12.1 Section A and B, 12.2 Group 1 Period 6

Bonds  Bond – a force that holds together two or more atoms and functions as one unit  Bond energy – the strength required to break the bond

Bonds

Example  What’s the difference between bond and bond energy?

Answer  Bonds hold together atoms while bond energy is a characteristic of a bond in which it describes how strong a bond is.

Types of Chemical Bonds  Covalent bond – a bond that forms when two nonmetals react  Ionic bond – a bond that forms when a nonmetal and a metal react  Polar Covalent bond – between two extremes in which atoms are not that different so that there is an unequal sharing of electrons

Methane (covalent bond)

Example  What happens to the electrons in a covalent bond?

Answer  The electrons are shared by each of the atoms.

Electronegativity  Electronegativity – the ability for an atom to attract electrons  Electronegativity increases up a group and across a period  Similar electronegativity results in a covalent bond and different electronegativity results in an ionic bond  Electronegativity ranges from 0-4.0

Electronegativity

Example  On the periodic table, how does electronegativity increase and decrease?

Answer  Electronegativity increases going up a group and across a period(left to right). It decreases going down a group and across a period (right to left).

Electron Configurations  Groups 1 and 2 are the s orbitals – two electrons max in each  Groups 3-12 are the d orbitals – 10 electrons max  Groups are the p orbitals – 6 electrons max  Lanthanides – bottom of the periodic table – have f orbitals and hold 15 electrons  You read across the table to do electron configurations

Electron Configuration

Example  Write the electron configuration for Ca. Tell what noble gas you would use to abbreviate.

Answer  1s^2 2s^2 2p^6 3s^2 3p^6 4s^2  You would use Argon

Structures of Ionic Compounds  When a nonmetal and a metal react they usually form an octet (8 valence electrons)  Stable compounds achieve an octet  Cation is always smaller than the atom and the anion is always bigger than the atom  Cations are the metals and the anions are the nonmetals  Anions are bigger because they are greedy for electrons while the cation are smaller because they have to give up electrons  Polyatomic ions are held together by covalent bonds

Sodium Chloride Crystal Lattice

Example  When a metal and a nonmetal react, in what conditions are they stable?

Answer  When they form an octet they are stable because they have achieved a noble gas electron configuration.

Quiz 1) What are cations? Anions? 2) What happens when a metal loses all of its valence electrons 3) What are the individual polyatomic ions held together by? 4) What is larger the anion or the cation? 5) What is the range of electronegativity?

Answers 1) Cations are the metals and the anions are the nonmetals. 2) It gets smaller because it loses its electrons. 3) Covalent bonds. 4) The anions are always bigger because they gain electrons from the metals. 5) The lowest electronegativity is 0 and the highest is 4.0.

References subtopic 1 subtopic 2 ch4_molecule_big.gif subtopic 3 ens/polar_bond.jpg subtopic 4 ocks_alone.jpg subtopic 5 _chloride_crystal.png