Organizing the Periodic Table

1. Organizing the Periodic Table Chemists use the properties of elements to sort them into groups

2. Mendeleev’s Periodic Table • 1869- Russian chemist & teacher published the first table of elements to be widely accepted • Arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column • Left empty spaces where undiscovered elements would fit

3. The Modern Periodic Table • An arrangement of elements based on a set of properties that repeat from row to row • Elements are arranged according to atomic number • 7 rows or periods- each corresponds to a principle energy level- the # of elements per period varies because the # of available orbitals increases from energy level to energy level • Elements within a column or group have similar properties • Properties w/in a period change as you move across the row, the pattern repeats as you move from one period to the next

4. Periodic Law • When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties Atomic radii decreases Electronegativity decreases

6. Sodium Potassium

7. Metals • 80% of elements • Good conductors of heat and electricity • High luster- reflect light • Solids at room temperature • Ductile

8. Nonmetals • Show greater variation in physical properties • Most are gases at room temp. • Properties opposite metals • Poor conductors • Brittle

9. Metalloids • Show properties similar to metals and nonmetals depending on conditions

11. Use the atomic # to find the # or protons or electrons (in a neutral atom) Round atomic mass to the nearest whole # to get mass # Mass #-Atomic #=neutrons

12. Representative Groups • Valence electron- electron that is in the highest occupied energy level of an atom • Valence electrons play a key role in chemical reactions • Properties vary across a period because the # of valence electrons increases from left to right • Elements in a group have similar properties because they have the same # of valence electrons

13. Valence Electrons • When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. • Electron dot diagram- a model of an atom in which each dot represents a valence electron

14. Ionic Bonds • Elements that do not have complete sets of valence electrons tend to react. • Some elements achieve stable electron configurations through the transfer of electrons between atoms. • When an atom gains or loses an electrons the # of protons does not equal the # of electrons this forms an ion • Ion- charged atom • Formation of an ion requires energy because an electron must be removed Anions are named by using part of the element name and the suffix -ide

15. To become an ion an elements electron must escape the energy levels by gaining a required about of energy called the ionization energy.

16. Formation of Ionic Bond • An ionic bond is an attraction between a cation (metal) and an anion (nonmetal) • A ionic compound is a compound that contains ionic bonds and the net charge must be zero

17. Crystal Lattices Ionic Compounds have high melting points, are poor conductors as solids (good when melted or in solution), and shatter when struck with a hammer.

18. Covalent Bonds Structural Formula Electron dot formula • Nonmetals will sometimes share electrons to achieve a full set of valence electrons • A chemical bond in which two atoms share electrons is a covalent bond • The attraction between the shared electrons and the protons in each nucleus hold the atoms together.

19. Covalent Bonds • Some atoms share more than one pair of electrons to reach a full outer shell of electrons. • Two pairs of electrons- double bond • Three pairs of electrons- triple bond

20. Polar Covalent Bonds • In a covalent compound with more than one type of atom the electrons may not be shared equally • In general, elements on the right of the periodic table and at the top of groups have a greater attraction for electrons (electronegativity) A covalent bond in which the electrons are aren’t shared equally is a polar covalent bond

21. Polar and Nonpolar Molecules Which of these are polar?? • In a polar covalent bond the atom with the greater attraction for electrons has a partial negative charge and the other atom has a partial positive charge. • An atom can have a polar bond and not be a polar molecule. • The type of atoms and its shape determine whether a molecule is polar or not.

22. Attraction Between Molecules • There are forces of attraction between molecules they are not strong as ionic or covalent bonds but they are strong enough to hold molecules together in a solid or a liquid • Attractions between polar molecules are stronger than attractions between non-polar molecules

25. Metallic Bonds • The attraction between the metal cation and the shared electrons around it • In a metal the valence electrons are free to move among the atoms- this accounts for many of the properties of metals

26. Chemical Reactions • In a chemical reaction one or more reactants react to form one or more products • Chemical Equations are used to represent the process of a chemical reaction. • Reactants  Product • Mass is neither created or destroyed during a chemical reaction so the number of atoms on either side of the equation must be equal.

28. Balancing Equations • In order to show that mass is conserved during a chemical reaction the equation must be balanced. • Equations are balanced by changing the coefficient's (the numbers in front of the formulas) • NEVER CHANGE THE SUBSCRIPTS- THAT CHANGES THE IDENTITY OF THE REACTANT OR PRODUCT

29. Types of Reactions • Synthesis- two or more substances react to form a single substance • A + B  AB • Balance this one • Na + Cl2  NaCl

30. Decomposition Reactions • A reaction in which a compound breaks down into two or more simpler substances. • AB  A + B • Balance this one- H2O  H2 + O2

31. Single Replacement Reaction • Reaction in which one element takes the place of another. • A + BC  B + AC • Balance this one- Cu + AgNO3  Ag + Cu (NO3)2

32. Double Replacement Reaction • Two different compounds exchange positive ions and form two new compounds • AB + CD  AD + CB • Try These- PB(NO3)2 + KI  PBI2 + KNO3 CaCO3 + HCL  CaCL2 + H2CO3

33. Combustion A substance reacts rapidly with oxygen often producing heat and light • Balance these CH4 + O  CO2 + H20 H2 + O2  H2O