periodic trends

atomic radius 19-21/2/25, ionization energy 21-25/2/25, electron affinity and electronegativity 26/2/25, Zeff

atomic radius

Distance from the nucleus out to the valence shell

dependent and independent variable in AR graph

• Atomic # = independent variable 

• Atomic radius = dependent variable 

nuclear charge (Z)

•  positive charge present in the nucleus of an atom

• keeps electrons in place

shielding

• the repulsion of outer electrons by inner electrons 

• stronger than sideways repulsion

effective nuclear charge

• Net attraction of electrons to the nucleus 

• Z_eff = Z (nuclear charge) - shielding

sideways repulsion

• repulsion between electrons on the same shell

• causes spaces between electrons

• weaker than shielding

• mr.moniz term

trend of Z_eff

• across a period (left to right): protons increase while inner shielding electrons always stay the same, so effective nuclear charge also increases

• down a group: a new shell is added, all inner orbits become shielding electrons, increased shielding and low inner p+:e- causes more repulsion than attraction, so effective nuclear charge decreases

trend of atomic radius

• across a period (left to right): protons increasing, inner shielding electrons stay the same, so Z_eff increases, causes increased attraction, electrons pulled in more closely, atomic radius decreases

• down a group: AR does not increase because of an added orbit. A new valence orbit is added, inner orbits become shielding electrons, more repulsion, the p+:inner e- ratio decreases, valence is less drawn to the nucleus, atomic radius increases

ionization energy

• minimum amount of energy required to remove an electron from a neutral element in the gaseous state producing a +1 cation

• since minimum, it removes electron from valence shell

• X_g + IE = X_g⁺ + e- (free electron)

trend of ionization energy

• across periods (left to right): Z_eff increases, shielding stays the same while p+ increases, causing more attraction, more energy needed to remove e-, p+:inner e= ratio increasing, ionization energy increases

• down a group: Z_eff decreases, new shielding orbit, more repulsion than attraction, less energy required dislodge e-, p+:inner e- ratio decreases, ionization energy decreases

what does the spike in the ionization energy graph show?

• jumps to inner orbit

• inner electron is removed

• requires proportionally much more energy to remove the inner electrons because the effective nuclear charge has drastically increased 

multiple ionization energies

• minimum energy required to remove subsequent electron to form a cation in an element in its gaseous state

• X_g⁺ + IE_2nd = X_g²⁺ + e- (+2 cation and free electron)

• change is discontinuous

• each subsequent electron needs more energy to be removed

why is more IE needed overtimr?

• Sideways repulsion is decreased because the first electron was removed from valence shell

• nuclear charge is more effective because the sideways repulsion decreases

• overall repulsion decreases so the attraction is more effective

• attraction itself does not increase but bc repulsion is less, overall attraction increases

electron affinity

• energy released by a neutral atom in the gaseous state when it attracts an electron to form a -1 anion (negative energy)

•  X_(g) + e^-  → X^-_(g) + E.A

why is energy releases when an electron is added to a neutral atom

• the electron is attracted to the positively charged nucleus

• meteor analogy: attracted to earth, pulled by gravity, accerlates towards earth, potential energy is being converted to kinetic energy, energy converted to heat and sound

• electron attracted to nucleus, falling into atom and losing potential energy

• energy released as light once electron reaches atom, this energy is EA

what does it mean if an electron needs to be pushed into an atom (IE)?

• that means there is repulsion (from the other electrons there)

• repulsion to add electron: negative electron affinity written as a positive number

electronegativity

a calculated average of measurements indicating the tendency of an element to attract an electron charge towards it in a compound

What factors allow metallic elements to form ions where they have lost their valence electrons?

• Metallic elements effective nuclear charge is low

• IE is also low

• The proton to inner electron ratio is lower

• so metallic elements are more likely to form cations because they have lower ionization energy

stable

how difficult is something to change, is it difficult or easy to change 

electron affinity

energy released by a neutral atom in the gaseous state when it attracts an electron to form a -1 anion, exothermic

electronegativity and electron affinity trend

• across a period (left to right): both increase, EN: more protons, unchanged shielding, Z_eff increases, more attraction, greater tendency to attract electron. EA: more energy given off when anion forms

• down a group: both decrease, EN: new shielding, more repulsion than attraction, tendency to gain electron is less. EA: greater repulsion, less energy released when anion is formed

• noble gasses do not attract electrons because the valence shell is full, and much more energy is needed to overcome the repulsion for an electron to go into the next shell

• noble gasses have high IE and are less likely to lose an electron

all trends general

• left to right: Z_eff increases, AR decreases, IE increases, EN and EA increases

• down a group: Z_eff decreases, AR increases, IE decreases, EN and EA decreases