a higher energy level

Question 9

why does the element sulfur in period 3 doesn’t fit the general trend?

Answer 9

• sulfurs outer electron is being paired up with another electron in the same 3p orbital
• when the second electron is added to an orbital there is a slight repulsion (electron pair repulsion)between the 2 negatively charged electron which make the second electron easier to remove

Question 10

what is the definition of periodicity?

Answer 10

the repeating pattern of physical or chemical properties going across the periods

Question 11

what’s the melting/boiling point trend across period 3?

Answer 11

• increases
• GML bonds increases (Na, Mg + Cl) making the ions smaller across the period
• silicon has the highest melting point as its a GCL. Many covalent bonds are stronger than metallic bonds so require more energy to break
  -P4, S8, Cl2 are simple covalent molecular so it has VDW and intermolecular forces so are weaker than metallic and covalent bonds
• S8>P4>Cl2 this is because S8 has more electrons so has stronger VDW forces between molecules
  -Ar is monatomic. It consists of very weak VDW forces between atoms