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The Periodic Table Periods, groups, and trends The Bohr Model • After Rutherford’s model of the atom, Neils Bohr created our modern atomic model • He suggested that the electrons of an element are arranged in energy levels or “energy shells” • Using this model helps us understand the periodic table of elements What is The Periodic Table of Elements? • An arrangement of the elements Periodic Law • “When the elements are arranged according to their atomic numbers, elements with similar properties appear at regular intervals” • When elements are arranged by their atomic numbers, groups of elements begin to have similar characteristics Organization of the Periodic Table • Elements in each column of the periodic table have the same number of electrons in their outer shell – Called “valence electrons” • Elements with the same number of valence electrons react in similar ways Periods • A horizontal row on the periodic table of elements is called a period Groups • A vertical column of the periodic table is called a group • Elements in a group share similar chemical properties Main Group Elements • Elements in groups 1,2, and 13-18 are known as main group elements • Electron configurations of each element are regular and consistent • Main group elements include: – – – – Alkali Metals Alkaline Earth Metals Halogens Noble Gases Alkali Metals – Group 1 Alkali Metals – Group 1 • They are metals that react with water – They are very reactive • Never found in nature as “pure elements” but are found as compounds • Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium Alkaline Earth Metals – Group 2 Alkaline Earth Metals – Group 2 • Slightly less reactive than Alkali Metals • Have 2 valence electrons Halogens – Group 17 Halogens– Group 17 • The most reactive group of the non metal elements • They have 8 valence electrons • React with most metals to produce salts – Sodium and Chlorine – Table Salt Noble Gases – Group 18 Noble Gases – Group 18 • Group 18 elements are called Noble Gases • Have a very low reactivity Hydrogen • The most common element in the universe • It only has one proton and one electron so it is unlike any other element • Reacts with many other elements Transition Metals • These occupy the center of the periodic table Transition Metals cont. • Extremely unreactive • Some almost never form compounds with other elements Metals • All Metals are excellent conductors of electricity – Most often distinguishes metals from non-metals • Can be brittle or malleable Metalloids • Found on the table between metals and non metals Metalloids • All metalloids are solids at room temperature • Have some characteristics of metals and have some characteristics of non-metals Non-Metals • Many non-metals are gases at room temperature • Poor conductor of heat and electricity • Found on the right side of the periodic table Periodic Trends • The arrangement of the periodic table reveals trends in the properties of the elements – A trend is a predictable change or characteristic • Understanding a trend among elements in a group or period enables you to make predictions about their behavior Ionization Energy • Ionization energy is the energy required to remove an electron from an atom Ionization Energy Cont. • Ionization energy decreases as you move down a group Ionization Energy cont. • Ionization energy increases as you move from left to right across a period Melting Point • Metals generally posses a high melting point • Most nonmetals possess low melting points Electronegativity • Refers to how strongly each atom attracts other electrons • An atom with higher electronegativity will pull on the electrons more strongly than another atom will • Electronegativity decreases as you move down a group • Electronegativity increases from left to right across a period