Periodicity Trends in physical and chemical properties demonstrated by the periodic table of the elements

The Periodic Table Each horizontal row (“period”) represents a new energy level

The Periodic Table Elements in the same period have valence electrons in the same energy level

The Periodic Table So the energy level increases as you move down the periodic table one period at a time

The Periodic Table Each new energy level is further from the nucleus than the energy level below it

The Periodic Table Distance from the nucleus matters because at greater distances, the forces between charged particles decreases

The Periodic Table As you move across a period left to right, the energy level is the same but the atomic number increases (remember atomic # = # of protons)

The Periodic Table More protons will exert more force of attraction than fewer protons (assuming the same distance between them)

Periodic Trends There are a number of physical and chemical properties that we will examine that form trends as you move down and across the periodic table Atomic Size (Radius) The radius of an atom is the distance from the center of the nucleus out to the valence energy level Ionization Energy Ionization energy is the energy it takes to remove a single electron from a neutral atom Electronegativity Electronegativity is the relative force that an atom will exert on electrons from another atom when they bond together

Atomic Radius

Atomic Radius As you move down the table from top to bottom, valence electrons are at progressively higher energy levels Atomic Radius increases from top to bottom

Atomic Radius As you move across the table left to right the energy level is the same, but there is an increase in the number of protons More protons means more attraction to the electrons, pulling them closer Atomic Radius decreases from left to right in the same period

Ionization Energy

Ionization Energy As you move across the period, elements have the same valence energy level, but progressively MORE PROTONS

Ionization Energy More protons results in stronger attractions Stronger attractions result in more energy needed to take an electron

Ionization Energy Note that ionization energy increases across the period, but has a few dips at the points where new orbital types start to fill

Ionization Energy Note also that ionization energy is very high for the noble gases, and very low for the group 1 metals

Ionization Energy The noble gases not only have the largest number of protons in their period, they also have a stable electron configuration

Ionization Energy The group 1 metals are the elements that start a new period. A new period is a new energy level Further from the nucleus means less force of attraction, so easier to remove an electron

Electronegativity

Electronegativity The relative amount of force of attraction that an atom will have to electrons from another atom

Electronegativity High electronegativity indicates a strong hold on electrons the atom is sharing in a chemical bond Low electronegativity = weak hold on the electron pair

Electronegativity Difference If the two atoms have equal electronegativity, they will pull equally on the electron pair Electrons will be shared equally This is a nonpolar covalent bond If the two atoms have significantly different electronegativities they will not pull equally on the electron pair, so the sharing will not be equal This is either polar covalent or ionic bonding