Periodic Trends

Types of Periodic Trends How elements differ as you move through the periodic table? Atomic Radius Ionic Radius Ionization Energy Electronegativity

Atomic Radius  The atomic radius is a measure of the size of an atom.  The larger the radius, the larger is the atom.

Trends in Atomic Radius  There is a general decrease in atomic radius from left to right, caused by increasing positive charge in the nucleus.

Atomic radius generally increases as you move down a group. The outermost orbital size increases down a group, making the atom larger.

Trends in Atomic Radius  The atomic radius decreases as you move across a period  Why?  Increased nuclear charge pulls the electrons in tighter

Group Trends in Atomic Radius  Atomic Radius increases as you move down a group  Why? The increasing number of electrons are in higher energy levels

Atomic Radius

Ionic Radius  Atoms can gain or lose electrons to form ions  Ion: an atom with a charge  Recall that atoms are neutral in charge,  If an electron is lost, then the overall charge is positive  If an electron is gained the atom becomes negative

Ionic Radius Trend Metals – lose electrons, which means more protons than electrons Nonmetals – gain electrons, which means more electrons than protons

Positive Ion (Cation) Formation  When atoms lose electrons  Radius always becomes smaller

Negative Ion (Anion) Formation  When atoms gain electrons  Radius always increasesWhy?  More electrons mean more electrostatic repulsion resulting in increased diameter.

Ionic Radius How do I remember this????? The more electrons that are lost, the greater the reduction in size. Li +1 Be +2 protons 3 protons 4 electrons 2 electrons 2 electrons 2 electrons 2 Which ion is smaller?

Ionic Radius How do I remember this??? The more electrons that are gained, the greater the increase in size. P -3 S -2 protons15protons 16 electrons 18electrons 18 electrons 18electrons 18 Which ion is smaller?

Ionic Radius

Ionization Energy  the amount of energy need to remove an electron from a specific atom  High Ionization Energy: atom is holding onto electrons very strongly  Low Ionization Energy: atom is holding electrons less tightly

Trends for Ionization Energy  Generally increases as you move across a period  because increased nuclear charge causes an increased hold on the electrons  Ionization Energy decreases as you move down a group  due to increasing atomic size

Trends in Ionization Energy

Electronegativity  The ability of an atom to attract electrons to itself when it is combined with another atom  Expressed in terms of a relative scale: fluorine is assigned a value of 4 and all other elements are calculated relative to this.  Noble gases have no values because of few chemical compounds

Electronegativity  Greater the electronegativity  the higher an atom’s ability to pull an electron to itself when it is bonded to another atom

Trends in Electronegativity  Electronegativity Increases as you move across a period  Electronegativity decreases you move down a group

Electronegativity

Another Summary