Periodic Trends

Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends using above factors. Include: atomic / ionic radii, ionization energy, electronegativity.

The force on an electron will affect its position around the atom The force on an electron will affect its position around the atom. The force depends on 3 factors: Nuclear charge - more protons, more attraction. Distance – further apart two charges are, lower their force of attraction (Coulomb’s Law). Shielding Effect - Inner electrons shield the force of the nucleus from outer electrons.

ATOMIC RADIUS Size of atoms tends to vary from substance to substance due to different interaction. Measured as half the distance between two nuclei when two like atoms are bonded together.

Decrease Across same quantum level (same size / n value) increase in nuclear charge ( pulls orbitals closer) Increase Down new quantum level (larger size / n value) increased shielding (decreased force on outer e-)

Na: 11 p+ 11 e- Cl: 17 e- 17 p+

IONIC RADIUS Ion size differs from atom size.

*Same* basic trend as atomic radius.

Positive ions - smaller radii increased proton - electron balance (lost e-) more nuclear charge on remaining e- sometimes loss of a quantum level. Negative ions - bigger radii decreased proton - electron balance (gain e-) Less nuclear charge on remaining e- repulsion of additional e- causes expansion.

+ - Na Cl

A(g) + energy → A+(g) + e− Ionization Energy Energy required to remove an electron from an atom forming an ion – energy depends on force on e-. A(g) + energy → A+(g) + e− There are multiple ionization energy values for each element – one for each electron being removed. A+(g) + energy → A+2(g) + e−

Increases Across increased nuclear charge (increasing p+ number) same quantum level Decreases Down new quantum levels (increased distance) increased shielding (decreases force on outer e-)

+ Na Cl

Na Cs

IE increases with each electron removed Increased proton-electron ratio (small change) Less shielding (small change) Lower quantum level – closer (BIG change)

Electronegativity Attraction an atom has for bonding electrons. bigger the number, the harder they pull Periodic Trend: EN increases across the table and decreases down.

Na: Cl: WEAKER nuclear charge. STRONGER nuclear charge. Less attraction - large radius. STRONGER nuclear charge. More attraction - small radius. Na: Cl: Lower ionization energy. Lower Electronegativity. HIGHER ionization energy. HIGHER Electronegativity.

- + Large enough difference – ionic bonds form. The greater the electronegativity difference the more polar the bond. δ- δ+ H C H Cl H Polar covalent non-polar covalent Large enough difference – ionic bonds form. - +

EN Difference Bond Type Percent Ionic less than 0.4 non-polar covalent 0% − 5% 0.4 − 1.9 polar covalent 5% − 60% greater than 1.9 ionic > 60%

CAN YOU / HAVE YOU? Describe factors that affect electron position around a nucleus. Include: nuclear charge, distance, shielding. Explain periodic trends using above factors. Include: atomic / ionic radii, ionization energy, electronegativity.