Chemistry - Periodic trends

What do elements in the same group have the same number of?

valence electrons

How do valence electrons change as you go across a period?

they increase by one

What is the Effective Nuclear Charge (ENC)?

the charge experienced by valence electrons after accounting for shielding electrons

What are shielding electrons?

electrons in shells that are not in the valence shells

Describe the shielding effect.

inner electrons block the valence electrons from the full positive pull of the nucleus

How does ENC change down the group?

ENC stays the same down the group and equals the group number

How does ENC change across a period?

ENC increases by one

Define atomic radius (AR).

the distance from the center of the atom to the valence shell

What happens to AR as you go down a group?

the AR increases due to more shells and shielding electrons

How does AR change across a period?

the AR decreases because ENC increases so valence electrons are pulled inward strongly

What is ionization energy (IE)?

the energy required to remove a valence electron from an atom or ion in its gaseous state

How does IE change down a group?

IE decreases because electrons are harder to remove

What happens to IE as you go across a period?

IE increases because electrons are easier to remove

Define electron affinity (EA).

the energy absorbed or released when an atom gains an electron to form a negative ion

How does EA change down a group?

EA decreases as atoms get larger and have more shells so there is a smaller charge in energy when they gain electrons

What happens to EA as you go across a period?

EA increase because the atom attracts an added electron more strongly

What is electronegativity (EN)?

an indicator of the relative ability of an atom to attract shared electrons of a bonding pair

How does EN change down a group?

EN decreases because the nucleus has less pull on shared electrons

How does EN change across a period?

EN increases because the atom attracts shared electrons more strongly

What is the trend for reactivity in non-metals down a group?

reactivity decreases because it becomes harder to gain electrons

How does non-metal reactivity change across a period?

reactivity increases because non-metals want to gain electrons

What is the trend for reactivity in metals down a group?

reactivity increases because it becomes easier to lose electrons

How does metal reactivity change across a period?

reactivity decreases because metals have a harder time losing electrons

What happens to ionization energy as you go down a group?

ionization energy decreases because atomic radius increases

What is the relationship between atomic radius and ionization energy as you go down Group $1$?

as you go down, atomic radius increases and ionization energy decreases

Which element has a larger atomic radius, Lithium or Fluorine?

lithium has a larger atomic radius than Fluorine; ENC affects the size

What happens to electronegativity and atomic radius as you go across a row?

electronegativity increases while atomic radius decreases

What is the main story across a period regarding ENC?

ENC increases, leading to a stronger pull on valence electrons causing AR to decrease

What happens to atomic radius and ionization energy as you go down a group?

atomic radius increases, while ionization energy decreases due to decreased nucleus pull on valence electrons