Periodic Trends

What are the 4 periodic trends?

atomic radius, ionization energy, electron affinity, and electronegativity

AR stands for…

atomic radius

what is atomic radius?

the distance from the centre of an atom to its outer electron orbital

describe the 2 patterns of AR

• down a group, the AR will increase 

  • addition of energy levels

• right along a period, the AR decreases 

  • Electrons are added to the same energy level, and the shielding effect stays the same along the period

    • the stronger positive charge pulls the electrons closer to the nucleus

    • as a result the AR shrinks

describe AR with cations

the same net charge is distributed among less electrons, resulting in a greater force of attraction and a smaller radius 

describe AR with anions

the same net charge is distributed among more electrons, resulting in a weaker force of attraction and a larger radius

IE stands for…

ionization energy

what is ionization energy?

the amount of energy required to remove the outermost electrons

• Therefore:

  • the 1st IE removes energy from the 1st electron (easiest to remove due to the weak force of attraction and shielding effect)

  • the 2nd IE removes an electron from a 1+ cation

  • the 3rd IE removes an electron from a 2+ cation

Describe what proximity toward the nucleus means in IE

The closer the electron is to the nucleus , the stronger the force of attraction and the higher the IE.

describe the 2 patterns of IE

• down a group, the IE decreases

  • the addition of energy levels means the electron being removed is further from the nucleus (weaker force of attraction, can get snatched easily)

• right along a period, the IE increases 

  • the higher net charge means that there is a greater force of attraction by the valence electron to the nucleus, causing a higher IE

What is the exception to IE?

Filled and half filled sublevels have additional stability, therefore they have a higher IE and so removing them requires more energy than expected.

What must you remember about 2nd IE?

2nd IE (and so on) will always have higher values since you are now removing from a cation, however the patterns seen in the 1st IE will still be present but shifted by one position. 

EA stands for…

electron affinity

what is electron affinity?

the amount of energy released when an electron is added to an atom.

Why is energy released when you add an electron to an atom?

due to the increase in stability of an atom

describe the 2 patterns of EA

• down a group, EA decreases

  • the addition of energy levels means the electrons being added are further away from the nucleus and thus have a weaker force of attraction

• right along a period, EA increases 

  • the higher net charge means that there is a greater force of attraction by the valence electrons to the nucleus, causing a higher EA

What is the exception to EA?

Atoms that have half-filled and filled sublevels are already stable

• In the case of filled sublevels, energy is actually required to generate a new sublevel for the electron to be added

  • This means that the amount of energy released is significantly lower or will require energy to be added to force the atom to accept the electron

EN stands for…

electronegativity 

what is electronegativity?

a relative scale showing the ability of an atom to attract a shared pair of electrons.

describe the 2 patterns of EN

• down a group, EN decreases

  • the addition of energy levels means the electron pair being attracted are further from the nucleus, and so there is a weaker force of attraction

• right along a period, EN increases 

  • the sublevels become closer to being filled and “completing their set”,

  • closer to the nucleus as the net charge increases

What are the 2 ways we can measure electronegativity?

pauling’s scale and van arkel ketelaar triangle

What are the exception to EN?

Xe and Kr, are the only noble gasses with an EN value

pauling scale

• relative scale used to measure EN (requires bonds that can be measured)

• difference between EN values (ΔEN) to determine the type of bond between 2 atoms

  • < 0.4, non-polar

  • 0.4-1.7, polar covalent 

  • ≥ 1.7. ionic 

Van arkel ketelaar triangle

• another scale that uses EN to determine the type of bond

• average and difference EN between 2 atoms

• those values are used to find the type of bond on the graph

Coulomb’s law

F = (k q₁q₂) / d²

• F = force of attraction

• k = constant

• q₁ and q₂= charges involved (net charge and charge on e^-)