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 2s22p5 , 4d105s25p5, and 2s22p2

– 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 2s22p5 , 4d105s25p5, and 2s22p2

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?