Chapter 5. Periodic Law.

Transcription

1 Chapter 5 Periodic Law

2 Chapter 5.1 History of the Periodic Table

3 5.1 Objectives Explain the roles of Mendeleev and Moseley in the development of the periodic table. Describe the modern periodic table. Explain how the periodic law can be used to predict the physical and chemical properties of elements. Describe how the elements belonging to a group of the periodic table are interrelated in terms of atomic number.

4 5.1 History of the Periodic Table By 1860, more than 60 elements had been discovered Total confusion amongst scientists though, with different atomic masses and formulas between chemists Sept 1860 International meeting of chemists (Karlsruhe Congress) Cannizzaro Presented method for determining mass that became standard

5 5.1 Dmitri Mendeleev Russian chemist, writing a chemistry book Arranged elements into vertical columns by increasing atomic mass Noticed patterns in their properties along the horizontal rows

6 Dmitri Mendeleev Periodic functions Properties of the elements that repeat in a regular manner 1871 he predicted the existence and properties of the elements that would fill 3 of his spaces By 1886 all 3 had been discovered (scandium, gallium, germanium)

7 5.1 History of the Periodic Table Mendeleev s success persuaded most chemists to accept his periodic table, but two questions remained unsolved: 1. Why could most elements be arranged in order of increasing atomic mass but a few could not? 2. What was the reason for chemical periodicity?

8 5.1 Moseley and Periodic Law Henry Moseley, working with Rutherford, found a previously unrecognized pattern Elements fit better when arranged by nuclear charge, or the number of protons Periodic Law The physical and chemical properties of the elements are periodic functions of their atomic numbers

9 5.1 Modern Periodic Table Periodic table An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column, or group We now know that it is the electron configuration that determines the chemical and physical properties

10 5.1 Electron Configuration 1. Noble gases Completely filled s & p orbitals, nonreactive 2. Main group elements (Groups 1-2, 13-17) s & p blocks 3. Transition metals d block 4. Inner transition metals lanthanide & actinide f block

11 5.2 Periods Elements are arranged vertically by groups with similar chemical properties Also arranged into rows, or periods The length of each period is determined by the number of electrons that can occupy the sublevels being filled in that period

12 Chapter 5.2 Electron Configuration and the Periodic Table

13 5.2 Group Group Presentations As a group, you will choose a group of the periodic table to learn about. You will present information about your chosen group to the class. More information will be provided in class!

14 Chapter 5.3 Periodic Properties

15 5.3 Objectives Define atomic and ionic radii, ionization energy, electron affinity, and electronegativity. Compare the periodic trends of atomic radii, ionization energy, and electronegativity, and state the reasons for these variations. Define valence electrons, and state how many are present in atoms of each main-group element. Compare the atomic radii, ionization energies, and electronegativities of the d-block elements with those of the main-group elements.

16 5.3 Forces Affecting Periodic Trends 1. Nuclear charge Greater number of protons in the nucleus = greater positive charge = stronger the electrons are held 2. Electron Shielding Electrons in the inner energy levels partially shield the outer electrons from the effects of the nuclear charge 3. Electron configuration Atoms are most stable when their outer orbitals are filled (s & p sublevels)

17 5.3 Atomic radius Atomic radius One-half the distance between nuclei of identical atoms that are bonded together Period trend Decreases as move across a period Due to greater nuclear charge pulling in electrons closer Group trend Increases as move down a group Due to increased number of energy levels

18 5.3 Ionic Radii Ions are charged particles Cation = POSITIVE ion (lost an electron) Anion = NEGATIVE ion (gained an electron) Period trend Cations get smaller as move across a period (lose electrons) Anions get larger as move across a period (greater shielding) Group trend Increase as move down a group (more energy levels)

19 5.3 Ionization energy Energy required to ionize an atom Ionization Any process that results in the formation of an ion Period trend Increases as move across a period Due to increasing nuclear charge attracting electrons stronger Group trend Decreases as move down a group Due to electron shielding and outer electrons being further away from nucleus

20 5.3 Electron affinity Measure of the energy given off when an electron is added to a neutral atom to form a negative ion A + e - A - + energy Period trend Increases (becomes more negative) as move across a period Form more stable negative ions because of electron configuration (closer to full) Group trend Decreases (becomes more positive) as move down a group Due to increased atomic radius

