Regents Chemistry Unit 2 The Periodic Table Text Chapter 5

Transcription

1 Regents Chemistry Unit 2 The Periodic Table Text Chapter 5

2 I. Historical Development of the Periodic Table

3 Stanislao Cannizzarro- In1860 presented a convincing method for accurately measuring relative masses of atoms and this method allowed chemists to agree on standard values for atomic masses and initiated a search for relationships between atomic mass and other properties of the elements

4 Dimitri Mendeleev (1869) Mendeleev produce the first orderly arrangement of the periodic table, of all 60 elements known at that time. He arranged the elements in order of increasing atomic mass. As he started each row he noticed that the chemical properties of the elements repeated. He placed elements in the new row directly below elements of similar chemical properties in the preceding row. Mendeleev s table contained gaps that elements with particular properties should fill. He predicted the properties of the missing elements. He was the first to do this so chemists accepted his periodic table of elements. He also gave these elements provisional names. some discrepancies he could not explain still existed

5 Henry Moseley (1911) an English Chemist discovered a previously unrecognized pattern, that spectral lines correlated to atomic numbers (nuclear charge), not atomic mass. When the elements were arranged by atomic number Mendeleev s discrepancies disappeared and elements with similar properties appear at regular intervals. This was the basis for the modern periodic table. Mosley s work led the modern definition of atomic number

6 The Periodic Law - repeating chemical and physical properties of the elements are functions of their atomic numbers.

7 II. Organization of the Periodic Table Groups are the vertical rows elements in the same group have the same number of valence electrons Periods are the horizontal rows elements in the same period have the same number of occupied principle energy levels (PEL s)

8 III. Tour of The Periodic Table The Main Group Elements (representative elements) - elements in group 1,2 and the electron configurations of these elements are regular and consistent.

9 The Alkali Metals Make Up Group 1 they react with water to make alkaline solutions. They are usually stored in oil to keep them from reacting with the O 2 and H 2 O in air. They are highly reactive because of a single s electron in its valence shell. They are never found in nature as a pure element, but as a fused salt. Ex. NaCl.

10 The Alkaline Earth Metals Make up Group 2 are highly reactive and are not found in nature as pure elements, but as fused salts. *Groups 1 & 2 are known as the s block because the s orbital is being filled with electrons. As the atomic number of group 1 & 2 increases the reactivity increases due to the outermost shell increasing (additional PEL) Fr is the most reactive metal b/c it has the lowest IE of the group taking less energy to lose an electron during a Rxn.

11 Transition Metals Occupy the Center of the Periodic Table groups d- block because the d orbitals of the preceding PEL are being filled with electrons. transition elements form colored solutions *MUST KNOW THIS!

12 The Halogens, Group 17, Are Highly Reactive non-metals are ideally suited to bond with the alkali metals. They exist in all 3 phases of matter. The halogens are all diatomic molecules. Does not include At b/c it is a synthetic element prepared in very small quantities, most of its properties are estimated, but is known to be a solid.

13 The Noble Gases, Group 18, Are Unreactive have a full outer most shell of electrons. Kr, Xe and Rn can react with O & F due to their large size. Noble gases are referred to as monatomic molecules. *Groups are known as the p block because the p orbitals are being filled

14 Lanthanides fill f-orbitals and are called the f block. Lanthanides are called this because their atomic numbers follow the element lanthanum. However, on the basis of their properties, the elements from cerium to lutetium (atomic numbers 58-71) do not belong in the vertical groups of the periodic table. In fact, the properties of these elements are so similar that it is difficult to tell them apart. These elements are known as the rare earth elements. To avoid having another gap in the periodic table, these elements are placed in a separate row at the bottom of the table

15

16 Actinides also fill f-orbitals and are also called the f block. The actinides are called this because they follow the element actinium. In this series we reach the last of the naturally occurring elements, uranium, atomic #92. All the elements beyond uranium are synthetic and are not found in nature. The stability of the synthetic elements generally decreases as atomic number increases. Both Actinides and Lanthanides are referred to as Inner transition elements.

17 Current Periodic Table

18 Properties of Metals generally hard; most are solids except Hg High melting points Malleable can shape and bend; pound Ductile can be stretched into a fine wire Have luster are shiney Form positive ions by losing electrons Good conductors of heat and electricity Have low ionization energies Have low electronegativies

19 Other Properties of Metals *FYI Alloys a mixture of 2 or more metals Brass is Cu and Zn and is harder than Cu and corrosion resistant; Sterling Silver is Cu and Ag; Steel is C and Fe Stainless Steel is C and Fe plus Cr Amalgam a mixture where another metal is dissolved in mercury

20 Properties of Non-metals poor conductors of heat and electricity lack luster in the solid phase are brittle in the solid phase have high ionization energies have high electronegativities gain electrons to form negative ions most are gases or molecular and network solids at room temp.

21 Metalloids (semi-metals) Metalloids have 2 sides of the staircase touching them B, Si, As, Te, Ge, Sb *Exceptions are Al & Po. Po is radioactive and Al has more metallic properties than non metallic

22 IV. Trends in the Periodic Table Ionization Energy the energy required to remove the most loosely bound electron Ionization Energy Decreases as You Move Down a Group b/c each element has more occupied principle energy levels than the one above it. The inner electrons shield the outermost electrons from the full attractive forces of the nucleus. This electron shielding causes the outermost electrons to be held less tightly to the nucleus. Ionization Energy Increases as You Move Across a Period b/c the number of protons (atomic No.) increases, the nuclear charge increases, which attracts outer electrons in the same energy level.

23 An electron ion Ionization energy

24 Electronegativity-how much an atom wants an electron. Values found on Table S Electronegativity Decreases as You Move Down a Group b/c an additional PEL is added increasing the distance between the nucleus and the outermost PEL Electronegativity Increases As You Move Across a Period because the nuclear charge increases (number of protons) and electrons are more attracted

25 Electron Electronegativity Electronegativity Low electronegativity (Fr) High electronegativity (F)

26 Atomic Radius is defined as the bond radius half the distance from center to center of two like atoms that are bonded together. Values found on Table S Atomic Radius Increases as You Move Down a Group b/c you are adding an additional PEL Atomic Radius Decreases as you Move Across a Period b/c the nuclear charge increases (number of protons) pulling the outermost electrons closer to the nucleus make the atom smaller

27 Other Periodic Trends Periodic Trends In Ionic Size An ion is a charged particle. An atom becomes an ion by gaining or losing an electron. All metals form positive ions (cations) by losing electrons and have a smaller ionic radius than their corresponding atomic radius. All nonmetals form negative ions (anions) by gaining electrons and their ionic radius is larger than their atomic radius.

28 Metallic Character Trends Nuclear charge trends-the greater the nuclear charge of an atom, the greater its attraction for electrons. the elements on the left of any period have a weaker hold on their valence electrons than those on the right side and tend to be more metallic in character.