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Chemical Bonding

Chemical Bonding. There are two kinds of pure substances. Elements Compounds. Let’s start the new notes…. Elements. Substance that cannot be separated or broken down into simpler substances by chemical means. Ex’s- any box on the periodic table Made of only 1 type of atom

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Chemical Bonding

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  1. Chemical Bonding

  2. There are two kinds of pure substances Elements Compounds

  3. Let’s start the new notes…

  4. Elements • Substance that cannot be separated or broken down into simpler substances by chemical means. • Ex’s- any box on the periodic table • Made of only 1 type of atom • The smallest unit of an element that maintains the properties of that element • HUH?

  5. The smallest unit of an element that maintains the properties of that element??? • The element sodium has certain properties • 11 protons, 11 electrons, etc and that determines properties like boiling point, etc.

  6. Forming a Compound • Compounds- have properties unlike those of their elements ex. Na-shiny, soft, grey metal Cl- green-yellow gas NaCl- forms table salt Chemical formula- tells what elements it contains & the ratio of the atoms of those elements ex. H2O, Na+1Cl-1 Superscript-indicates charge Subscript-indicates #atoms

  7. Compounds cont… • Substance made of atoms of 2 or more different elements that are CHEMICALLY combined. • Means they are bonded by the valence electrons! • Elements are combined in a definite way and this changes their properties Na- lethal if ingested Cl- lethal if ingested NaCl- table salt

  8. Molecules • Two or more atoms bonded together… • They can be two of the same element or two different elements (compounds) • All compounds are molecules, but not all molecules are compounds. • Ex- O2, NaCl, etc.

  9. Compounds Molecules made by atoms of two or more elements bonded together -always in a definite ratio Elements Made of just one type of atom Ex. Sodium is only made of Na atoms What is a pure substance? NaCl (sodium chloride/salt) Na (sodium)

  10. Chemical Bond • Force which holds atoms together. • 2 major types: •  Ionic • Covalent

  11. Why Bond?? • Chemically stable- if an atom’s outer energy level is completely filled with electrons -most are filled when they contain 8 electrons (OCTET RULE) (exceptions- He, H, Li, Be) ex. Noble gases- inert; chemically stable • So, atoms will try to form compounds by doing chemical reactions and therefore forming bonds. • REMEMBER: ATOMS DON’T LIKE TO BE ALONE!

  12. Why Bond?? • Chemical bond- force that holds together the atoms in a substance *Losing, gaining, and sharing of valence electrons are the means that atoms use to become stable & form chemical bonds. ex. LiF- Li loses 1 electron F gains 1 electron

  13. Ionic Bonds(formed in ionic compounds)Formed between metal & nonmetal atoms (elements). • IONS are the basic unit (atom with a charge). • CATION = ion that has a + charge (lost e-‘s) • ANION = ion that has a – charge (gained e-‘s)

  14. How are these ions made? • Can you mess with protons? • Would messing with neutrons do anything to the charge? • What must you mess with??? • What charge does an electron have? • So what would happen to the atom if they LOSE one? Would they get more positive or more negative overall???

  15. How do ions stick together? • Force of attraction between oppositely charged ions. • (anion & cation) • Ionic bonds are very strong bonds. • Formed between metal & nonmetal atoms (elements). • One atom gives an electron to another atom (remember it’s the losing and gaining of electrons) • Electronegativity difference between the atoms is 1.7 or greater. (see table on last page of notes) • Ex) Na & Cl

  16. Ionic Compounds: • pack into a pattern (crystal; lattice) • have very high melting points.

  17. Ionic Compound Cont… • Dissolve in water (H2O), and ions are then free to move (dissociate). • Conduct electric current.

  18. Let’s Draw Some: • Do you remember how to draw a bohr model? • Draw one for Sodium and one for Chlorine • What do you think will happen?

  19. Bond Diagrams • Ionic Bond- -lose & gain electrons • Ex. NaCl

  20. Ionic Bonds • Sodium atom, Na, that lost an electron is now a sodium ion, Na1+ • Chlorine atom, Cl, that gained an electron is now a chlorine ion, Cl1-

  21. Lets make some Lewis Dot diagrams!!! • Draw a Lewis Dot for Na & Cl. • Draw an arrow to show what the electron will do • Finally draw the ions in the bond.

  22. Let’s put it all together…

  23. Lewis Dot Diagrams

  24. Types of Bonds • Covalent bond – bond that forms b/w atoms when they share electrons -occurs between 2 nonmetals -types- single (shares 1 pair of e) double (shares 2 pairs of e) triple (shares 3 pairs of e) • Usually forms liquids/gases at room temp. *REMEMBER HYDROGEN IS A NONMETAL AND FORMS COVALENT BONDS!!!

  25. Covalent Bonds(formed in molecular/covalent compounds) • Atoms are the basic unit. (atoms bond to form them) • Covalent bonds are firm, but molecules not strongly held together. • Force between atoms that share electrons.

  26. Let’s draw some! • Remember covalent bonds SHARE electrons, so there is no drawing arrows. • Ex- F2

  27. Lewis Dot Diagrams…

  28. Covalent bonds H2-hydrogen gas-sharing of electrons

  29. Steps to help you… • Draw the lewis of each kind of atom in the compound. • Highlight/circle which electrons will be shared • When you draw your molecule- • Draw the center atom in the molecule with all 8 valence electrons (use two “types” like x’s and o’s to show where they came from) • Draw in your other atoms and their valence electrons • Circle each atoms’ “8 electrons”- they will overlap each other where they share 

  30. Ex- Cl2

  31. Kinds of Covalent Bonds • Can share different number of electrons: • Single- share ONE pair of electrons • Double- share TWO pair of electrons • Triple- share THREE pairs of electrons

  32. How do you know which type of bond will form? Use two rules: • Calculation using electronegativity values on a periodic table: •  Subtract the values of the 2 elements (larger minus smaller) • If difference is: 0-0.3 = nonpolar covalent bond >0.3-1.7= polar covalent bond 1.7 & up= ionic bond

  33. Electronegativity Differences summary… If difference is 1.7 & up Electronegativities are so great that one atom will steal the electron away If difference is: >0.3-1.7 Electronegativities are not different enough to steal the electron away, but there will be a “bully” who hugs the electrons closer 0-0.3 difference Electronegativities are the same, so the atoms will share nicely 

  34. A second way… “rule of thumb” • 2) Periodic table/metal, nonmetal rule (Rule of thumb): • Metal and nonmetal = ionic bond • Nonmetal and nonmetal = covalent

  35. Rule of thumb summary… A metal with a nonmetal Two Nonmetals

  36. Covalent/ Molecular Compounds: • Not packed into a pattern. • Have low melting points. • May not dissolve in water (H2O), but some can. • Do not conduct electricity; do not dissociate.

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