Dmitri Mendeleev In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for elements known to date. The periodic table is based on the similarity of properties and reactivities and atomic masses exhibited by certain elements. Later, Henri Moseley ( England, ) established that each element has a unique atomic number, which is how the current periodic table is organized.

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Periodic Table: Metallic arrangement Layout of the Periodic Table: Metals, Nonmetals, and Metalloids. Metalloids Nonmetals Metals

Across the Periodic Table Periods: Are arranged horizontally across the periodic table (rows 1-7) 2nd Period 6th Period

Down the Periodic Table Group or Family: Are arranged vertically down the periodic table (columns or group, or 1-8 A,B) These elements have the same number electrons in the outer most shells, the valence shell. Alkali Family: 1 e- in the valence shell Alkali Family: 1 e- in the valence shell Halogen Family: 7 e- in the valence shell Halogen Family: 7 e- in the valence shell

Families of the Periodic Table Alkali Alkaline (earth) Transition Metals Noble Gas Halogen Inner Transition Metals

Periodic Table: electron behavior The periodic table can be classified by the behavior of their electrons Anions (non- metals)- Tend to gain electrons Cations (metals)- Tend to lose electrons Oxidation States

Trends in Atomic Radius –Atomic and Ionic Radii: the size of the atom/ion; –Atomic size generally increases as you move down a group. –Atomic size generally decreases as you move from left to right across a period. Why? –As you move across a period to the right, the nucleus is becoming more positive. Therefore it can hold electrons more tightly. –As you go down a group, more & more orbitals are being added so the atom gets larger. The largest atoms are in the lower left corner. (Some exceptions.)

Atomic Radii Trends

Atomic Radius

Refer to a periodic table and arrange the following elements in order of increasing atomic radius: Br, Se, Te. 35 Br 34 Se 52 Te Te is larger than Se. Se is larger than Br. Br < Se < Te Trends in Atomic Radius

Ionic Radius When an atom gains or loses an electron, it becomes an ion. When an atom forms an ion, the size of the atom is changed. Positive ions (cations) are always smaller than the neutral atoms from which they form. (loss of electrons)

Negative ions (anions) are always larger than the neutral atoms from which they form. (Gain of electrons) Metals tend to form cations and nonmetals tend to form anions.

Trend in Ionic Radius 1.Anions (negative ions, gained electrons) are larger than their respective atoms. Cl->Cl 2.Cations (positive ions, lost electrons) are smaller than their respective atoms. Na+ < Na 3. In general iconic radius decrease from left to right

Ionic Radius

Trend in Ionization Energy The energy required to remove the valence electron from an atom. Largest toward NE corner of PT since these atoms hold on to their valence e- the tightest.

The size of each sphere indicates the size of the ionization energy in the figure below. Ionization Energy Trends

Ionization Energy

Trends in Ionization Energy Group Trends – –Ionization energy generally decreases as you move down a group of the periodic table. (Bigger atom = less ionization energy) –Ionization energy generally increases as you move from left to right across the periodic table.

More on Ionization Energy Can more than one electron be removed? Yes—these are the 2 nd ionization energies, 3 rd ionization energies, etc. (IE 2, IE 3, etc.) Usually it takes more energy to take away the 2 nd and 3 rd electrons as the remaining + charge in the nucleus “holds” the remaining electrons tightly. Some atoms will lose electrons easily until they have the same electron configurations as Noble Gases.

Refer to a periodic table and arrange the following elements in order of increasing ionization energy: As, Br, Sb. Sb is smaller than As. As is smaller than Br. Ionization energies: Sb < As < Br 35 Br 33 As 51 Sb Trends in Ionization Energy

Periodic Table: electron behavior The periodic table can be classified by the behavior of their electrons

Electronegativity Trends

Trends in Electronegativity Electronegativity – the tendency for the atoms of the element to attract electrons when they are chemically combined with atoms of another element (form bonds). electronegativities. (highest = fluorine) Periodic Trends: Electronegativity generally decreases as you move down a group. Electronegativity generally increases as you move left to right on the periodic table (excluding the noble gases)

Electronegativity

Valence Electrons & Oxidation Numbers Valence electrons are the electrons in the outside shell that are available for chemical reactions & bonding. Normally, only the outside/outermost s & p orbital are considered valence electrons. This means that the Transition metals are skipped. Oxidation numbers: When atoms form ions, they tend to gain or lose a set amount of electrons based on their position in the periodic table. Make sure you have this on your periodic table –Pattern for the main group elements is: +1 +2, +3, depends, -3, - 2, -1, 0

Objective #3: Define valence electrons, and state how many are present in atoms of each main-group element. Valence Electrons: electrons available to be lost, gained, or shared in the formation of chemical compounds For main-group elements, the valence electrons are the electrons in the outermost s and p sublevel

Summary of Trend Periodic Table and Periodic Trends 1. Electron Configuration 2. Atomic Radius: Largest toward SW corner of PT 3. Ionization Energy: Largest toward NE of PT

Questions Of the following elements, which has the greatest atomic radii? Ca, Cl, or Br –Calcium List the following elements in order of increasing electronegativity (from least to most). Ca, Mg, Rb –Rubidium, Calcium, Magnesium Of the following elements, which has the greatest electron affinity? Si, Se, S –Sulfur List the following elements in order of decreasing ionization energy (from most to least) Al, Ar, P –Ar, P, Al Of the following elements or ions, which has the greatest radii? Cl, Cl -1, Br, Br -1 –Br -1