The Periodic Table and Periodic Law

Transcription

1 The Periodic Table and Periodic Law

2 Learning Goals I will be able to recognize that the Periodic Table is organized according to atomic number. I will be able to locate metals, nonmetals, metalloids, including specific groups such as alkali metals, on the period table. I will be able to locate periods and groups and relate them to the energy level and number of valence electrons in an atom.

3 Development of the Modern Periodic Table Newlands: When arranged by atomic mass, properties repeat every eight elements. Meyer & Mendeleev: Also demonstrated a periodic pattern of properties. Mendeleev: Arranged the elements with similar properties into columns (of increasing atomic mass)

4 Mendeleev s Periodic Table Blanks left to indicate elements not yet discovered. Existence of scandium, gallium, and germanium predicted. Properties are as Mendeleev forecast.

5 Modern Statement of Periodic Law Moseley discovered that atoms of each element have a unique number of protons in their nucleus Reorganized the original table by atomic number not atomic mass. Periodic Law: When the elements are arranged by increasing atomic number there is a periodic repetition of chemical and physical properties.

6 Groups columns numbered 1 to 18 Periods rows numbered 1 to 7..

7 Representative elements (tall columns) have a wide range of properties.. They represent every type of element..

8 Transition elements columns 3 thru 12.. all these are metals

9 Inner transition metals lower block Lanthanide series. and Actinide series (radioactive)..

10 Classifying the Elements: Metals Metals: shiny, solids, good conductors of heat and electricity, ductile (forms into wire), malleable (can be shaped) Most elements are metals. Groups 1 thru 12 are metals and some elements in groups 13, 14, and 15

11 Classifying the Elements: Metals Group1: alkali metals Very reactive in water Very soft metals that must be stored in oil or sealed in glass because of their extreme reactivity Group 2: alkali earth metals Also reactive in water; are less reactive than the alkali metals.

12 Classifying the Elements: nonmetals Nonmetals : either brittle, dull solids or gases, poor conductors Group 16 The Oxygen Group Elements form mostly -2 charge anions. Sulfur is also important in the making of sulfuric acid, the most important chemical manufactured in the USA. Group 17 Halogens most reactive nonmetals Group 18 Noble gases un-reactive nonmetals Metalloids (semimetals) along the stairstep line; properties of both metals and nonmetals

13 Learning Check What is the last element in Period 6? Rn Radon What is the second element in Group 17? Cl Chlorine What is the element in Period 4, Group 13? Ga Gallium

14 Learning Check How many Groups are there in the Transition Metals? 10 Name one Inner Transition element.

15 Learning Goal I will be able to relate the position of an element in the periodic table to its electron configuration I will be able to use the periodic table and/ or electron configurations to determine an element's number of valence electrons, and chemical and physical properties.

16 Organizing the Elements by Electron Configuration Electron configurations can be written using a shortcut. Neon 1s 2 2s 2 2p 6 Sodium 1s 2 2s 2 2p 6 3s 1 The first 8 electrons of sodium are in the same orbitals as neon s 8 electrons. Noble gas shortcut [Ne] 3s 1

17 Noble gas shortcut Write the electron configurations for all the Group 1 elements. What do you notice?

18 Elements in a Group have similar electron configurations. lithium Li [He]2s1 sodium Na [Ne]3s1 potassium K [Ar]4s1 rubidium Rb [Kr]5s1 cesium Cs [Xe]6s1 francium Fr [Rn]7s1

19 Learning Check Write the noble gas shortcut electron configuration for Mn Manganese. [Ar]4s 2 3d 5 Write the noble gas shortcut electron configuration for Sn Tin. [Kr]5s 2 4d 10 5p 2

20 Valence Electrons Electrons in the highest principle energy level (only s and p sublevels) Atoms in the same group have the same number of valence electrons. This is why they have the same properties. Valence electrons are related to the elements position on the periodic table. Fr [Rn]7s1 The valence electrons are in the 7 th energy level, 7 th period and s block, 1 st column

21 Learning Check How many valence electrons does bromine have? 7 How many valence electrons does magnesium have? 2

22 Learning Check How many valence electrons does copper have? (Be careful) 2 All transition and inner transition elements have 2 valence electron. Remember, only s and p electrons can be valence electrons.

23 s, p, d, f blocks Four distinct blocks correspond to the four sublevels. Blue s; yellow p; pink d; green - f

24 s, p, d, f, Blocks (cont) s block: s sublevel - 1 orbital, 2 electrons. Therefore, 2 columns p block: p sublevel - 3 orbitals, 6 electrons. Therefore, 6 columns Note: Noble gases have a full s and p sublevel (an octet of electrons) d block: d sublevel - 5 orbitals, 10 electrons. Therefore, 10 columns f block: f sublevel - 7 orbitals, 14 electrons. Therefore, 14 columns

25 Learning Check What is the only block that has metals, nonmetals, and metalloids (semi metals)? P block

26 Learning Goals I will be able to predict trends, such as electronegativity, in atomic properties of elements based on the periodic table. I will be able to relate graphs of periodic trends to atomic structure.

27 Atomic Radii Atomic Radius is defined as how closely an atom lies to a neighboring atom. Down a group, electrons are added to a higher energy level, further from the nucleus so the atom is larger. Across a period, electrons are added to the same energy level, but the growing number of protons pulls in more and more on this energy level, so the atom is smaller.

28 Trends in Atomic Radii (cont)

29 Ionic Radius Ion an atom that has gained or lost one or more electrons. Atoms will generally gain or lose in the most efficient way to achieve an octet (full s and p outer sublevels) of valence electrons.

30 Ionic Radius (cont) Positive ions have lost one or more electrons. Less electrons in the electron cloud means that the protons in the nucleus can attract the remaining electrons even more. Positive ions are smaller than the original atom.

31 Ionic Radii (cont) Negative ions have gained one or more electrons. More electrons means that the protons in the nucleus can exert less attraction toward the electrons. The negative ion is larger than the original atom.

32 Ionization Energy Definition: The energy required to remove an electron from a gaseous atom. Must be enough energy to overcome the attraction between the nucleus and the electron. Related to number of valence electrons. 1 st ionization energy always lower than 2 nd ionization energy.

33 Ionization Energy (cont) Trend within groups: Electrons are added to higher energy levels (further from nucleus); easier to remove as you go down a group lower ionization energies. Trend within a period: Electrons are added to the same energy level and the increase in protons means that the electrons are held more tightly ionization energies increase.

34 Ionization Energy (cont)»

35 Ion Formation Elements with low ionization energies can easily lose electrons will become positive ions (cations). Metals fit in this category. Elements with high ionization energies will not lose electrons. They will either: be unreactive and not form ions noble gases actually attract electrons and become negative ions (anions) most nonmetals.

36 Electronegativity Definition: Ability to attract electrons in a chemical bond. Electrons in higher energy levels shield the nucleus more. These atoms will have less ability to attract electrons in a bond. Down a group electronegativity decreases. Across a period more protons are in the nucleus; electrons are added in the same energy level (no extra shielding) so these atoms have more ability to attract electrons. Across a period, electronegativity increases.

37 Electronegativity (cont) Electronegativity values are arbitrary units: Paulings. Fluorine is highest 3.98 Francium is the lowest 0.7 Noble gases are not assigned values because they do not readily form bonds

38 Learning Check Which atom is larger lithium or potassium? K Which atom is larger bromine or potassium? Br

39 Learning Check Which atom has a higher ionization energy lithium or potassium? K Which atom has a higher ionization energy bromine or potassium? Br