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Bonding

Bonding. Ionic and covalent. Key Terms 1. Chemical formula– the combination of chemical symbols and subscripts to indicate what the elements are in the compound and how many atoms of each element are in the compound Example: H 2 O= two hydrogen atoms and 1 oxygen atom. Key Terms 2.

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Bonding

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  1. Bonding Ionic and covalent

  2. Key Terms1 • Chemical formula– the combination of chemical symbols and subscripts to indicate what the elements are in the compound and how many atoms of each element are in the compound • Example: H2O= two hydrogen atoms and 1 oxygen atom.

  3. Key Terms2 • The octet rule– each atom wants to have 8 electron in its outer most energy level. • Atoms can share, take, or give away electrons to accomplish this. • Valence electrons– electrons in the outer most energy level that are responsible for the reactivity of that atom.

  4. Key Terms3 • Lewis structure (electron-dot notation)– valence electrons are shown as dots around the element’s symbol. Label the # of Ve- on your periodic table. • Because each orbital can hold two electrons, electrons are grouped in pairs forming the shape of a box around the element’s symbol. • Paired electrons can also be represented by a dash instead of dots if they are being shared in a compound.

  5. Key terms4

  6. Ions • Ion– any atom that has given up or taken electrons to create a positive or negative charge. • This is done to fill the highest energy level. • Cations (cat-ion) – any element that has given away its electrons to become a positively charged ion. Cations are metals. • Anions– any element that has taken electrons to become a negatively charged ion. Anions are nonmetals.

  7. Atoms and charges • What happens when an atom gains or looses an electron? • The atom becomes charged! • Example: Copper has an atomic number of 29. This means copper has 29 electrons(-) and 29 protons(+). If copper were to loose two electrons, what would copper’s charge be? 29 Protons (+) + 27 Electrons (-) 2 Protons left over, each proton has a positive charge so the charge of copper would be +2!

  8. Practice Problem • Oxygen has an atomic number of 8 and an atomic mass of 16. How many neutrons does oxygen have? • Answer: 16= N+8, N=8 • What would Oxygen’s charge be if it gained two electrons? • Answer: 8(+ protons) + 10 (- electrons)=-2

  9. Ionic Bonding

  10. Ionic Bonding • Ionic bonding– any bond between metals and nonmetals (cations and anions) • Charges are based on how many Ve- are needed to fill the outer shell or drop to the previous full shell. Label this on your table. • The charges must cancel each other out. • Example: Na (+1) and Cl (-1)=NaCl (0) • Example: Ca (+2) and F (-1)=CaF2 (0) • Ionic compounds are usually solids and in a crystal structure (crystal lattice).

  11. Ionic Compounds • Both ions should have complete outer shells after bonding. • Both elements should have noble gas electron configurations • When naming, the first element always stays the same, but the last element should end with –ide • Ex. MgO= Magnesium Oxide instead of Magnesium Oxygen • Ex. CaCl2= Calcium Chloride vs Chlorine

  12. Covalent Bond Key Terms1 • Molecule: a group of atoms held together by covalent bonds • Covalent bond: when atoms share electrons • Nonpolar covalent bond: electrons are equally shared by all atoms and the electrical charge is balanced • Polar covalent bond: electrons are not shared equally and there is an imbalance in the electrical charge surrounding the molecule.

  13. Polar vs. nonpolar • Polar nonpolar

  14. Key Terms2 • Polar bonds: when atoms in a molecule have an uneven electron distribution. • Bond length: average distance between two bonded atoms • Bond energy: energy required to break a chemical bond and form neutral isolated atoms. • When the bond length gets shorter, the bond energy gets higher

  15. Key Terms3 • Lewis structures must be used to create covalent compounds (molecules). Sorry no short cuts this time. • Single bond: when only two electrons are being shared between two atoms • Double bond: when 4 electrons are being shared between two atoms • Triple bond: when 6 electrons are being shared between two atoms

  16. Covalent Bonds

  17. Covalent Bonding2 • There are no ions involved with covalent bonds which means no charges. • This is a bond between two nonmetals. • Electrons are shared. • The magic number is still 8.

  18. Covalent properties covalent bonds are weaker than ionic bonds they are poor conductors of electricity They have low melting points and boiling points They are usually very dull in appearance

  19. Covalent Nomenclature • When naming covalent compounds, you MUST use prefixes for the first and second words • The only exception is if you only have one atom for the first element. • the less electronegative (furthest to the left on the p/t) element is given first and its full element name is written • -ide is still needed at the end of the second element as well as a prefix

  20. Covalent molecule prefixes • Mono- • Di- • Tri- • Tetra- • Penta- • Hexa- • Hepta- • Octa- • Nona- • Deca-

  21. Covalent nomenclature • Examples • Dihydrogen monoxide (H2O) • Sulfur trioxide (SO3)*there is only one sulfur so no prefix is needed. • Trisilicon tetranitride (Si3N4) • Dinitrogen Pentaoxide (N2O5)

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