Modern Periodic Table

1. Modern Periodic Table Section 5.1 and 5.2

2. Periodic Law • Dmitri Mendeleev – arranged elements into rows in order of increasing mass • Elements with similar properties are in same column • Also predicted properties for undiscovered elements http://www.chem.msu.su/eng/misc/mendeleev/welcome.html

3. Mendeleev’s Periodic Table

4. Source: http://www.corrosionsource.com/handbook/periodic/

5. Periodic Table • An arrangement of elements in columns, based on a set of properties that repeat from row to row

6. Periods • A row in the table of elements (horizontal) • Period 1 = 2 elements (H and He) • Periods 2 & 3 = 8 elements each • # of elements per period varies b/c the orbitals increase from energy level to energy level for electrons • Orbitals = # beside the period (like 4 above)

7. Example • H (Hydrogen) has 1 electron • He (Helium) has 2 electrons • 1st energy level = 1 orbital • Electrons of H and He fit this orbital • But Li (lithium) has 3 electrons • 2 electrons fit in one orbital, but the third electron must be in the 2nd energy level

8. This is why Li is the 1st element in Period 2 • has 3 electrons, but 2 fit in one orbital, the third must be in the 2nd orbital • What about sodium (Na)? • 1 electron in 3rd energy level • Potassium (K)? • 1 electron in 4th energy level

9. Groups • The columns on the periodic table • Elements within groups have similar properties • Properties of elements repeat in a predictable way when the atomic # are used to arrange elements in groups

10. Groups continued… • They have similar electron configurations (arrangements) • The number at the top = valence electrons (all elements in the group have the same number of valence electrons) • This determines its chemical properties • Periodic law – pattern of repeating properties displayed by elements in periodic table • Look at the chart • How many groups: _____ • How many periods: _____

11. Valence electrons • An electron that is in the highest occupied energy level of an atom • Elements in a group have similar properties because they have the same number of valence electrons

12. Quick Review of Isotopes • Atoms of the same element that have different Neutrons (no charge) and different masses • But they still have the same atomic # • Atomic mass units (amu) – 1/12 the mass of a C-12 atom (6 protons, 6 neutrons) • In nature, most elements exist as a mixture of 2 or more isotopes

13. Example • Chlorine (Cl) • Atomic #17 • Mass of 35.453 amu • So where does this mass come from? • 2 natural isotopes Chlorine-35 & Chlorine-37 • Cl-35 has 17 pro, 18 neutrons • Cl-37 has 17 pro, 20 neutrons (this mass is >)

14. Metals • Some metals are extremely reactive • Compare Au and (Mg) when exposed to air • Au shiny; Mg dulls • Metals in “the middle” are transition metals • Bridge elements from left and right • form compounds with distinctive colors • Good conductors of electricity and heat • Are solid at room temp (except Mercury) • Most are malleable and ductile

15. Nonmetals • Elements that are poor conductors of heat and electric current • Have low boiling points, so many are gases at room temp. • Fluorine (F) #9 is highly reactive • F in toothpaste bonds with Na (sodium)

16. Metalloids • Elements with properties that fall between metals and nonmetals • Ability to conduct electric current varies with temp. • Ex) Silicon (Si) and Germanium (Ge) are good insulators (retain heat) at low temp. but are good conductors (transfer heat) at high temp. • Germanium Silicon 

17. Variation Across A Period • States of matter • Solid: black; liquid: blue; gas: red • General properties • Metals (left) • Nonmetals (right) • Metalloids (in between)