21 5.3 Electronegativity The ability of an atom in a molecule to draw bonding electrons to itself, scales from 0-4 Most electronegative element? Period trend Increases as move across a period Due to greater nuclear charge Group trend Decreases as move down a group Due to electron shielding

22 5.3 Valence electrons Number of electrons in outmost energy level Group # valence electrons 1 1 ns ns ns 2 p ns 2 p ns 2 p ns 2 p ns 2 p ns 2 p 6 Electron configuration

23 Origin of the Elements Part I The Universe Big Idea: Students will understand that all matter in the universe has a common origin and is made of atoms, which have structure and can be systematically arranged on the periodic table. Objective 1: Recognize the origin and distribution of elements in the universe.

24 The Universe Includes all energy and matter, including all space and time 14 billion years old Contains hundreds of billions of galaxies, including our galaxy Each galaxy has hundreds of billions of stars ALL ordinary matter in the universe is composed of the same elements!

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26 Size of the Universe

27 Origin of the Universe At the beginning, the entire universe was compressed into a tiny, hot, dense mass 14 billion years ago, an explosive expansion occurred all matter and energy began moving outward in a giant cloud The Big Bang

28 Big Bang Theory As the universe expanded, it became less dense and began to cool Atoms began to form primarily Hydrogen (H) and Helium (He) Matter was held together in clumps due to gravity, which became galaxies

29 Big Bang Evidence What evidence supports the Big Bang theory? Four pillars of the Big Bang theory 1. Redshift 2. Abundance of light elements 3. Cosmic background radiation 4. Observations of galaxy formation and evolution

30 Redshift Elements in stars absorb predictable wavelengths of light, which appear as dark bands when viewed through a prism Light from distant galaxies was shifted towards the red end of the spectrum, which occurs when a light source is moving away from the observer Sun Distant galaxies

31 Redshift cont. Redshift is similar to the Doppler effect Almost every galaxy in the universe has a redshift, therefore they are all moving away from Earth

32 Abundance of light elements Currently, light elements like helium (He) are only made in stars during nuclear fusion, as extremely hot temperatures are required Helium makes up about 24% of the mass in the universe, which is much more than expected if stars were the only source Therefore, the universe must have had an early hot phase

33 Cosmic background radiation Cosmic background radiation light energy leftover from the Big Bang Seen as heat using microwave receivers on radio telescopes Oldest light in the universe

34 Galactic observations Distant galaxies are not only far away in space, but also in time c = 186,000 mi/s Location Sun Proxima Centuri Andromeda Galaxy z8_gnd_5296 galaxy Time for light to reach Earth 8 minutes 4 years 2.5 million years 13 billion years Observations of these distant galaxies provide windows into the past

35 Origin of the Elements Part II Elements in the Universe

36 Stellar Evolution Nuclear fusion powers stars throughout their lives Nuclear fusion = two or more atomic nuclei join together into a single nucleus The elements undergoing fusion evolves as stars age Main sequence stars H fuses into He As the star ages, other elements may begin to form, depending on the mass of the star

37 Heavy Elements Elements up to iron (Fe) may form in a star via nuclear fusion Elements heavier than Fe can only form during a supernova (e.g. gold, silver, and uranium)

38 Supernova Supernova a massive explosion of a dying star that creates and sends heavy elements flying into space youtube.com/ watch?v=9d0 5ej8u-gU

39 Supernova

40 Nebular Theory Nebula big cloud of gas and dust containing: H and He from the Big Bang Heavier elements from supernovas Orion nebula

41 Nebular Theory cont A. Gravity caused part of our solar nebula to contract and start to spin, going faster as it became smaller B. As it spun faster, it collapsed into a disc with most of the mass in the center Temperature and density increased in the center until nuclear fusion began and the sun was born - protosun

42 Nebular Theory cont C. The rest of the disc began cooling, causing elements and compounds to condense into tiny solid particles Heavier elements condense closest to the sun, lighter elements further out D. Collisions between the solid particles form larger bodies E. The larger bodies accrete to form planets

43 Distribution of the Elements Elements are not distributed uniformly throughout the Universe Element Approximate % Abundance H 74% He 24% O 1% C 0.5% Ne 0.1% Fe 0.1% N 0.1%

44 Origin of the Elements