Unit 2: Periodic Table Trends
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What are the 6 main trends in the periodic table covered in this unit?
Atomic radii, ionization energy, ionic radii, electron affinity, electronegativity, reactivity
What is the nuclear charge?
Positive charge from the nucleus/# of protons
What are shielding electrons?
The electrons located between the nucleus and the valence electrons
What is the effective nuclear charge?
The attractive force of the nucleus that is felt by valence electrons
How is Zeff. calculated?
Nuclear charge - shielding electrons
What does a higher Zeff mean?
A stronger pull on electrons
Why do valence electrons feel less of an attractive force from the nucleus?
Because they are at higher energy levels which means they are further from the nucleus resulting in less of an electrostatic force and because the shielding electrons repel the valence electrons
What is the general trend for the atomic radii in the periodic table?
Increases down a group, decreases across a period
Why does the atomic radii generally increase down a group?
Due to higher energy levels further from nucleus and there is an increase in shielding electrons repelling valence electrons
Why does atomic radii decrease across a period?
Due to an increase in nuclear charge while shielding and energy level remains the same (increase in Zeff across period)
What is the exception to atomic radii decreasing across a period?
There can be a slight jump up when moving into p block due to slightly higher energy and different shape
What are the two ways of measuring atomic radius?
Bonding diameter/covalent radius and non bonded radius/Vander waals radius
What do you compare when comparing atomic radii?
Energy level, shielding electrons, and effective nuclear charge
Why does ionization energy decrease going down a group?
because the electrons are in higher energy levels and further from the nucleus and the radius is bigger which means the electrons are less attracted to the nucleus
Why does ionization energy increase across a period?
because the atomic radius is decreasing due to same energy level and same shielding but greater effective nuclear charge which pulls electrons in tighter
What are the exceptions to the trend in ionization energy?
There is a decrease from group 2 to group 13 due to change to p block which is slightly higher energy and easier to ionize, and there is a decrease from group 15 to group 16 because group 15 has a half filled p orbital while group 16 has one orbital with paired electrons which require pairing energy therefore is easier to ionize
What does a parent atom become after losing electrons?
a smaller cation with a larger effective nuclear charge
What does a parent atom become when it gains electrons?
a larger anion with a smaller effective nuclear charge
How does the trend in ionic radii differ from the trend in atomic radii?
at group 14, there is an increase in size of radii due to the ability of the atoms to become anions rather than cations
What is electron affinity?
the change in energy when one mole of electrons is added to one mole of a neutral atom in the gas state
What does a larger number mean for electron affinity?
the more likely the atom is to gain electrons/higher affinity
What does a negative electron affinity mean?
the process is exothermic/energy is being released
Why do noble gases have no values listed for electron affinity?
because they do not gain electrons
Why are there second electron affinity values positive for oxygen and sulfur?
because the electron to electron repulsion must be overcome by adding energy