# What are the periodic trends?

## Presentation on theme: "What are the periodic trends?"— Presentation transcript:

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 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?