Periodic Trends

The Periodic Table Rows = periods (left to right) Columns: families or groups(up & down) Alkali Metals (Group 1 or IA) Alkaline Earth Metals (Group 2 or IIA) Halogens (Group 17 or VIIA) Noble Gases (Group 18 or VIIIA) A-group families = main group or representative elements B -group = transition elements or metals

The periodic table

Metals, Nonmetals, and Semiconductors What makes an element a metal? A substance that has a tendency to lose electrons to empty its valence shell. What makes an element a nonmetal? A substance that has a tendency to gain electrons to fill its valence shell. A few elements exhibit properties of both metals and nonmetals. These elements are called metalloids or semiconductors

Metals, nonmetals and semiconductors

Metals, nonmetals and semiconductors Noble gases - filled shells, stable elements 1A, 2A, & 3A Groups Lose outer electrons to become positive ions - cations All elements in these groups are metals 5A, 6A & 7A Groups Tend gain electrons and form negative ions - anions All elements in these groups are nonmetals Semiconductors- intermediate between metals and nonmetals

Oxidation Numbers of Ions Formed Oxidation number refers to the charge on the ion formed from atoms in a particular group

Atomic Radius Remember, electrons are added one at a time moving from left to right across a period As this happens, the electrons of the outermost shell experience increasingly strong nuclear attraction Electrons become closer to the nucleus

Atomic Radius The increased number of protons going across a given period increase the pull on the outer shell electrons Shrinking atom Going down a group, each new element represents a new shell of electrons and thus a fatter element! Generally, the atomic radius decreases across a period from left to right and increases down a given group

Relative Atomic Radii

Ionization Energy Ionization energy- energy required to completely remove an electron from a gaseous atom The closer an electron is to the nucleus, the more difficult it will be to remove Greater ionization energy

Ionization Energy Ionization energies increase moving from left to right across a period (decreasing atomic radius) and decrease moving down a group (increasing atomic radius)

Ionization Energy

Ionization Energy Metals have lower ionization energies than non-metals that share their period or group. The lower the ionization energy for metals, the more reactive they will be. Non-metals have higher ionization energies than metals that share their period or group. The valence shell is closer to the nucleus, thus electrons experience a stronger nuclear force of attraction.

Electronegativity Electronegativity is a measure of the attraction of an atom for the electrons in a chemical bond AKA- electron affinity The higher the electronegativity of an atom, the greater its attraction for bonding electrons The atom wants to bring in electrons Electronegativity increases from left to right across a period and decreases as you move down a group

Electronegativities of the representative elements

Electronegativity The smaller the atom the easier it is to attract electron and the more reactive a non-metal will be. High electronegativity Atoms with low ionization energies have low electronegativities because their nuclei do not exert a strong attractive force on electrons

Summary

Ionic Radius- Cations Cations are formed when an atom gives up an electron Positive ion All metals form cations Down a group, the ionic radius of cations increases Extra shells of electrons

Ionic Radius- Cations Across a period (within cations) ionic radius will decrease Fewer electrons, same number of protons pulling them in Cations always have a smaller radius than the atoms they formed from

Ionic Radii (Cations)

Ionic Radius- Anions Anions form when an atom gains electrons to reach an octet Overall negative charge Nonmetals form anions Down a group, ionic radius of anions increases More shells of electrons

Ionic Radius- Anions Across a period, ionic radius of anions decreases Anions always have a larger radius than the atoms they came from Adding electrons to the same number of protons

Ionic Radii (Anions)