What are the periodic trends?

• Atomic radius • Ionization energy • Affinity • electronegativity • Shielding affect

Atomic radii

• Defined as one-half the distance between the nuclei of identical atoms that are bonded together.

• ( draw picture)

Trends

• Radii decreases from left to right across a period. – Add protons, add p-e pull • Increases as you go down a family – Adding energy levels, layers – Exception Al- Ga – Table 5-13 page 141 – slide

Questions

• In period 3, which has the largest radius – Na, Mg, P, Cl – In family 2 which has the largest radius • Ca, Be, Ba, Sr

Ionization Energy

• The energy

required

to remove an electron from a neutral atom. (first ionization energy) • Pg 143 figure 5-15 • When you remove an electron from a neutral ion you form an ion. • Any process that results in the formation of an ion is ionization.

Trends

• Ionization energy increases from left to right across a period. – It gets harder and harder to remove an electron – Radius is smaller, the pull between nucleus and electron is greater.

– Noble gas – can’t remove the electron.

– Dips where electrons double up in an orbital.

Trends

• Ionization energy generally decreases as you go down a family.

– The radius is larger, the electrons are further away and are therefore held less tightly. – Shielding occurs – there are more energy levels that have electrons in them, they shield the outer electrons from the nuclear pull. – Show slide

Second ionization energy

• The energy required to remove a second electron from an atom ( ion). • Always requires more energy to remove the second and successive electrons than the first. • Table 1-3 pg 145

practice

• Element A has a first ionization energy of 419 kJ/mol. Element B has a first ionization energy of 1000 kJ/mol. – Are they in the s or p block?

– Which will most likely give up their electron?

Electronegativity

• Measure of the ability of an atom in a chemical compound to attract electrons. – Fluorine assigned a number 4 – Everything else is based off of that value.

Trend

• Family 18 exception • Family 1 is very willing to give up its electrons.

– Has a noble gas configuration if it does – Loosely held • Family 17 wants electrons – Fill the outer energy level – Stable

Trend

• As you go left to right across a period it electronegativity increases • As you go down a family electronegativity will decreases – Shielding affect – Electrons are further out, loosely held

practice

• Given the elements Ga, Br and Ca which has the highest electronegativity?

• Given 2s 2 2p 5 , 4d 10 5s 2 5p 5 , and 2s 2 2p 2 – Which is the most electronegative?

– Which two are in the same family?

Affinity and Electronegativity

• Both affinity and electronegativity measure an atom’s ability to attract electrons.

• Affinity is the energy change when an atom gains an electron • Electronegativity measures the ability of an atom to attract electrons.

Electron Affinity

• The energy change that occurs when an electron is

acquired

by a neutral atom.

• If energy is released when an atom gains an electron, the atom is more stable with the extra electron. This will be represented as a negative number – Cl- -361.7 k • Group 17 gains electrons readily.

affinity

• If energy is required to make the electron ‘stick’, then the atom is less stable.

• This is represented by a positive number for electron affinity or zero.

Stability

• Atoms will always want the most stable configuration; – A noble gas configuration – A filled sublevel – A half filled sublevel, 1 electron per orbital.

practice

• Given 2s 2 2p 5 , 4d 10 5s 2 5p 5 , and 2s 2 2p 2 Which has the highest electron affinity?

• Which family would you expect to have a greater electron affinity, family 2 or 16?

trends

• Not as regular as other trends.

• Affinity increases left to right across a period. (electrons are added more easily) • Affinity decreases down a family. Electrons add with greater and greater difficulty as you go down a family. – Less nuclear attraction – shielding affect

Ionic radii

• Cation – loss of an electron always causes a

decrease

in atomic radius. • Anion – gain of electrons always

increases

atomic radius

Trends

• Table 5-19 page 149 • Ionic radii decreases across a period. – Cationic radii decreases across a period then in family 15 radii start to increase. – Radii increases down a family.

Ion electron configuration

• examples

Valence electrons

• Outer level, highest level electrons.

• Electrons available to be lost, gained, or shared in the formation of chemical compounds.

Section review

• State and discuss the general period and group trends among the main group elements. – Radius – First ionization energy – Electron affinity – Ionic radius – Electronegativity • Among the main group elements, what is the relationship between the group number and the number of valence electrons?

• How do the periodic properties of the d block elements compare with hose of the main group elements?

Section review

• Among the main group elements,what is the relationship between the group number and the number of valence electrons?

• How do the periodic properties of the d block elements compare with hose of the main group elements?