Do Now: What are valence electrons? give a definition give an example

Chemical Bonds DO NOW: What makes up an ionic compound? Describe what happens to the electrons in an ionic bond.

Describe what happens to the electrons in an ionic bond. What makes up an ionic compound? A metal and a nonmetal (cation and anion) Describe what happens to the electrons in an ionic bond. The electrons are given away by the cation and taken by the anion There is NO sharing of the electrons

Electronegativity Electronegativity is a measure of an atom’s attraction for another atom’s electrons. Is directly related to Electron Affinity scale that ranges from 0 to 4. Fluorine is the most electronegative

Electron Affinity Electron affinity = “Love” of electrons Energy change accompanying addition of electron to gaseous atom: Cl + e−  Cl−

Electron Affinity & Electronegativity INCREASES INCREASES 1A 8A H 2.1 B 2.0 P As Se 2.4 Ru 2.2 Rh Pd Te Os Ir Pt Au Po At 2.0 - 2.4 ` 1 1 2A 3A 4A 5A 6A 7A Li 1.0 Be 1.5 Al Si 1.8 Ti V 1.6 Cr Mn Fe Co Ni Cu 1.9 Zn 1.7 Ga Ge Nb Mo Tc Ag Cd In Sn Sb Ta W Re Hg Tl Pb Bi 1.5 - 1.9 N 3.0 O 3.5 F 4.0 Cl 3.0 - 4.0 C 2.5 S Br 2.8 I 2.5 - 2.9 2 2 Na 0.9 K 0.8 Rb Cs 0.7 Ba Fr Ra Below 1.0 Mg 1.2 3 3 3B 4B 5B 6B 7B 1B 2B Period Ca 1.0 Sc 1.3 4 4 Sr 1.0 Y 1.2 Zr 1.4 5 5 Linus Pauling (1901 - 1994) awarded Nobel Prize in chemistry in 1954 for his 1939 text, The Nature of the Chemical Bond, and also won the Nobel Peace Prize in 1962 for his fight to control nuclear weapons. The greater the electronegativity of an atom in a molecule, the more strongly it attracts the electrons in a covalent bond. La 1.1  Hf 1.3 6 6 Ac 1.1   7 Electronegativity  1.0 - 1.4 Lanthanides: 1.1 - 1.3 Actinides: 1.3 - 1.5 Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 373

Which element in each pair has a higher electronegativity value? Cl or F C or N Mg or Ne As or Ca

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Bonding Atoms Why do atoms bond? each atom wants a full outermost energy level gain, lose, and share valence electrons to achieve the duet or octet rule gives each atom an electron configuration isoelectronic to that of a noble gas

Chemical Bonds Chemical Bonds attractive force that holds atoms or ions together 3 types: ionic, covalent, metallic - determines the structure of compound - structure affects properties - melting/boiling pts, conductivity etc.

IONIC BOND bond formed between two ions by the transfer of electrons

Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Bond formed by transfer of electrons Examples; NaCl, CaCl2, K2O

Ionic Bonds: One Big Greedy Thief Dog!

IONIC compound Mini-Review: Made of metal cations and nonmetal anions Held together with ionic bonds High MP and BP Crystalline solids at room temperature Brittle Conduct electricity when dissolved in water

COVALENT BOND bond formed by the sharing of electrons

Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Examples; O2, CO2, C2H6, H2O, SiC

A chemical bond in which 2 atoms share electrons. Covalent bonds form between 2 or more nonmetals Both atoms attract the 2 shared electrons at the same time.

Properties of Covalent Compounds Lower melting points and boiling points when compared to ionic compounds Most do NOT dissolve in water DO NOT conduct electricity when dissolved in water (again most do not dissolve). This is because they are not made of ions! Form molecules vs. formula units Solid, liquid, or gas at room temp

Covalent Bonds

Bonds in all the polyatomic ions and diatomics are all covalent bonds

when electrons are shared equally NONPOLAR COVALENT BONDS when electrons are shared equally H2 or Cl2

HONClBrIF Diatomic Molecules Molecules made up of two of the same types of atoms. There are 7 diatomic molecules. H2, N2, O2, F2, Cl2, Br2, I2 HONClBrIF

Hydrogen The hydrogen molecule has a single covalent bond. Shared electron pair H· + ·H  H:H hydrogen hydrogen hydrogen Atom Atom molecule The hydrogen molecule has a single covalent bond. The electronegativity of each hydrogen atom is the same, so the electrons are equally shared.

when electrons are shared but shared unequally POLAR COVALENT BONDS when electrons are shared but shared unequally H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

What types of bonds are present? BaI2 P4S3 Ca(OH)2 FeCO3 B2Cl4 Na2Cr2O7 I2O5 Cu(ClO4)2 CS2